(57) Climate Change

 Carbon sequestration focuses on disposing of carbon, not preventing its release

 What Is CO2 Sequestration?


Carbon Sequestration Issues

Carbon sequestration is the collection and storage of carbon dioxide (CO2) to keep it out of the atmosphere. CO2 can be sequestered in the oceans, underground reservoirs, carbon compounds, biomass, or soil. A variety of ways to sequester carbon has been proposed since the 1980s. Some, such as planting trees and changing agricultural practices to sequester carbon in soil, are for the most part uncontroversial but may not be able to sequester enough CO2 to stabilize global climate.

Other methods, such as carbon capture and storage (CCS), have not yet proved to be effective or affordable. Some, such as iron fertilization of phytoplankton (single-celled green plants) in the seas, have not yet proved to be effective and might, according to their scientific critics, do more ecological harm than good even if they are capable of sequestering large quantities of carbon. The leading candidate technology for large-scale carbon sequestration in the near future is CCS.

Historical Background and Scientific Foundations

Human activities have increased the atmospheric concentration of CO2 from 380 parts per million in 1750, before the widespread burning of fossil fuels, to 383 parts per million in 2007, a 37% increase. Other gases have increased as well, but CO2 is the most important greenhouse gas, accounting for 63% of the anthropogenic (human-caused) global warming. The other 37% of warming is due to other greenhouse gases and to changes in albedo (global brightness).

About 84% of CO2 emissions were, as of 2007, from the burning of fossil fuels, with the other 16% coming mostly from deforestation. In the United States in 2006, CO2 emissions were about 86% of greenhouse pollution, and globally about 29.8 billion tons (27 billion metric tons) of CO2 were being emitted yearly. Many climate scientists agree that in order to stabilize global average temperature at no more than about 3.6ºF (2ºC) above its preindustrial value, CO2 emissions must be greatly reduced by mid-century. To limit warming this much, a 2003 study in Science stated that by 2050, 75% to 100% of total power demand would have to be met by non-CO2-releasing sources. Nuclear power, renewable, and energy efficiency have all been proposed as ways to meet energy demand, but many experts believe that energy generation from fossil-fuel point sources such as coal-fired power plants will continue to grow in the coming decades.

As more such plants are constructed, their CO2 emissions are bound to increase unless sequestration is used. Italian energy specialist E. Marchetti suggested geologic or capture-and-store sequestration of CO2 from fossil-fuel burning in 1976. In 1977, he suggested the alternative possibility of pumping CO2 into deep ocean waters, where it would dissolve and remain for centuries until making its way to the atmosphere. However, no action was taken on Marchetti’s ideas, as there did not yet seem any urgent need for sequestration of carbon. Analysis of Marchetti’s ideas in the mid-1980s seemed to show that sequestration would be prohibitively expensive. In the 1990s, public and scientific concern over anthropogenic climate change intensified. In a little over ten years, from about 1995 to 2005, carbon sequestration went from being an idea of interest to only a few specialists to a widely discussed possibility for mitigating climate change, with hundreds of millions of dollars of government funding for demonstration projects from Europe, the United States, and elsewhere. By the late 1990s, the United States was funding studies of CCS in various American geological formations. By 2007, several industrial-scale CCS pilot projects were underway.


Carbon sequestration occurs naturally. Plants extract carbon from the atmosphere to build their tissues, and this carbon may be sequestered as dead plant matter in soils (hundreds of billions of tons are locked up in this form in the permafrost soils of the Arctic region) or even turned, over millions of years, into trillions of tons of oil, coal, and gas deposits. The carbon now being released from fossil fuels was sequestered by green plants hundreds of millions of years ago. The oceans also sequester carbon by absorbing it from the atmosphere: about half of the CO2 emitted by human activities is absorbed in this way, preventing it from enhancing global warming but making the oceans significantly more acidic.

Today’s debates over carbon sequestration focus on allowing natural sequestration to proceed (i.e., by cutting down fewer forests or planting new ones), enhancing natural sequestration processes (i.e., by feeding iron to the phytoplankton floating in ocean surface waters, which transport carbon to the deep ocean when they die and sink), and building CCS systems. Iron fertilization is the most controversial of these options and CCS is the most mature.

Carbon Capture and Storage (CCS)

All CCS technologies have three major parts. First is the capture of CO2, either before or after fuel is burned. Second is the transportation of the captured CO2 to the site where it is to be sequestered. The third is the disposal or sequestration itself. There are three ways of capturing CO2 from fossil fuels, namely pre-combustion, post-combustion, and oxy-fuel combustion. In the first method, pre-combustion capture, chemical reactions are used to extract CO2 from the fuel before it is burned. For example, reacting the fuel with steam (water, H2O) produces two molecules of hydrogen (H2) and one of CO2 for each atom of carbon in the original fuel. The hydrogen may then be burned, producing water as the only byproduct. A steam reaction of this type is already the standard industrial technique for manufacturing hydrogen from natural gas.

The second method of capturing CO2 from fuel, post-combustion capture, first burns the fuel, allowing CO2 to form, then uses chemical reactions to capture the CO2 from the flue gas (hot gas normally sent right up to the chimney or flue). The usual method of post-combustion capture is amine scrubbing. In this technique, the flue gas is bubbled through a watery solution of one or more of the chemicals called amines. This amine solution absorbs the CO2 from flue gas (which consists mostly of nitrogen, because air itself is 78% nitrogen). When heated in another part of the machinery, the amine solution gives up the CO2 in pure form, which is then collected.

A technology for pre-combustion capture that many energy experts view as promising is the integrated gasification combined cycle (IGCC). In IGCC, fuel is mixed with oxygen and steam to produce a burnable gas consisting mostly of hydrogen and carbon monoxide (CO). This first mixture is then reacted with steam to make CO2 and hydrogen. This second mixture can then be burned as-is directly, or the CO2 can be separated, leaving the hydrogen. Typical IGCC heat-to-electric efficiency is about 40% today and could, in theory, be made much higher (around 60%), which would make the energy cost of CO2 capture more affordable. IGCC plants-several of which were already in operation as of 2007, though without carbon capture-cost at least 20% more to build than conventional power plants, but also produce much less air pollution than comparable coal-fired plants.

Oxy-fuel combustion, the third major option for carbon capture in fuel burning, combusts fuel with pure oxygen, which produces flue gas that is mostly CO2 and steam and which can then be separated. Oxy-fuel combustion is already used in a number of power plants

today because it produces more efficient combustion but is not yet used with carbon capture. Carbon capture is the most expensive part of CCS, and depending on the process can consume a good deal of energy. For example, a typical large, centralized, electricity generation plant converts about 30% of the heat released from its fuel into electricity; the other 70% is wasted to the atmosphere. The best conventional plants (e.g., IGCC plants) operate at about 40% conversion efficiency. CCS might decrease the efficiency of an efficient plant from 40% to about 30%.

After capture, transportation is the next major phase of CCS. CO2 is nontoxic, so the main danger with transporting large quantities of it is that it can displace air near accident scenes and so cause suffocation. Also, CO2 that is to be shipped through pipelines must contain almost no water vapor because water and CO2 combine to form carbonic acid (H2CO3), which corrodes ordinary metal parts.

The third phase is sequestration or storage. Once transported by pipeline or tanker ship to an appropriate location, CO2 can be pumped at high pressure into deep boreholes made by standard drilling equipment. There are four basic options for underground (geological) storage. The first is depleted oil and gas reservoirs. Having been emptied of their fossil fuels, these underground pockets can be refilled with CO2. The second option is enhanced gas and oil recovery. In this method, CO2 is injected into gas or oil wells to squeeze out new fuel. These operations typically pay for themselves through the market value of the recovered fuel. The third option is storage in deep saline aquifers (bodies of porous rock permeated with salty water), either onshore or offshore. The fourth is methane (CH4) recovery from coal seams that are too deep to mine. Coal naturally exudes methane, the main ingredient of natural gas. This option, Enhanced Coal Bed Methane Recovery, consists of pumping CO2 into deep coal seams, capturing the methane that is forced out through other boreholes, and burning that methane as a fuel. CCS could be used to capture the CO2 from the burning methane and inject it back into the ground to force out still more methane, and so on. Deep coal deposits in the United States are estimated to have storage potential for about 37 billion tons (33.5 billion metric tons) of CO2, or six years’ worth of emissions. The capacity of deep saline aquifers is uncertain, but the high end of the range of figures quoted by the U.S. Department of Energy is 500 billion tons (454 billion metric tons).

There is little doubt that CCS with geological sequestration can work, at least for the geological short term. Since 1986, Chevron Oil’s Rangely Field project in the United States has used a CO2 injection into underground oil reservoirs to help force petroleum to the surface. As of 2006, the project had sequestered over 26.5 million tons (24 million metric tons) of CO2. In 1991, Norway became the first country to impose a per-ton tax on carbon emissions. In 1996, in order to avoid paying this tax on CO2 pumped from its Sleipner natural gas well in the North Sea, the Norwegian oil company Statoil began disposing of CO2 by injecting it into an aquifer 3,280 ft (1,000 m) below the sea floor. The natural gas obtained from the Sleipner well is unusual in that it consists of 9% CO2, which has to be separated from the gas to make it marketable. The Norwegian tax on CO2 emissions is about US$50 a ton, but it costs Statoil only about US$30 a ton to inject the CO2 into the deep aquifer, making the operation profitable. Statoil sequesters 1 million tons of CO2 per year at Sleipner, enough to increase Norway’s CO2 emissions by 3% if it were all released into the atmosphere. Statoil plans to dispose of, all told about 20 million metric tons of CO2 at the Sleipner well.

In 2007, this was still the largest project for sequestering CO2 that was not part of an enhanced-oil-recovery (EOR) scheme. The Weyburn project in Canada, an EOR project, was also injecting about 1 million tons (907,000 metric tons) of CO2 per year. At the In Salah natural gas well in Algeria, CO2 separated from the gas was being injected back into the ground much as at the Sleipner field. The In Salah plan called for the eventual sequestration of 17 million tons (15.4 million metric tons) of CO2.

The alternative to geological storage is ocean storage. There are two basic options. The first is dissolution type storage, in which a pipeline is run out to sea at a depth of approximately 1 mi (1.5 km). Liquid or gaseous CO2 is then forced through the pipeline, after which it bubbles up through the ocean in a rising plume. The gas dissolves in the ocean before it reaches the surface layer. An alternative form of dissolution-type storage is to run a pipe down to a depth of at least 2 mi (3 km) and dissolve a sinking plume of liquid CO2 in deeper water that will sequester the carbon for a longer period of time.

The second basic type of ocean storage is lake-type storage. In this method, liquid CO2 is deposited on the deep ocean floor at about 2.5 mi (4 km) or greater depth in the form of a cold pool. Some experiments indicate that a skin of stable ice-like hydrates may form over such a pool, slowing its eventual dissolution in the ocean.

Ocean disposal of CO2 was in the research phase in the early 2000s.


Proposed methods of carbon capture other than CCS include the manufacture of carbonate minerals; reformed agricultural practices to encourage carbon uptake by soils; the manufacture of carbon powder and its addition to soils as a fertilizer; planting forests and preventing deforestation; the addition of powdered iron compounds to ocean surface waters to encourage the growth of phytoplankton that will then die and sink, transporting their carbon to deep waters; and more. Most of these methods depend on sequestering carbon after it has been released, rather than capturing it before release as CCS does. As of 2007, pilot projects were underway for all these technology-dependent sequestration schemes.

Impacts and Issues

The goal of carbon sequestration is to reduce the amount of CO2 entering (or staying in) the atmosphere. For any given method or combination of methods, how much carbon is captured depends on several factors, namely the fraction of CO2 captured, the increase in CO2 production needed to achieve a given real output (e.g., amount of electricity) due to lowered efficiency with CCS, leakage of CO2 during transport, and the fraction of CO2 that leaks out of storage over a given time period. Today’s CCS technologies capture about 85–95% of CO2 from gasified fuel or flue gas. Depending on the type of combustion, power plants would need to produce 10–40% more energy to capture this amount of CO2 and compress it into liquid form for disposal, whether underground, at sea, or by some other method. As for retention of CO2 in storage, the disposal of CO2 underground may, in many cases, sequester carbon from the atmosphere for many thousands of years. Disposal in ocean waters would be relatively temporary because CO2 added to the ocean must eventually migrate into the atmosphere until atmospheric and oceanic CO2 are in equilibrium or balance. Scientists believe that CO2 injected in the oceans would equilibrate with atmospheric CO2 in 2,000 years or less.

All methods of sequestering CO2 have expert advocates and expert critics. However, some methods are more widely criticized in the scientific community than others. Iron fertilization of the oceans is probably the most criticized method, followed by oceanic CCS. Critics of iron fertilization charge that although tests have shown that adding finely ground iron particles to surface ocean waters can indeed cause plankton blooms, these tests have not shown that the method significantly increases the transport of carbon to deep waters, where it would be sequestered.

Concerns about CCS, the most mature of the carbon sequestration technologies, include doubts about whether the CO2 will leak out through old boreholes or other geological defects, perhaps cracks caused by earthquakes. The sudden release of a large amount of CO2 could be disastrous for local populations (as well as defeating the greenhouse-abatement goal of putting the CO2 underground originally). A natural demonstration of this possibility occurred in 1986, when a large bubble of CO2 escaped from a volcanic lake in Cameroon, Africa, killing 1,700 people by suffocation. Storing CO2 in aquifers may be unstable because CO2 combines with water to form carbonic acid, which can weaken rock over time. However, no CO2 leakage has yet been observed from any of the pilot CCS sequestration projects now being conducted worldwide.

Ocean storage of CO2 would, according to biologists, injure deep-sea life by making the deep ocean more acidic. Biological communities near injection sites would be devastated at once, while the effect on living things farther away would be more gradual. CO2 from the atmosphere is already making the oceans significantly more acidic. By the end of the twenty-first century, acidification of the oceans may make it difficult for shelly marine creatures such as corals and clams to build their shells at all, even without additional acidity from oceanic CO2 sequestration.

Despite doubts, carbon sequestration may prove to be an indispensable technology in mitigating climate change. As of 2007, the European Union was considering requiring geologic CCS systems for all new coal-burning power plants. In the United States, a government-industry partnership called FutureGen began considering proposals in 2006 for the construction of a $1 billion power plant that would produce hydrogen and 275 megawatts of electricity while using CCS to yield near-zero greenhouse emissions.

The plant was supposed to start construction in 2009 and enter service in 2012 and would act as a demonstration model for the feasibility of CCS on a commercial scale. Other governments worldwide were also participating in various CCS demonstration projects.

Primary Source Connection

The Environmental Protection Agency (EPA) is the lead environmental agency of the United States government. Here, EPA research explores the feasibility and efficiency of various methods of carbon sequestration for reducing greenhouse gas emissions.

Geological Sequestration

Geologic sequestration, a type of carbon dioxide (CO2) capture and storage (CCS) process, is a promising technology for stabilizing atmospheric greenhouse gas concentrations. Instead of releasing CO2 into the atmosphere, geologic sequestration involves separating and capturing CO2 from an industrial or energy-related source, transporting it to a storage location, and injecting it deep underground for long-term isolation from the atmosphere.


The goal of CO2 capture is to produce a concentrated stream of CO2 that can be readily transported to a geologic sequestration site. Capture of CO2 can be applied to large stationary sources such as power plants, cement or ammonia production or natural gas processing. Several technologies, in different stages of development, exist for CO2 capture. Although these technologies are currently used in a limited number of facilities, research is still needed to improve the efficiency and cost.


After the CO2 is captured from the source and compressed, it can be geologically sequestered on-site or transported to a separate injection site. CO2 can be transported as a liquid in ships, road or rail tankers, but pipelines are the most efficient and cost-effective approach for transporting large volumes of CO2. In the U.S., there is a network of CO2 pipelines that supply CO2 to oil and gas fields, where it is used to enhance oil recovery. The majority of the 40 Tg CO2 (Tg = 109 kg =106 metric tons = 1 million metric tons) transported in these pipelines today is produced from natural CO2 reservoirs; however, the same pipelines can carry CO2 captured from industrial facilities. In fact, a synfuels plant located in North Dakota (Dakota Gasification) has been transporting captured CO2 via pipeline to a sequestration site hundreds of miles away in Canada since 2000.

Injection and Sequestration

Once a suitable geologic formation has been identified through detailed site characterization, CO2 is injected into that formation at a high pressure and to depths generally greater than 2625 feet (800 meters). Below this depth, the pressurized CO2 remains ‘‘supercritical’’ and behaves like a liquid. Supercritical CO2 is denser and takes up less space. Once underground, the CO2 occupies pore spaces in the surrounding rock, like water in a sponge. Saline water which already resides in the pore space will compress under pressure and/or move to allow room for the CO2. Over time, the CO2 also dissolves in water and chemical reactions between the dissolved CO2 and rock can create solid carbonate minerals, more permanently trapping the CO2.

Suitable geologic storage sites have a caprock, which is an overlying impermeable layer that prevents CO2 from escaping back towards the surface. Target formations for sequestration include geologic formations, both on and off-shore, that can demonstrate their ability to retain CO2 for very long periods of time. Well-suited formations include the following:

• Deep saline formations, rock units containing water with a high concentration of salts, are thought to have the largest storage capacity.

• Depleted oil and gas reservoirs are also targeted for CO2 sequestration and have a history of retaining fluids and gases underground for geologic timescales. There is also more data available on these formations which may help characterize and better predict the long-term fate of injected CO2.

• Unminable coal beds, which are either too thin or too deep to be mined economically, offer less storage capacity but they have the benefit of enhancing the production of methane, a valuable fuel source. Less is known about the efficacy of using these formations as targets for sequestration, but research is underway to evaluate them.

Storage Capacity

With proper site selection and management, geologic sequestration could play a major role in reducing emissions of CO2 (IPCC, 2005). Current assessments indicate that the storage capacity of these geologic formations is extremely large and widespread, with a significant proportion of storage opportunities in the U.S. In the U.S., an evaluation of CO2 sources and potential storage sites suggests that 95% of the largest 500 point sources (i.e., power plants and other industrial facilities), accounting for 82% of annual CO2 emissions, are within 50 miles of a candidate CO2 reservoir. . . .

Risk Management

There is limited experience with commercial-scale geologic sequestration today. However, closely related and well-established industrial experience and scientific knowledge can serve as the basis for appropriate risk management strategies. Key components of a risk management strategy include appropriate site selection based on thorough geologic characterization, a monitoring program to detect problems during or after injection, appropriate remediation methods if necessary and a regulatory system to protect human health and the environment. . . .

Potential pathways exist for CO2 to migrate from the target geologic formation to shallower zones or back to the atmosphere. These conduits for CO2 leakage could be largely avoided through proper site characterization and selection. Pathways for CO2 leakage include escape through the caprock (if it is compromised by high pressures or chemical degradation), an undetected or reactivated fault or an artificial penetration such as a poorly plugged abandoned well. In addition to careful site selection, a proper monitoring program can help ensure that CO2 does not escape from the storage site. A monitoring system would detect movement of CO2 into shallower formations and allow significant time to take corrective action in order to reduce potential impacts to human health and the environment. Ground water could be affected both by CO2 leaking directly into an aquifer and by saline ground water that enters an aquifer as a result of being displaced by injected CO2. The risk of these impacts can be minimized through appropriate management strategies. Underground injection of CO2 for the purpose of sequestration is regulated by the Underground Injection Control (UIC) Program under the Safe Drinking Water Act (SDWA). The UIC program ensures that injection activities are performed safely and do not endanger current or future sources of drinking water.

Existing and Planned Projects

Internationally, commercial-scale geologic sequestration (greater than 1 Tg CO2 per year) is occurring or planned in various locations. Projects that underway include the Weyburn CO2 Flood Project (Canada), Sleipner (Norway), and In Salah (Algeria).

The Weyburn CO2 Flood Project in Canada is the first international CO2-enhanced oil recovery (EOR) project to be studied extensively. The CO2 source is the Dakota Gasification plant near Great Plains, North Dakota. Unlike traditional EOR operations, the Weyburn operator will not use the conventional end of projects techniques, which can release CO2, but will maintain the site in order to test and monitor long-term sequestration.

Commercial-scale geologic CO2 sequestration is also occurring at the Sleipner West field in the North Sea. Sleipner West is a natural gas/condensate field located about 500 miles off the coast of Norway. The CO2 is compressed and injected via a single well into a 500 foot thick, saline formation located at a depth of about 2,000 feet below the seabed.

In 2004, a CO2 capture and storage project was launched at the In Salah gas field, in the Algerian desert. Approximately 10% of the produced gas is made up of CO2. Rather than venting the CO2, a common practice on projects of this type, this project is compressing and injecting it 5900 feet deep into a lower level of the gas reservoir where the reservoir is filled with water. Around one million tons of CO2 will be injected into the reservoir every year.

Additionally, commercial-scale projects are planned throughout the world. More information can be found on international projects through the Carbon Sequestration Leadership Forum (CSLF), an international climate change initiative focused on the development of improved cost-effective technologies for the separation and capture of CO2 for its transport and long-term safe storage.

In the U.S., the Department of Energy (DOE) is the lead federal agency on research and development of geologic sequestration technologies. The Department of Energy’s Fossil Energy program is developing a portfolio of technologies that can capture and permanently store greenhouse gases. As part of this portfolio, DOE and an industry alliance recently launched FutureGen, an initiative to complete the world’s first near-zero emissions, coal-based power plant with sequestration by 2012.

DOE is also sponsoring a number of small-scale CO2 pilot projects designed to learn more about how CO2 behaves in the sub-surface and answer practical technical questions on how to design and operate geologic sequestration projects.


 <https://www.epa.gov/sites/production/files/signpost/cc.html> (Accessed on June 2, 2017).

 NOVEMBER 29, 2007).



Berstein, Lenny, et al. ‘‘Carbon Dioxide Capture and Storage: A Status Report.’’ Climate Policy 6 (2006): 241–246.

Caldeira, Ken, et al. ‘‘Climate Sensitivity Uncertainty and the Need for Energy Without CO2 Emission.’’ Science 299 (2003): 2052–2054.

Holloway, Sam. ‘‘Storage of Fossil Fuel–Derived Carbon Dioxide Beneath the Surface of the Earth.’’ Annual Review of Energy and the Environment 26 (2001): 145–166.

Jackson, Robert B., et al. ‘‘Trading Water for Carbon with Biological Carbon Sequestration.’’ Science 310 (2005): 1944–1947.

Kintisch, Eli. ‘‘Report Backs More Projects to Sequester CO2 from Coal.’’ Science 315 (2007): 1481.

Lackner, Klaus S. ‘‘Carbonate Chemistry for Sequestering Fossil Carbon.’’ Annual Review of Energy and the Environment 27 (2002): 193–232.

Lackner, Klaus S. ‘‘A Guide to CO2 Sequestration.’’ Science 300 (2003): 1677–1678.

Lal, R. ‘‘Soil Carbon Sequestration Impacts on Global Climate Change and Food Security.’’ Science 3024 (2004): 1623–1627.

Schiermeier, Quirin. ‘‘Putting the Carbon Back: The Hundred Billion Tonne Challenge.’’ Nature 442 (2006): 620–623.

Schlesinger, William H. ‘‘Carbon Sequestration in Soils.’’ Science 284 (1999): 2095.

Web Sites

Sharp, Philip, et al. ‘‘The Future of Coal.’’ Massachusetts Institute of Technology, 2007. <http://web.mit.edu/coal/The_Future_of_Coal.pdf> (accessed June 2, 2017).




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(56) Climate Change

What is a carbon footprint



Carbon Footprint

A carbon footprint is the total amount of greenhouse emissions that result directly and indirectly either from an individual’s lifestyle, a company’s operations, or the full life cycle of a product or service.

Historical Background and Scientific Foundations

Since the late 1990s, the term carbon footprint has become widely used in the public debate on personal and corporate responsibility in response to global climate change. Its ubiquity is largely because it appears to be an easy way of commodifying an individual or company’s CO2 emissions. But despite its frequent popular use, there is no clear scientific definition of the term, and there remains confusion as to what it actually means and measures. Definitions range from direct CO2 emissions to full lifecycle greenhouse-gas emissions. For example, an individual’s carbon footprint for a New York to London return flight would be 1.7 metric tons.

Impacts and Issues

In ‘‘A Definition of a Carbon Footprint,’’ Thomas Wiedmann and Jan Minx showed several discrepancies between different U.K. organizations’ definitions of carbon footprint. For example, ETAP (an environmental body under the jurisdiction of the European Commission), defines it as: ‘‘a measure of the impact human activities have on the environment in terms of the amount of greenhouse gases produced, measured in tonnes [metric tons] of carbon dioxide.’’ The U.K. Parliamentary Office for Science and Technology defines it as: ‘‘the total amount of CO2 and other greenhouse gases, emitted over the full life cycle of a process or product. It is expressed as grams of CO2 equivalent per kilowatt-hour of generation (gCO2eq/kWh), which accounts for the different global warming effects of other greenhouse gases.’’

Wiedmann and Minx suggested the following conglomerate definition, to include activities of people, governments and industries, as well as the impact of goods and services: ‘‘the carbon footprint is a measure of the exclusive total amount of carbon dioxide emissions that is directly and indirectly caused by an activity or is accumulated over the life stages of a product.’’

Despite the differing definitions, a carbon footprint is intended to measure the impact of people and products on the planet. Many important questions remain.

Should a carbon footprint include other greenhouse gases? Should it be defined by an area unit (ha, m2, km2, etc.) as opposed to a mass unit (kg, t, etc.)? Should it include all sources of CO2 emissions (e.g., those that come naturally from the soil) and not just those from fossil fuels? Should it take into account carbon sinks that help Earth reabsorb CO2? Should there be a separate ‘‘ecological footprint’’ that uses a wider range of measures?

Part of the attraction of a carbon footprint is that it gives a clear marker as to an individual or organization’s contribution to and responsibility for greenhouse-gas emissions. Best Foot Forward, a U.K.-based consultancy that specializes in measuring and communicating environmental impact, assesses that the average annual CO2 footprint of a U.S. resident is 25.9 metric tons (28.5 tons). The average annual footprint of a U.K. resident, by comparison, is 11.6 metric tons; and an African, 0.9 metric tons. This is broken down five ways: food 4% (from farming, processing, and shipping); personal travel 34% (road, air, rail, and water); housing 18% (electricity and heating); services 6% (shops, gyms, etc.); and manufacture and construction 38% (factory goods, road building, etc.).

Another reason why the term has entered the ecolexicon so quickly is because it gives conscientious individuals and companies a figure that they can move to neutralize. Once an entity is aware of its carbon footprint, it can take steps to reduce it.

A popular way of neutralizing a carbon footprint is through an offset or carbon-neutral program. One of a host of offsetting companies will use a carbon calculator to estimate the emissions related to whatever activity an individual or company wishes to neutralize. This is then translated into a fee that the offsetting organization will use to offset or ‘‘soak up’’ an equivalent amount from the atmosphere. Different companies operate different schemes to achieve this: some simply plant trees; others invest in green energy sources or cleaner and more energy efficient industrial and household technologies.

Popular offset programs permit individuals and companies to purchase offsets for their homes, cars, offices, and travel.

However, offset schemes are not without criticism. Critics assert that offsetting merely masks the unsustainability of carbon-intensive activities and is often less beneficial or effective than reducing or stopping emissions in the first place. Another criticism of carbon offset programs is their expense-few individuals can afford to offset every-or even a significant portion-of their greenhouse gas emitting activities. Critics further note that some offset schemes may not produce the claimed carbon savings or may do so only after a number of years. For example, tree planting programs can take years to soak up the emissions one has paid to offset. Despite these criticisms, carbon-neutral programs continue to increase in popularity. Participation in carbon-neutral programs has increased since their inception, and some offsets have become less expensive as offset providers have become profitable.

Words to Know

Carbon Calculator: Software device, often accessed through a Web site, that allows an individual or business to calculate their carbon footprint, that is, how much greenhouse warming is generated to support the present mode of existence of that individual or business.

Carbon Offsets: Reductions in emissions of CO2 (or other greenhouse gases) or enhanced removals of such gases from the atmosphere that are arranged by polluters in order to compensate for their releases of greenhouse gases. Carbon offsets may be purchased by individuals or groups.

Carbon Sinks: Carbon reservoirs such as forests or oceans that take in and store more carbon (carbon sequestration) than they release. Carbon sinks can serve to partially offset greenhouse-gas emissions.

Commodify: To make something into a commodity, that is, something which is bought and sold. Some have argued that carbon markets are unethical because they commodify the well-being of Earth itself, on which all life depends.

Eco-Lexicon: The group or class of words (lexicon) devised for, or especially connected with, speech about environmental concerns. Often has a derisive nuance, as in ‘‘Why have ‘Civic’ or ‘Insight’ not entered the eco-lexicon in the way that ‘Prius’ has?’’

Fossil Fuels: Fuels formed by biological processes and transformed into solid or fluid minerals over geological time. Fossil fuels include coal, petroleum, and natural gas. Fossil fuels are nonrenewable on the timescale of human civilization, because their natural replenishment would take many millions of years.

Greenhouse Gases: Gases that cause Earth to retain more thermal energy by absorbing infrared light emitted by Earth’s surface. The most important greenhouse gases are water vapor, carbon dioxide, methane, nitrous oxide, and various artificial chemicals such as chlorofluorocarbons. All but the latter are naturally occurring, but human activity over the last several centuries has significantly increased the amounts of carbon dioxide, methane, and nitrous oxide in Earth’s atmosphere, causing global warming and global climate change.

See also; Economics of Climate Change; Mitigation Strategies; Sustainability.



Kleiner, Karl. ‘‘The Corporate Race to Cut Carbon.’’ Nature Reports: Climate Change 3 (August 2007).

‘‘Please Do Not Sponsor This Tree.’’ New Internationalist 391 (June 2006).

Wiedmann, Thomas, and Jan Minx. ‘‘A Definition of a Carbon Footprint.’’ ISA Research (June 2007).

Web Sites

‘‘Carbon Down, Profits Up.’’ The Climate Group, 2007. <https://www.c2es.org/docUploads/Climate%20Group%203rd%20ed.pdf> (accessed January 13, 2017).

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(55) Climate Change

Carbon Dioxide Equivalent Emissions

Glossary:Carbon dioxide equivalent



Carbon Dioxide Equivalent (CDE)

A carbon dioxide equivalent (CDE, or CO2E) is the standard measure used to report greenhouse gas emissions. It provides a meaningful comparison of greenhouse gas emissions by providing a measure of the quantity of the gas emitted, while taking into account the relative effect of the gas on global warming compared to the effect of carbon dioxide.

Historical Background and Scientific Foundations

Greenhouse gases are gases that contribute to Earth’s greenhouse effect by absorbing and emitting infrared radiation Greenhouse gases directly affect Earth’s atmosphere by absorbing and trapping infrared radiation, thereby contributing to global warming.

Greenhouse gases can also have an indirect effect on the atmosphere. This occurs when a greenhouse gas undergoes a chemical reaction to produce a second greenhouse gas, influences other greenhouse gases (for example, increasing their lifetime), or alters some other aspect of the atmosphere that affects radiation, such as promoting cloud formation. Differences in the effect of each greenhouse gas means that the impact each gas has on the greenhouse effect cannot be measured only by reporting the quantity of each gas released. Instead, greenhouse gas emissions must be reported based on the impact the gas has on the greenhouse effect.

Impacts and Issues

Global warming potential (GWP) is the measure used to indicate the ability of a greenhouse gas to trap heat energy in the atmosphere. The GWP of a greenhouse gas is given as compared to carbon dioxide, which has a GWP of 1. The GWP can also be given over different time horizons. The Intergovernmental Panel on Climate Change (IPCC) has standardized the measurements for 20-year, 100-year, and 500-year GWPs for greenhouse gases.

The 100-year GWPs of methane, nitrous oxide, sulfur hexafluoride, and HFC-23 are 23, 296, 22,000, and 12,000 respectively. This indicates that each gram of methane has the same global warming effect as 23 grams of carbon dioxide, while each gram of HCF-23 emitted has the same global warming effect as 12000 grams of carbon dioxide.

Measures of greenhouse gas emissions are reported by multiplying the GWP of a greenhouse gas by the mass of the emissions of that gas. This measure is known as the carbon dioxide equivalent (CO2E) and allows the amount of each greenhouse gas to be compared based on its effect on global warming.

Words to Know

Greenhouse Gases: Gases that cause Earth to retain more thermal energy by absorbing infrared light emitted by Earth’s surface. The most important greenhouse gases are water vapor, carbon dioxide, methane, nitrous oxide, and various artificial chemicals such as chlorofluorocarbons. All but the latter are naturally occurring, but human activity over the last several centuries has significantly increased the amounts of carbon dioxide, methane, and nitrous oxide in Earth’s atmosphere, causing global warming and global climate change.

Infrared Radiation: Electromagnetic radiation of a wavelength shorter than radio waves but longer than visible light that takes the form of heat.

Intergovernmental Panel on Climate Change (IPCC): Panel of scientists established by the World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP) in 1988 to assess the science, technology, and socioeconomic information needed to understand the risk of human-induced climate change.



Houghton, J. T., et al. Climate Change 2001: The Scientific

Web Sites:

U.S. Department of State, 2014 2014 “Climate Action Report”  <http://www.state.gov/e/oes/climate/ccreport2014/index.htm> (accessed September 7, 2016).



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(54) Climate Change

NASA - A Year in the Life of Earth's CO2 (Video)

The Keeling Curve

The relentless rise of carbon dioxide

carbon dioxide

Carbon Dioxide Concentrations

Carbon dioxide, symbolized by CO2, is a compound in which each carbon atom binds with two oxygen atoms. CO2 is released into Earth’s atmosphere primarily by volcanoes, the burning of fuels containing carbon, and the decay of plant matter. It is removed from the atmosphere mostly by plants, which take carbon from CO2 to build their tissues, and by the oceans, in which CO2 dissolves.

CO2 is found in the atmospheres of Earth, Mars, and Venus. On Earth, it is normally an invisible, odorless gas. Because it is opaque to some infrared radiation (the electromagnetic waves emitted by warm objects), carbon dioxide in the atmosphere slows the loss of heat energy from Earth into space.

CO2 is the most important of the greenhouse gases that are causing Earth to warm, changing climate and weather patterns. Atmospheric CO2 has increased greatly since humans began burning large amounts of coal and petroleum in the nineteenth century. As of mid-2007, CO2 comprised about 383 parts per million (ppm) or 0.0383% of the atmosphere, an increase of more than 36% over its pre-industrial level of about 280 ppm.

Historical Background and Scientific Foundations

One source of information about atmospheric carbon dioxide concentration is direct measurement of the air. Such data have been gathered steadily since 1958, when American geochemist Charles David Keeling (1928-2005) made the first atmospheric CO2 measurements at Mauna Loa Observatory in Hawaii. Keeling found that atmospheric CO2 tracks the growing season in the Northern Hemisphere, which holds most of the world’s vegetation. In the spring and summer, as green plants grow, they remove CO2 from the air; in the winter, fuel burning and plant decay continue to release CO2, while plants absorb little.

The result is a series of peaks and valleys in atmospheric CO2 concentration. From the top of each winter peak to the bottom of each summer valley, CO2 concentration decreases by about 5 ppm. The terminology ‘‘N parts per million’’ means that out of every 1,000,000 gas molecules in a sample of air, N are CO2 molecules. Most of the others are nitrogen (N2) and oxygen (O2). On average, not counting these seasonal variations, the average CO2 concentration is slowly increasing by about 2 ppm per year. A chart of these changes, plotting time horizontally and CO2 concentration vertically, is called a Keeling curve and looks somewhat like an upward-curved saw-blade. In 1958, the CO2 concentration, apart from seasonal ups and downs, was about 315 ppm; today it is over 380 ppm.

In Antarctica and Greenland, annual snowfall has been packing down into thin layers of ice for many years. Small air bubbles trapped in this ice are samples of ancient air. By counting ice layers like tree rings, scientists know how old these samples are. Thus, cylinders of ice (ice cores) drilled out of such deposits reveal the amount of CO2 in the air over long periods of time. The Vostok ice core, drilled in East Antarctica from 1990 to 1994, supplied a continuous series of CO2 samples from 420,000 years ago to the present. In 2004, scientists announced results drilled from an Antarctic location called Dome C that pushed the record back to 740,000 years ago. In 2006, the Dome C ice-core record was increased to 800,000 years-a cylinder of ice some 2 mi (3.2 km) long. These and other data show that human activity over the last 200 years has raised atmospheric CO2 to a level substantially higher than any seen in the last 800,000 years. CO2 is also rapidly increasing at an unprecedented rate. The most rapid rate of increase observed in the last 800,000 years was 30 ppm over 1,000 years, while the most recent increase of 30 ppm has occurred in only the past 17 years.

Impacts and Issues

Most scientists agree that human activity is causing most of the observed increase in atmospheric CO2 concentrations. They also agree that increased CO2 is the primary cause of the recent warming of the world’s climate, which they predict will continue.

International gatherings of scientists such as the Intergovernmental Panel on Climate Change (IPCC) advise that reducing the amount of CO2 that humans add to the atmosphere from this time forward, will result in smaller changes in global climate. There is political disagreement over what steps should be taken to reduce human CO2 emissions. Burning less fossil fuel would reduce emissions, but as modern industrial economies are still deeply dependent on relatively cheap and abundant coal and petroleum, this is a difficult step to take.

Primary Source Connection

The Intergovernmental Panel on Climate Change (IPCC) is not a research organization, but a scientific body established by the World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP). The IPCC was awarded the Nobel

Peace Prize in 2007 for its efforts to educate global policymakers about human-made climate change. The following source from the IPCC’s 2007 report highlights scientific data on the increase over time of atmospheric CO2, CH4, and other greenhouse gases (GHGs).


Current concentrations of atmospheric CO2 and CH4 far exceed pre-industrial values found in polar ice core records of atmospheric composition dating back 650,000 years. Multiple lines of evidence confirm that the post-industrial rise in these gases does not stem from natural mechanisms. The total radiative forcing of the Earth’s climate due to increases in the concentrations of the LLGHGs CO2, CH4 and N2O, and very likely the rate of increase in the total forcing due to these gases over the period since 1750, are unprecedented in more than 10,000 years.

It is very likely that the sustained rate of increase in the combined radiative forcing from these greenhouse gases of about þ1 W m-2 over the past four decades is at least six times faster than at any time during the two millennia before the Industrial Era, the period for which ice core data have the required temporal resolution. The radiative forcing due to these LLGHGs has the highest level of confidence of any forcing agent.

The concentration of atmospheric CO2 has increased from a pre-industrial value of about 280 ppm to 379 ppmin 2005. Atmospheric CO2 concentration increased by only 20 ppm over the 8000 years prior to industrialisation; multi-decadal to centennial-scale variations were less than 10 ppm and likely due mostly to natural processes.

However, since 1750, the CO2 concentration has risen by nearly 100 ppm. The annual CO2 growth rate was larger during the last 10 years (1995–2005 average: 1.9 ppm yr -1) than it has been since continuous direct atmospheric measurements began (1960-2005 average: 1.4 ppm yr  -1).

Increases in atmospheric CO2 since pre-industrial times are responsible for a radiative forcing of +1.66 +/- 0.17 W m[1]2; a contribution which dominates all other radiative forcing agents considered in this report. For the decade from 1995 to 2005, the growth rate of CO2 in the atmosphere led to a 20% increase in its radiative forcing.

Emissions of CO2 from fossil fuel use and from the effects of land use change on plant and soil carbon are the primary sources of increased atmospheric CO2. Since 1750, it is estimated that about 2/3rds of anthropogenic CO2 emissions have come from fossil fuel burning and about 1/3rd from land use change. About 45% of this CO2 has remained in the atmosphere, while about 30% has been taken up by the oceans and the remainder has been taken up by the terrestrial biosphere. About half of a CO2 pulse to the atmosphere is removed over a time scale of 30 years; a further 30% is removed within a few centuries; and the remaining 20% will typically stay in the atmosphere for many thousands of years.

In recent decades, emissions of CO2 have continued to increase. Global annual fossil CO2 emissions increased from an average of 6.4 +/- 0.4 GtC yr -1 in the 1990s to 7.2 +/- 0.3 GtC yr -1 in the period 2000 to 2005. EstimatedCO2 emissions associated with land use change, averaged over the 1990s, were 0.5 to 2.7 GtC yr -1, with a central estimate of 1.6 Gt yr -1.

Since the 1980s, natural processes of CO2 uptake by the terrestrial biosphere and by the oceans have removed about 50% of anthropogenic emissions. These removal processes are influenced by the atmospheric CO2 concentration and by changes in climate.

Uptake by the oceans and the terrestrial biosphere have been similar in magnitude but the terrestrial biosphere uptake is more variable and was higher in the 1990s than in the 1980s by about 1 GtC yr -1. Observations demonstrate that dissolved CO2 concentrations in the surface ocean have been increasing nearly everywhere, roughly following the atmospheric CO2 increase but with large regional and temporal variability.

Carbon uptake and storage in the terrestrial biosphere arise from the net difference between uptake due to vegetation growth, changes in reforestation and sequestration, and emissions due to heterotrophic respiration, harvest, deforestation, fire, damage by pollution and other disturbance factors affecting biomass and soils. Increases and decreases in fire frequency in different regions have affected net carbon uptake, and in boreal regions, emissions due to fires appear to have increased over recent decades. Estimates of net CO2 surface fluxes from inverse studies using networks of atmospheric data demonstrate significant land uptake in the mid-latitudes of the Northern Hemisphere (NH) and near-zero land-atmosphere fluxes in the tropics, implying that tropical deforestation is approximately balanced by regrowth.

Short-term (interannual) variations observed in the atmospheric CO2 growth rate are primarily controlled by changes in the flux of CO2 between the atmosphere and the terrestrial biosphere, with a smaller but significant fraction due to variability in ocean fluxes. Variability in the terrestrial biosphere flux is driven by climatic fluctuations, which affect the uptake of CO2 by plant growth and the return of CO2 to the atmosphere by the decay of organic material through heterotrophic respiration and fires. El Niño-Southern Oscillation (ENSO) events are a major source of interannual variability in atmospheric CO2 growth rate, due to their effects on fluxes through land and sea surface temperatures, precipitation and the incidence of fires.

Words to Know

Fossil Fuels: Fuels formed by biological processes and transformed into solid or fluid minerals over geological time. Fossil fuels include coal, petroleum, and natural gas. Fossil fuels are non-renewable on the timescale of human civilization, because their natural replenishment would take many millions of years.

Greenhouse Gases: Gases that cause Earth to retain more thermal energy by absorbing infrared light emitted by Earth’s surface. The most important greenhouse gases are water vapor, carbon dioxide, methane, nitrous oxide, and various artificial chemicals such as chlorofluorocarbons. All but the latter are naturally occurring, but human activity over the last several centuries has significantly increased the amounts of carbon dioxide, methane, and nitrous oxide in Earth’s atmosphere, causing global warming and global climate change.

Ice Core: A cylindrical section of ice removed from a glacier or an ice sheet in order to study climate patterns of the past. By performing chemical analyses on the air trapped in the ice, scientists can estimate the percentage of carbon dioxide and other trace gases in the atmosphere at that time.

Infrared: Wavelengths slightly longer than visible light, often used in astronomy to study distant objects.

Intergovernmental Panel on Climate Change  (IPCC): Panel of scientists established by the World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP) in 1988 to assess the science, technology, and socioeconomic information needed to understand the risk of human-induced climate change.

Keeling Curve: Plot of data showing the steady rise of atmospheric carbon dioxide from 1958 to the present, overlaid with annual saw tooth variations due to the growth of Northern Hemisphere plants in summer. Carbon dioxide began rising due to human activities in the 1800s, but direct, continuous measurements of atmospheric carbon dioxide were first made by U.S. oceanographer Charles David Keeling (1928-2005) starting in 1958

B ibliography:


Solomon, S., et al, eds. Climate Change 2007: The Physical Science Basis: Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. New York: Cambridge University Press, 2007.


European Project for Ice Coring in Antarctica. ‘‘Eight Glacial Cycles from an Antarctic Ice Core.’’ Nature 429 (June 10, 2004): 623–628.

Maseh, Betsy. ‘‘The Hot Hand of History.’’ Nature 427 (February 12, 2004): 582–583.

Web Sites:

Amos, Jonathan. ‘‘Deep Ice Tells Long Climate Story.’’BBC News, September 4, 2006. <http://news.bbc.co.uk/2/hi/science/nature/5314592.stm> (accessed July 19, 2016).

‘‘Climate Change Affecting Earth’s Outermost Atmosphere.’’ University Corporation for Atmospheric Research, December 11, 2006. <http://www.ucar.edu/news/releases/2006/thermosphere.shtml> (accessed July 19, 2016).

‘‘Trends in Atmospheric Carbon Dioxide-Mauna Loa; Trends in Atmospheric Carbon Dioxide-Global.’’ U.S. National Oceanic and Atmospheric Administration (NOAA). < http://www.esrl.noaa.gov/gmd/ccgg/trends//> (accessed July 19, 2016).

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(53) Climate Change

Biodiversity News

Biodiversity Ecosystems are failing and extinction rates are soaring. Thomas E. Lovejoy and Edward O. Wilson weigh in on why cataloging existing species, discovering new ones, and maintaining a balanced and diverse global ecosystem are critical for ensuring a habitable environment for all.



Biodiversity is the number of distinct varieties or types within a group of living systems: distinct genes in a species, species in an ecosystem, or ecosystems in a biome. The term is often used to mean the total number of species living in a given ecosystem or on Earth as a whole. Climate change affects biodiversity primarily by shifting the boundaries of ecosystems, by altering the timing of seasonal events such as hatching and budding, and altering the temperature and chemical characteristics of lakes, rivers, and oceans. Atmospheric carbon dioxide (CO2), which is a main cause of global warming, also has direct effects on ecosystems, acidifying the oceans and encouraging the growth of some plants more than others. Such stresses inevitably cause extinctions, that is, loss of biodiversity.

Only evolution can create new species, and this occurs only over geologic time (usually millions of years). On human or historical time scales, extinction decreases biodiversity irreversibly. Some extinctions from climate change have already been recorded, although to date most have been caused by other human activities such as pollution, over-hunting, and deforestation. The rate of extinctions caused by climate change is predicted to be greater later in the twenty-first century than today.

Historical Background and Scientific Foundations


The modern systematic classification of species was invented by Swedish naturalist Carl Linnaeus (1707-1788) in the eighteenth century. In following decades, European naturalists scoured Earth looking for and classifying new species of plants and animals, greatly expanding scientific knowledge of just how diverse life on Earth is.

Such knowledge was crucial to the development of evolutionary biology by Charles Darwin (1809-1882) and others in the mid-nineteenth century. Today, biologists estimate that there are more than 280,000 species of plants and over 1,250,000 species of animals (including insects).

Nineteenth- and twentieth-century paleontology has shown that extinction is a normal process: over 99% of all species that have ever lived are now extinct. The typical lifespan of a species is between 1 and 10 million years. Awareness that species biodiversity is a key feature of ecosystems was not common until the 1970s, however, when the term ‘‘biological diversity’’ first came into frequent use. The word ‘‘biodiversity,’’ a shortening of ‘‘biological diversity,’’ first appeared in print in 1988. In the 1990s and beyond, most biologists have agreed that human beings are causing the first mass extinction in 65 million years. This modern pulse of extinctions is sometimes called the Holocene extinction event. (The Holocene is the geological term for the era from 11,500 years ago to the present.)

Humans are causing extinctions through land development, destruction of rainforests, over-hunting and overfishing, pollution, and other activities. Some of the more famous extinctions of recent times include the dodo bird, the passenger pigeon, and (announced in 2007) the baiji, a white river dolphin of China. Hunting has caused about 23% of known animal extinctions since 1600; the introduction of invasive species, 39%; and habitat destruction, 36%. These numbers are approximate because many of the species that are being destroyed are uncatalogued insects and plants living in rainforests. Estimates of how many extinctions have already occurred due to human activities range from several tens of thousands to over a million. Although impacts by large asteroids have caused or at least contributed to some ancient mass extinctions, climate change has been the most common cause of natural mass extinction. Ancient climate changes were brought about by shifts in Earth’s orbit, continental drift, volcanism, and other processes. Today’s episode of climate change is unique in being caused by a single species, humans. Moreover, today’s mass extinction is unique in that human beings, by taking action to mitigate (reduce the severity of) climate change, can influence the overall severity of the event.

Mechanisms by which Climate Change Affects Biodiversity

As warming continues, other forms of human pressure on biodiversity will continue and will be, in most cases, amplified by the effects of climate change. Although effects may vary fromregion to region, the overall effect of globalwarming is to cause the cooler zones of the world—the regions around the poles (especially the North Pole) and on mountains— to shrink. Shrinkage of habitat puts species at risk because smaller habitats support smaller populations, and smaller populations are always at higher risk of extinction.

Climate change also has many other effects on ecosystems. Some are not immediately obvious. For example, Lake Tanganyika in Africa, the world’s second-largest and second-deepest lake, harbors at least 350 species of fish, most unique to its own waters. Lake Tanganyika is not typical of ecosystems most vulnerable to climate change: being near the equator it is likely to see less drastic warming than, say, the Arctic, while its large thermal mass (4,526 cubic mi of water; 18,900 cubic km) will resist temperature shifts and thus might be expected to moderate climate-change impacts on the lake ecosystem.

However, regional climate warming by 1.08ºF (0.6º C), along with lessened wind speeds, has had rapid effects on Tanganyika’s ecosystem. Warming of surface waters more than deep waters has decreased mixing between the two: warm water is less dense than cool water, so the bigger the temperature difference between the layers, the more stably the warm upper water floats on top of the cool deeper water. Since the deeper waters are more nutrient-rich, reduced mixing has meant that fewer planktonic organisms (tiny, floating organisms, both plants and animals) can thrive in the upper water, where energy from the sun is abundant but nutrients are poor. As of 2003, plankton density in Lake Tanganyika had declined to less than one third what it was 25 years before; algae density had declined by 30% from values 80 years before. Since plankton are the basis of the marine food chain, fish stocks declined along with the plankton: fish stocks in the lake were 30% smaller than they were 80 years earlier.

The reduction of water mixing due to climate warming has made other changes in the lake’s chemistry: for one, oxygen dissolved from the air no longer mixes as well in deeper waters. As a result, the habitat has shrunk for some of the lake’s endemic species, such as the snail Tiphobia horei, which in 1890 lived at depths down to 1,000 ft (300 m) but as of 2003 lived only down to 330 ft (100 m). The snail’s habitat has thus shrunk by about two thirds, even though the lake itself has not shrunk and its bulk average temperature has changed only slightly.

Tanganyika surface plankton loss has been reflected in declining food-fish harvests from the lake (about 400,000 tons per year in 2003). Since Tanganyika supplies 25-40% of the protein needs of the four nations bounding the lake, such declines can have direct impacts on human populations as well as on biodiversity. Losses in biodiversity have not yet been measured directly in Tanganyika, but smaller populations will put some species at risk of extinction, especially as warming in the region continues to about 2.7º F (1.5º C), possibly higher, with even more drastic stabilization of the lake’s waters and consequent effects on its ecosystem.

Slight changes in climate can lead to pressures on biodiversity by other mechanisms. For example, a 2006 study by J. Alan Pounds and colleagues found that global warming has almost certainly caused the recent extinction of about 67% of the 110 or so species of the Monteverde harlequin tree frog of the mountains of Costa Rica. The scientists saw the extinctions as validating the climate linked epidemic hypothesis, according to which shifts

in temperature, rainfall, and other climate variables make populations more vulnerable to disease and therefore to extinction. In the case of the Monteverde frogs, more frequent warm years shifted conditions toward the growth optimum of the Bactrachochytrium fungus, which infects the frogs. The researchers found that extinctions of the frogs consistently followed temperature peaks that were favorable to growth of the fungal disease.

Other effects are not strictly changes in climate, in the sense of temperature or precipitation, but chemical changes to air and water. Increased carbon dioxide (CO2) in the atmosphere has two major effects that are likely to decrease biodiversity:

1) Heightened atmospheric CO2 causes increased levels of dissolvedCO2 in the ocean. When CO2 dissolves in water, it produces a weak acid, carbonic acid. Rising atmospheric CO2 thus acidifies the oceans.

 2) Green plants extract carbon from the air by breaking up CO2, constructing their tissues using the carbon, and releasing the oxygen. CO2 is plant food. Thus, increasing atmospheric CO2 tends to cause more rapid growth in most plant species, an effect called CO2 enrichment.

Acidification of the oceans by dissolved excess CO2 will impact biodiversity by making survival more difficult for organisms that form shells of calcium carbonate. This includes bivalves such as clams, mollusks such as periwinkles and conches, microscopic plankton species, and corals. Corals, which are also subject to bleaching in excessively warm waters, form large, shallow communities in tropical waters that have been compared to rainforests because of their high level of biodiversity. A typical large reef may support on the order of a million species of plants and animals.

Over the last two centuries, the average pH of the oceans has fallen by 0.1, corresponding to a rise in acidity and a 30% reduction in the number of carbonate ions (CO3 2–) available to shell-making organisms as building material. When carbonate ions fall below a certain level, corals have difficulty making their skeletons. This threshold may be reached if the atmospheric CO2 level, today about 375 parts per million, rises to over 500 parts per million, as may occur by the end of the twenty-first century.

Increasing atmospheric CO2 will also affect plant growth. Farmers today often add CO2 to the air inside greenhouses, because under indoor conditions, extra CO2 speeds plant growth and increases crop yields. Under outdoor conditions, however, the gain in yield is about half as much and the foods produced are significantly lower in protein and minerals. In the wild, rising CO2 will favor some species over others, depending on rooting depth, woodiness, and photosynthetic chemistry; this will impact biodiversity by altering competitive balances. The CO2 fertilization effect will be strongest in biomes where plant growth is limited by water availability, such as grasslands, savanna, and desert. The biodiversity impact of a 2.5-fold increase in CO2 would likely be only about a third as great on a boreal (northern pine) forest as on savanna or grassland, and half as great as on desert.

Impacts and Issues

Global Patterns

Most plants require a specific range of temperature, moisture, and seasonal change to thrive; most animals require certain plants or other animals to thrive, and also have a limited range of tolerance for temperature and moisture. As climate warms, a typical ecosystem will tend to migrate away from areas where it was at the warm edge of its tolerance range and toward places where it was formerly at the cool edge. The most general effect of global climate change is thus to move ecological zones toward the poles and toward higher altitudes. For each 1.8ºF (1º C) of warming, terrestrial (on-land) ecosystems typically shift pole ward by 100 mi (160 km): for example, if climate warms by 5.4ºF (3º C) by 2100, plant and animal communities in the Northern Hemisphere will migrate an average of 300 mi (480 km) northward-if they can-to stay in a suitable climate zone. This effect is observed, not only predicted.

In the Northern Hemisphere, terrestrial animal and plant ranges have been observed to shift northward, on average, by 3.8 mi (6.1 km) per decade over the last 50 years. In mountainous terrain, plant and animal ranges have shifted upward by 20 ft (6.1 m) over the same time period. Fragmentation of landscapes by human activity such as agriculture and city-building makes ecosystem migration more difficult today than during past climatic shifts, such as glacial periods. Species that fail to colonize new areas as the climate changes may go extinct.

Although climate change has so far been most intense in the Arctic and the West Antarctic Peninsula, where warming has been about twice the global average and dramatic effects such as retreating sea ice and melting tundra are readily visible, biodiversity is low in these regions compared to the tropics, where rainforests, coral reefs, and other particularly diverse communities are found. Thus, a smaller climate shift can have a greater impact on biodiversity in the tropics than a larger shift in boreal or temperate regions. For marine ecosystems, changes in circulation patterns, ocean temperature, and ocean chemistry all influence biodiversity. For example, over the last 40 years or so, warm-water plankton species have shifted about 620 mi (1,000 km) in the North Atlantic due to warming.

Not all observed climate effects on biological systems are consistent with climate warming; a few are consistent with cooling. Also, some observed effects are consistent with natural climate shifts rather than those attributed to human-caused (anthropogenic) global warming. However, mathematical analysis shows that the very great majority of changes are consistent with warming trends, and that a combination of natural and anthropogenic climate changes describe observed changes in physical and biological systems better than either natural or anthropogenic changes alone. Anthropogenic changes have been added to or laid over those caused by natural processes, and are gradually becoming more dominant.

Future Impacts

The five main drivers of biodiversity change, ranked from most severe impact to least severe between now and 2100, are:

1) land-use changes (including deforestation);

2) climate change;

3) nitrogen deposition (from fertilizer use);

4) biotic exchange (the introduction of invasive species); and

5) direct effects of increasing atmospheric CO2, apart from climate change.

The result of these combined, continuing, and growing pressures will be an irreversible loss of biodiversity in many parts of the world. However, many uncertainties remain. Ecologists do not understand the relationship between ecosystem structure and rapid climate change well enough to predict the exact effects of current climate changes on biomes. It is also unknown whether efforts to mitigate climate change will occur or succeed, and if so, to what extent.

Despite these uncertainties, scientists have estimated the likely impact that climate change will have on biodiversity. In 2004, Chris Thomas and colleagues published their study of an unbiased or representative sample of 1,103 animal and plant species. They found that climate change was likely to commit 15-37% of all species examined to extinction by 2050. ‘‘Committed to extinction’’ does not mean that a species would necessarily be extinct by that time, but that the population of each species would be so reduced that its species’ extinction becomes highly likely.

In many or most ecological regions, climate change will become the greatest threat to biodiversity by 2050. There are 5 to 15 million species of creatures on Earth (the large range arises from the difficulty of counting insect, bacterial, and fungal species). If only 15% of all species are committed to extinction by climate change-the lower end of the range given by Thomas and colleagues-then 750,000 to 2,250,000 million species will eventually become extinct as a result of global climate change.

Primary Source Connection

Human activities and the resulting global climate change have had, and will continue to have, a major impact on biodiversity across the globe. Biodiversity is the variety of all living organisms that exist in an ecosystem. This paper from the Intergovernmental Panel on Climate Change (IPCC) discusses the effect of human activity on biodiversity and possible adaptation and mitigation strategies. The IPCC is a scientific panel that was founded by the United Nations in 1988 as part of the United Nations Environment Program and the U.N.’s World Meteorological Organization.

Climate Change and Biodiversity

At the global level, human activities have caused and will continue to cause a loss in biodiversity through, inter alia, land-use and land-cover change; soil and water pollution and degradation (including desertification), and air pollution; diversion of water to intensively managed ecosystems and urban systems; habitat fragmentation; selective exploitation of species; the introduction of non-native species; and stratospheric ozone depletion.The current rate of biodiversity loss is greater than the natural background rate of extinction. A critical question for this Technical Paper is how much might climate change (natural or human-induced) enhance or inhibit these losses in biodiversity?

Changes in climate exert additional pressure and have already begun to affect biodiversity. The atmospheric concentrations of greenhouse gases have increased since the pre-industrial era due to human activities, primarily the combustion of fossil fuels and land-use and land-cover change. These and natural forces have contributed to changes in the Earth’s climate over the 20th century: Land and ocean surface temperatures have warmed, the spatial and temporal patterns of precipitation have changed, sea level has risen, and the frequency and intensity of El Niño events have increased. These changes, particularly the warmer regional temperatures, have affected the timing of reproduction in animals and plants and/or migration of animals, the length of the growing season, species distributions and population sizes, and the frequency of pest and disease outbreaks. Some coastal, high-latitude, and high-altitude ecosystems have also been affected by changes in regional climatic factors.

Climate change is projected to affect all aspects of biodiversity; however, the projected changes have to take into account the impacts from other past, present, and future human activities, including increasing atmospheric concentrations of carbon dioxide (CO2). For the wide range of Intergovernmental Panel on Climate Change (IPCC) emissions scenarios, the Earth’s mean surface temperature is projected to warm 1.4 to 5.8º C by the end of the 21st century, with land areas warming more than the oceans, and the high latitudes warming more than the tropics. The associated sea-level rise is projected to be 0.09 to 0.88 m. In general, precipitation is projected to increase in high-latitude and equatorial areas and decrease in the subtropics, with an increase in heavy precipitation events. Climate change is projected to affect individual organisms, populations, species distributions, and ecosystem composition and function both directly (e.g., through increases in temperature and changes in precipitation and in the case of marine and coastal ecosystems also changes in sea level and storm surges) and indirectly (e.g., through climate changing the intensity and frequency of disturbances such as wildfires). Processes such as habitat loss, modification and fragmentation, and the introduction and spread of nonnative species will affect the impacts of climate change.

A realistic projection of the future state of the Earth’s ecosystems would need to take into account human land- and water-use patterns, which will greatly affect the ability of organisms to respond to climate change via migration.

The general effect of projected human-induced climate change is that the habitats of many species will move pole ward or upward from their current locations. Species will be affected differently by climate change: They will migrate at different rates through fragmented landscapes, and ecosystems dominated by long-lived species (e.g., long-lived trees) will often be slow to show evidence of change. Thus, the composition of most current ecosystems is likely to change, as species that make up an ecosystem are unlikely to shift together. The most rapid changes are expected where they are accelerated by changes in natural and anthropogenic non-climatic disturbance patterns.

Changes in the frequency, intensity, extent, and locations of disturbances will affect whether, how, and at which rate the existing ecosystems will be replaced by new plant and animal assemblages. Disturbances can increase the rate of species loss and create opportunities for the establishment of new species. Globally by the year 2080, about 20% of coastal wetlands could be lost due to sea-level rise. The impact of sea level rise on coastal ecosystems (e.g., mangrove/coastal wetlands, sea grasses) will vary regionally and will depend on erosion processes from the sea and depositional processes from land. Some mangroves in low-island coastal regions where sedimentation loads are high and erosion processes are low may not be particularly vulnerable to sea-level rise.

The risk of extinction will increase for many species that are already vulnerable. Species with limited climatic ranges and/or restricted habitat requirements and/or small populations are typically the most vulnerable to extinction, such as endemic mountain species and biota restricted to islands (e.g., birds), peninsulas (e.g., Cape Floral Kingdom), or coastal areas (e.g., mangroves, coastal wetlands, and coral reefs). In contrast, species with extensive, non-patchy ranges, long-range dispersal mechanisms, and large populations are at less risk of extinction. While there is little evidence to suggest that climate change will slow species losses, there is evidence it may increase species losses. In some regions there may be an increase in local biodiversity-usually as a result of species introductions, the long-term consequences of which are hard to foresee.

Where significant ecosystem disruption occurs (e.g., loss of dominant species or a high proportion of species, or much of the species redundancy), there may be losses in net ecosystem productivity (NEP) at least during the transition period. However, in many cases, loss of biodiversity from diverse and extensive ecosystems due to climate

change does not necessarily imply loss of productivity as there is a degree of redundancy in most ecosystems; the contribution to production by a species that is lost from an ecosystem may be replaced by another species. Globally, the impacts of climate change on biodiversity and the subsequent effects on productivity have not been estimated.

Changes in biodiversity at ecosystem and landscape scale, in response to climate change and other pressures (e.g., changes in forest fires and deforestation), would further affect global and regional climate through changes in the uptake and release of greenhouse gases and changes in albedo and evapotranspiration. Similarly, structural changes in biological communities in the upper ocean could alter the uptake of CO2 by the ocean or the release of precursors for cloud condensation nuclei causing either positive or negative feedbacks on climate change.

Modeling the changes in biodiversity in response to climate change presents some significant challenges. The data and models needed to project the extent and nature of future ecosystem changes and changes in the geographical distribution of species are incomplete, meaning that these effects can only be partially quantified.

Impacts of climate change mitigation activities on biodiversity depend on the context, design, and implementation of these activities. Land-use, land-use change, and forestry activities (a forestation, reforestation, avoided deforestation, and improved forest, cropland, and grazing land management practices) and implementation of renewable energy sources (hydro-, wind-, and solar power and biofuels) may affect biodiversity depending upon site selection and management practices. For example, 1) a forestation and reforestation projects can have positive, neutral, or negative impacts depending on the level of biodiversity of the non-forest ecosystem being replaced, the scale one considers, and other design and implementation issues; 2) avoiding and reducing forest degradation in threatened/vulnerable forests that contain assemblages of species that are unusually diverse, globally rare, or unique to that region can provide substantial biodiversity benefits along with the avoidance of carbon emissions; 3) large-scale bioenergy plantations that generate high yields would have adverse impacts on biodiversity where they replace systems with higher biological diversity, whereas small-scale plantations on degraded land or abandoned agricultural sites would have environmental benefits; and 4) increased efficiency in the generation and/or use of fossil-fuel-based energy can reduce fossil-fuel use and thereby reduce the impacts on biodiversity resulting from resource extraction, transportation (e.g., through shipping and pipelines), and combustion of fossil fuels.

Climate change adaptation activities can promote conservation and sustainable use of biodiversity and reduce the impact of changes in climate and climatic extremes on biodiversity. These include the establishment of a mosaic of interconnected terrestrial, freshwater, and marine multiple use reserves designed to take into account projected changes in climate, and integrated land and water management activities that reduce non-climate pressures on biodiversity and hence make the systems less vulnerable to changes in climate. Some of these adaptation activities can also make people less vulnerable to climatic extremes.

The effectiveness of adaptation and mitigation activities can be enhanced when they are integrated with broader strategies designed to make development paths more sustainable. There are potential environmental and social synergies and tradeoffs between climate adaptation and mitigation activities (projects and policies), and the objectives of multilateral environmental agreements (e.g., the conservation and sustainable use objective of the Convention on Biological Diversity) as well as other aspects of sustainable development. These synergies and tradeoffs can be evaluated for the full range of potential activities-inter alia, energy and land-use, land-use change, and forestry projects and policies through the application of project, sectoral, and regional level environmental and social impact assessments-and can be compared against a set of criteria and indicators using a range of decision making frameworks. For this, current assessment methodologies, criteria, and indicators for evaluating the impact of mitigation and adaptation activities on biodiversity and other aspects of sustainable development will have to be adapted and further developed.


Words to Know

Biome: Well-defined terrestrial environment (e.g., desert, tundra, or tropical forest). The complex of living organisms found in an ecological region.

Coral Bleaching: Decoloration or whitening of coral from the loss, temporary or permanent, of symbiotic algae (zooxanthellae) living in the coral. The algae give corals their living color and, through photosynthesis, supply most of their food needs. High sea surface temperatures can cause coral bleaching.

Geologic Time: The period of time extending from the formation of Earth to the present.

Holocene Extinction Event: The Holocene is the geological period from 10,000 years ago to the present; the Holocene extinction is the worldwide mass extinction of animal and plant species being caused by human activity. Global warming may accelerate the ongoing Holocene extinction event, possibly driving a fourth of all terrestrial plant and animal species to extinction.

Paleontology: The study of life in past geologic time.

PH: Measures the acidity of a solution. It is the negative log of the concentration of the hydrogen ions in a substance.

Plankton: Floating animal and plant life.

In Context: Preserving Biodiversity

‘‘Reducing both loss of natural habitat and deforestation can have significant biodiversity, soil and water conservation benefits, and can be implemented in a socially and economically sustainable manner. Forestation and bioenergy plantations can lead to restoration of degraded land, manage water runoff, retain soil carbon and benefit rural economies, but could compete with land for food production and may be negative for biodiversity, if not properly designed.’’

Source: Metz, B., et al, eds. Climate Change 2007: Mitigation of Climate Change: Contribution of Working Group III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. New York: Cambridge University Press, 2007.


Parry, M. L., et al, eds. Climate Change 2007: Impacts, Adaptation and Vulnerability: Contribution of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. New York: Cambridge University Press, 2007.


Arau´ o, Miguel B., and Carsten Rahbek. ‘‘How Does Climate Change Affect Biodiversity?’’ Science 313 (2006): 1,396–1,397.

Higgins, Paul A. T. ‘‘Biodiversity Loss Under Existing Land Use and Climate Change: An Illustration Using Northern South America.’’ Global Ecology and Biogeography 16 (2007): 197–204.

Jenkins, Martin. ‘‘Prospects for Biodiversity.’’ Science 302 (2003): 1,175–1,177.

Livingstone, Daniel A. ‘‘Global Climate Change Strikes a Tropical Lake.’’ Science 301 (2003): 468–469.

Pounds, J. Alan, et al. ‘‘Widespread Amphibian Extinctions from Epidemic Disease Driven by Global Warming.’’ Nature 439 (2006): 161–167.

Sala, Enric, and Nancy Knowlton. ‘‘Global Marine Biodiversity Trends.’’ Annual Review of Energy and the Environment 231 (2006): 93–122.

Sala, Osvaldo E., et al. ‘‘Global Biodiversity Scenarios for the Year 2100.’’ Science 287 (2000): 1,770–1,774.

Thomas, Chris D. ‘‘Extinction Risk from Climate Change.’’ Nature 427 (2004): 145–148.

Thuiller, Wilfried. ‘‘Climate Change and the Ecologist.’’ Nature 448 (2007): 550–552.

Willis, K. J., and H. J. B. Birks. ‘‘What Is Natural?

The Need for a Long-Term Perspective in Biodiversity Conservation.’’ Science 314 (2006): 1,261–1,265.

Zimmer, Carl. ‘‘Predicting Oblivions: Are Existing Models Up to the Task.’’ Science 317 (2007): 892–893.

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(52) Climate Change



Carbon Dioxide Emissions - Overview of Greenhouse Gases

Gas Encyclopedia


Carbon Dioxide (CO2)

Carbon dioxide consists of one carbon (C) atom doubly bonded to two oxygen (O) atoms to produce the molecular compound O¼C¼O, with the chemical symbol CO2. It does not have color or odor, but carbon dioxide does have a slight sour taste. This acidic flavor is found in carbonated beverages because carbon dioxide gives such liquids their fizz. Under normal temperatures and pressures found on Earth, carbon dioxide is a gas but can also be found in liquid and solid states.

Scientists have learned that carbon dioxide is found in Earth’s atmosphere in a proportion of about 300 to 400 parts per million (ppm). However, as the global climate has been studied, an increase in the concentration of carbon dioxide has been noticed by scientists at a rate of about 0.4% annually. This increase in concentration is important to the study of climate change because scientists contend that a portion of this increase is due to the combustion of fossil fuels and vegetation such as wood, petroleum, and coal.

Historical Background and Scientific Foundations

Flemish chemist Johannes van Helmont (1580-1644) observed that the final mass was less than the initial mass when charcoal burned in a closed container. Van Helmont conjectured the difference was the removal of an invisible substance (eventually identified as carbon dioxide). Later, Scottish chemist Joseph Black (1728-1799) produced an unknown substance-called ‘‘fixed air’’- when he broke down chalk and limestone. Black is generally considered the first scientist to discover carbon dioxide. In addition, Swedish chemist Svante Arrhenius (1859-1927) was the first scientist to publish a paper about carbon dioxide emissions from the burning of fossil fuels. Arrhenius published ‘‘On the influence of carbonic acid in the air upon the temperature of the ground’’ in 1896.

Impacts and Issues

Carbon dioxide plays an important role in the carbon cycle, which involves an exchange of carbon dioxide between the biosphere (living beings), geosphere (land masses), hydrosphere (water bodies), and atmosphere (air). Under photosynthesis, green plants convert carbon dioxide and water into food such as oxygen and glucose. Conversely, plants and animals release carbon dioxide in a process called respiration.

However, humans affect the amount of carbon dioxide released into the atmosphere with their artificially produced activities such as the burning of fossil fuels, clearing of forests, and the use of fuel-powered vehicles. Because of such activity, the concentration of carbon dioxide in the atmosphere has been steadily increasing since about 1850, the start of the second Industrial Revolution. As reported by the United Nations’ Intergovernmental Panel on Climate Change (IPCC), between 1970 and 2004 the increase in CO2 emissions has grown by about 80%. The environmental problem called global warming is a worry to humans because of the noticed increase of greenhouse gases such as carbon dioxide. Scientists are investigating this greenhouse effect to see if the melting of glaciers and icebergs, increased storm activity, and warmer-than-normal temperatures are due to an exaggerated greenhouse effect. By 2050, the IPCC predicts that carbon dioxide in the atmosphere could reach 450 to 550 ppm.

Words to Know

Biosphere: The sum total of all life-forms on Earth and the interaction among those life-forms.

Carbon Cycle: All parts (reservoirs) and fluxes of carbon. The cycle is usually thought of as four main reservoirs of carbon interconnected by pathways of exchange. The reservoirs are the atmosphere, terrestrial biosphere (usually includes freshwater systems), oceans, and sediments (includes fossil fuels). The annual movements of carbon, the carbon exchanges between reservoirs, occur because of various chemical, physical, geological, and biological processes. The ocean contains the largest pool of carbon near the surface of Earth, but most of that pool is not involved with rapid exchange with the atmosphere.

Fossil Fuels: Fuels formed by biological processes and transformed into solid or fluid minerals over geological time. Fossil fuels include coal, petroleum, and natural gas. Fossil fuels are non-renewable on the timescale of human civilization, because their natural replenishment would take many millions of years.

Greenhouse Gas: A gaseous component of the atmosphere contributing to the greenhouse effect. Greenhouse gases are transparent to certain wavelengths of the sun’s radiant energy, allowing them to penetrate deep into the atmosphere or all the way into Earth’s surface. Greenhouse gases and clouds prevent some infrared radiation from escaping, trapping the heat near Earth’s surface where it warms the lower atmosphere. Alteration of this natural barrier of atmospheric gases can raise or lower the mean global temperature of Earth.

Industrial Revolution: The period, beginning about the middle of the eighteenth century, during which humans began to use steam engines as a major source of power.

Photosynthesis: The process by which green plants use light to synthesize organic compounds from carbon dioxide and water. In the process, oxygen and water are released. Increased levels of carbon dioxide can increase net photosynthesis in some plants. Plants create a very important reservoir for carbon dioxide.

Respiration: The process by which animals use up stored foods (by combustion with oxygen) to produce energy




‘‘CCS [CO2 Capture and Storage] in underground geological formations is a new technology with the potential to make an important contribution to mitigation by 2030. Technical, economic and regulatory developments will affect the actual contribution.’’

SOURCE: Metz, B., et al. ‘‘IPCC, 2007: Summary for Policymakers.’’ In: Climate Change 2007: Mitigation of Climate Change. Contribution of Working Group III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change New York: Cambridge University Press. 2007.



Gunter, Valerie Jan. Volatile Places: A Sociology of Communities and Environmental Controversies.

Thousand Oaks, CA: Pine Forge Press, 2007.

Mackenzie, Fred T. Carbon in the Geobiosphere: Earth’s Outer Shell. Dordrecht, Netherlands: Springer, 2006.

National Academy of Engineering, National Research Council of the National Academies. The Carbon Dioxide Dilemma: Promising Technologies and Policies. Washington, DC: National Academies Press, 2003.

Web Sites:

‘‘Contributions of Working Group III to the Fourth Assessment Report of the Intergovermental Panel on Climate Change.’’ Intergovermental Panel on Climate Change, May 4, 2007.  <https://www.ipcc.ch/pdf/assessment-report/ar4/wg3/ar4_wg3_full_report.pdf> (accessed May 3, 2016).

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(51) Climate Change

The Carbon Cycle (Video)


The Carbon Cycle

Carbon Cycle


Carbon Cycle

The carbon cycle describes the reservoirs and transformations that the atom carbon undergoes as it cycles through the atmosphere, lithosphere, biosphere, and hydrosphere (Earth’s air, land, water, and other areas that support life). The carbon cycle plays a key role in climate change because carbon dioxide is perhaps the most important gas contributing to global warming in the atmosphere. In addition, carbon is one of the most basic molecules used by organisms to store energy in chemical bonds.

Historical Background and Scientific Foundations

One of the largest reservoirs of carbon is carbon dioxide in the atmosphere. Plants on land and algae in water-based ecosystems incorporate carbon dioxide from the atmosphere into carbohydrates during photosynthesis. Some algae sink to the lakebed or seafloor, and over millennia, algal cells are converted into natural gas and oil. Similarly, plant material can be buried and converted into coal. These fossilized plants, or fossil fuels, represent a large carbon reservoir. When fossil fuels and plant biomass are burned, carbon dioxide is released from the chemical bonds of these materials and returned to the atmosphere.

Chemically mediated transformations of carbon within the larger carbon cycle described above also occur. Carbon dioxide from the atmosphere can be dissolved into water as carbonate and bicarbonate. Similarly, it can be released from its dissolved form back into the atmosphere. Biologically mediated cycles are also present within the larger carbon cycle. Plants and algae respire carbon dioxide directly into the atmosphere. When an animal consumes a plant, it incorporates the carbon from the plant’s carbohydrates into its own biomolecules. During animal respiration, carbon dioxide is released into the atmosphere.

Some marine organisms incorporate dissolved carbon into their shells. When these organisms die, they sink to the bottom of the ocean and leave their shells behind. Over long periods of time, these shells are transformed into limestone rock. When limestone is uplifted, it becomes land. As the limestone weathers, carbon is returned to the atmosphere and dissolved in water.

Impacts and Issues

Because of industrial dependence on fossil fuels, larger concentrations of carbon dioxide are input to the atmosphere than can be taken up by biologically and chemically mediated transformations. In addition, burning large sections of forests without replanting has released carbon dioxide into the atmosphere and decreased the size of a significant carbon reservoir.

Carbon dioxide has a property that allows it to trap heat. Most scientists agree that the increase in carbon dioxide in the atmosphere has caused an increase in the global temperature and will likely continue to do so for quite some time. Such an increase has significant impacts, including the melting of the polar ice sheets contributing to sea level rise, changes in the patterns and intensity of weather systems, the increased spread of insect-born disease, and challenges for agriculture.

Words to Know

Biosphere: The sum total of all life-forms on Earth and the interaction among those life-forms.

Carbon: Chemical element with atomic number 6. The nucleus of a carbon atom contains 6 protons and from 6 to 8 neutrons. Carbon is present, by definition, in all organic substances; it is essential to life and, in the form of the gaseous compounds CO2 (carbon dioxide) and CH4 (methane), the major driver of climate change.

Fossil Fuels: Fuels formed by biological processes and transformed into solid or fluid minerals over geological time. Fossil fuels include coal, petroleum, and natural gas. Fossil fuels are non-renewable on the timescale of human civilization, because their natural replenishment would take many millions of years.

Hydrosphere: The totality of water encompassing Earth, comprising all the bodies of water, ice, and water vapor in the atmosphere.

Limestone: A carbonate sedimentary rock composed of more than 50% of the mineral calcium carbonate (CaCO3).

Lithosphere: The rigid, uppermost section of Earth’s mantle, especially the outer crust.

Photosynthesis: The process by which green plants use light to synthesize organic compounds from carbon dioxide and water. In the process, oxygen and water are released. Increased levels of carbon dioxide can increase net photosynthesis in some plants. Plants create a very important reservoir for carbon dioxide.

Reservoir: A natural or artificial receptacle that stores a particular substance for a period of time

Transformation: The processes involved in the transfer of a substance from one reservoir to another.



Raven, Peter H., and Linda R. Berg. Environment. Hoboken, NJ: John Wiley and Sons, 2006.

Web Sites:

‘‘Carbon Cycle.’’ Environmental Literacy Council,September 25, 2006. <http://www.enviroliteracy.org/article.php/478.html> (accessed April 5, 2016).

‘‘The Carbon Cycle.’’ NASA’s Earth Observatory.

<http://earthobservatory.nasa.gov/Library/CarbonCycle/> (accessed April 5, 2016).

‘‘Understanding the Global Carbon Cycle.’’ Woods Hole Research Center <http://whrc.org//?s=carbon+cycle&submit=> (accessed April 5, 2016).

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(50) Climate Change

How Carbon Credits Work In Less Than 2 Minutes (Video)

What Are Carbon Credits?

Introduction to Carbon Credits


Carbon Credits

Carbon credits are financial abstractions, similar to money, that entitle their possessor to emit a certain amount of carbon dioxide (CO2) or other greenhouse gases. They are created by governments and bought and sold on emissions trading markets. Participation by polluters in emissions trading markets may be voluntary, as with the Chicago Climate Exchange, or mandatory, as with the European Climate Exchange. The largest system of carbon credits and emissions trading was established by the Kyoto Protocol in 2005.

The term carbon credits is sometimes used interchangeably with the term carbon offsets, but the latter often refers to voluntary purchase by businesses or individuals of decreased CO2 emissions in order to cancel out their own emissions (for example, paying a company to plant trees to cancel out the carbon released by one’s air travel). Offsetting of this kind is not a tradable commodity but a one-time purchase made for reasons of conscience or public relations. It is discussed in the entry ‘‘Offsetting’’ in this set. In this article, only carbon credits that are a tradable commodity in a legally defined emissions trading system are discussed.

Historical Background and Scientific Foundations

In 1992, the United Nations Framework Convention on ClimateChange (UNFCCC)committed all its signatories-virtually every country in the world-to ‘‘formulate, implement, publish and regularly update national and, where appropriate, regional programmes containing measures to mitigate climate change by addressing anthropogenic emissions by sources and removals by sinks.’’ In 1997, to fulfill this earlier commitment, most countries signed the Kyoto Protocol to theUNFCCC.

The Kyoto Protocol defined targets for reduced greenhouse emissions from its industrialized signatories, namely, all the industrialized countries except the United States and Australia. Specifically, industrialized countries signing the protocol agreed to reduce their greenhouse emissions to 5.2% below 1990 levels by 2012. Countries could meet this goal either by actually reducing their emissions or by acquiring carbon credits that represented reductions elsewhere. Kyoto provided three mechanisms by which signatories could obtain carbon credits: joint implementation, the Clean Development Mechanism, and emissions trading. Reductions or removals in one country can count as credits in another country that has paid or traded for them. These credits can be applied toward the receiving country’s emission targets or quotas. For example, if a country is obliged under the protocol to emit no more than 1 million units of carbon but is actually emitting 1.1 million units, it can still meet its treaty obligation by obtaining 100,000 carbon credits through one or more of the following three mechanisms:

Joint implementation: Refers to implementation by a developed country of an emissions-reducing project or sink-enhancing project in another developed country. According to the United Nations, in practice, joint implementation means the building of emissions-reducing projects in countries formerly part of the Soviet Union, termed ‘‘transition economies,’’ using funds from Western European or other industrialized countries. Countries that sponsor projects that reduce emissions or increase uptake by carbon sinks receive credits-the more carbon is kept out of the atmosphere, the more credits are earned.

Clean Development Mechanism: Allows industrialized countries to earn carbon credits by funding projects in developing countries that either lower greenhouse emissions or enhance removals through sinks, particularly through increasing forests.

International emissions trading: Allows Kyoto signatory countries to buy and sell carbon credits internationally. In principle, a country that can keep a ton of carbon out of the atmosphere for less than the market price of a carbon credit can then sell its extra credits to countries for whom reducing emissions is more expensive than buying credits. In this way, emission reductions will happen where they are cheapest and all parties will benefit. The United States is the only industrialized country to have signed but not ratified (agreed formally to abide by) the Kyoto Protocol.

The Kyoto Protocol is an international cap-and-trade scheme. That is, it defines a limit on total emissions by the world’s industrialized economies, then permits trade and transfer of carbon credits so that savings can happen where they are most profitable. The basic unit or tradable credit in all three of these mechanisms is the Kyoto Allocation Allowance Unit (or ‘‘unit’’) and is equivalent to one metric ton (2,204 lb, 1,000 kg) of CO2.

The word ‘‘equivalent’’ means that carbon credits do not necessarily stand only for emissions of CO2. They may represent emissions of other gases, some containing carbon (e.g., methane, CH4) and some not, such as nitrogen-oxygen compounds. Since CO2 is the most important greenhouse gas, accounting for 63% of anthropogenic (human-caused) global warming, it is customary in climate science to translate emissions of non-CO2 gases into the number of tons of CO2 that would create an equal amount of global warming. For example, since methane is 21 times more powerful a greenhouse gas than CO2, the right to emit 1/21 of a ton of methane would be marketed as a single carbon credit.

There are several different species of Kyoto carbon credits:

Assigned amount unit (AAU). Carbon credit issued to a polluter by an Annex I country from its treaty assigned budget of credits. An AAU is, in effect, permission to emit one ton of carbon dioxide.

A removal unit (RMU). Carbon credit issued by an Annex I party for carbon reclaimed from the atmosphere, or not emitted to the atmosphere, by forestry and land-use practices. An operator who keeps one ton of greenhouse gas (carbon equivalent) out of the atmosphere through land use practices may, in effect, be issued the right to emit a ton of gas elsewhere.

Emission reduction unit (ERU). Carbon credit generated by a joint implementation project.

Certified emission reduction (CER). Carbon credit generated by an emissions-reduction project sponsored by an Annex I country in a non-Annex I country such as China.

The Kyoto Protocol is not the only legal setup for defining and trading carbon credits. The European Union and other groups of countries established smaller carbon markets before the protocol entered into force in February 2005. These systems were designed, however, to create regional markets that would link up with the global market defined by the protocol once it became operational, and so define their tradable carbon credits using Kyoto’s terms. As of 2007, carbon credits were being traded on five European exchanges. On the European carbon market, the price of a carbon credit was, in mid-2007, around 20 euros (US$28).

After the ratification of the Kyoto Protocol by Russia in October 2004, the Kyoto-defined trade in carbon credits was forecast by investors in the financial industry to become one of the world’s largest commodity markets, trading somewhere between $60 billion and $250 billion annually by 2008. By mid-2007, the market was still trading only $30 billion, but investment analysts were predicting that it could grow to as much as $1 trillion by 2017.

Impacts and Issues

The Kyoto Protocol has been criticized by most conservatives and libertarians as an ineffectual system for reducing greenhouse-gas emissions. Cap-and-trade schemes defining carbon credits as an international commodity, these critics say, are a form of top-down interference in markets and should be replaced by voluntary schemes that encourage, but do not require, reductions in emissions.

Carbon credits, as well as pollution credits of other kinds, have been criticized by environmentalists and political progressives as granting a right to pollute and so being essentially unethical. The Durban Declaration of 2004, signed by over 150 popular organizations, mostly from undeveloped nations in the global South, states that carbon trading ‘‘turns the Earth’s recycling capacity into property to be bought or sold in a global market.

Through this process of creating a new commodity-carbon-the Earth’s ability and capacity to support a climate conducive to life and human societies is now passing into the same corporate hands that are destroying the climate’’ (quoted in Vallette et al., 2004).

Such critics urge that commodification through carbon credits should be replaced by what they term the ‘‘polluter pays principle,’’ whereby direct taxation or fines would be imposed on emitters in proportion to how much they emit. Carbon taxes are a form of polluter-pays system. Some environmentalists, as well as some fiscal conservatives, have accused the European carbon market and Kyoto global carbon market of being a scam that funnels profits to private investors without significantly reducing greenhouse emissions. These critics charge that emissions caps have been set so high that industries are not actually reducing their emissions significantly, if at all.

Primary Source Connection

In this press release, the Environment Secretary of the United Kingdom discusses a novel proposal under which each citizen of the U.K. would be issued personal carbon allowances. The goal of the plan is to reduce carbon emissions in the U.K. Individuals would have carbon credits deducted from their allowances for any activity that results in carbon emissions. People who exhaust their carbon allowance would be forced to buy credits from other individuals on an open market.


Climate change is a complex problem, which, although environmental in nature, has consequences for all spheres of existence on our planet. It either impacts on– or is impacted by– global issues, including poverty, economic development, population growth, sustainable development and resource management.

At the very heart of the response to climate change, however, lies the need to reduce emissions. In 2010, governments agreed that emissions need to be reduced so that global temperature increases are limited to below 2 degrees Celsius.

UN Framework Convention on Climate Change

In 1992, countries joined an international treaty, theUnited Nations Framework Convention on Climate Change(UNFCCC), to consider what they could do to limit global temperature increases and the resulting climate change, and to cope with its impacts.

By 1995, countries realized that emission reductions provisions in the Convention were inadequate. As a result, they launched negotiations to strengthen the global response to climate change, and, in 1997, adopted the Kyoto Protocol.

The Kyoto Protocollegally binds developed countries to emission reduction targets. The Protocol’s first commitment period started in 2008 and ended in 2012. The second commitment period began on 1 January 2013 and will end in 2020.

There are now 195 Parties to the Convention and 192 Parties to the Kyoto Protocol. The Protocol entered into force on 16 February 2005. Since then, the Protocol  the Parties to the Protocol  have continued the negotiations and have amended the Protocol to achieve more ambitious results by 2030.

The following timeline provides a brief summary of negotiations towards a climate agreement.

Negotiations timeline
1979— The first World Climate Conference takes place.
1988— The Intergovernmental Panel on Climate Change (IPCC) is set up.Learn more about the science of climate change.
1990— The IPCC and the second World Climate Conference call for a global treaty on climate change. The United Nations General Assembly negotiations on a framework convention begin.
1991— First meeting of the Intergovernmental Negotiating Committee takes place.
1992—At the Earth Summit in Rio, the UNFCCC is opened for signature along with its sister Rio Conventions, theUN Convention on Biological Diversityand theUN Convention to Combat Desertification.
 1994— The UNFCCC enters into force.
1995— The first Conference of the Parties (COP 1) takes place in Berlin.
1996— TheUNFCCC Secretariatis set up to support action under the Convention.
1997The Kyoto Protocolis formally adopted in December at COP3.
2001The Marrakesh Accordsare adopted at COP7, detailing the rules for implementation of the Kyoto Protocol, setting up new funding and planning instruments for adaptation, and establishing a technology transfer framework.
2005— Entry into force of the Kyoto Protocol. The first Meeting of the Parties to the Kyoto Protocol (MOP 1) takes place in Montreal. In accordance with Kyoto Protocol requirements, Parties launched negotiations on the next phase of the KP under theAd Hoc Working Group on Further Commitments for Annex I Parties under the Kyoto Protocol (AWG-KP). What was to become theNairobi Work Programme on Adaptation(it would receive its name in 2006, one year later) is accepted and agreed on.
2007— The IPCC’s Fourth Assessment Report is released. Climate science entered into popular consciousness. At COP13, Parties agreed on theBali Road Map, which charted the way towards a post-2012 outcome in two work streams: the AWG-KP, and another under the Convention, known as the Ad-Hoc Working Group on Long-Term Cooperative Action 
2009— Copenhagen Accord drafted at COP15 in Copenhagen. Countries later submitted emissions reductions pledges or mitigation action pledges, all non-binding.
2010Cancun Agreementsdrafted and largely accepted by the COP, at COP16. Through the Agreements, countries made their emission reduction pledges official, in what was the largest collective effort the world has ever seen to reduce emissions in a mutually accountable way.
2011The Durban Platformfor Enhanced Action drafted and accepted by the COP, at COP17. In Durban, governments clearly recognized the need to draw up the blueprint for a fresh universal, legal agreement to deal with climate change beyond 2020, where all will play their part to the best of their ability and all will be able to reap the benefits of success together.
2012– TheDoha Amendmentto the Kyoto Protocol is adopted by the CMP at CMP8. The amendment includes: new commitments for Annex I Parties to the Kyoto Protocol who agreed to take on commitments in a second commitment period from 1 January 2013 to 31 December 2020; a revised list of greenhouse gases to be reported on by Parties in the second commitment period; and amendments to several articles of the Kyoto Protocol pertaining to the first commitment period and which needed to be updated for the second commitment period.
2013– Key decisions adopted at COP19/CMP9 include decisions on further advancing the Durban Platform, the Green Climate Fund and Long-Term Finance, the Warsaw Framework for REDD Plus and the Warsaw International Mechanism for Loss and Damage. More on theWarsaw Outcomes.
2014– COP20 December in Lima, Peru - http://www.cop20lima.org/
2015– COP21 or CMP11 in Paris, France in December. http://www.cop21paris.org/

Words to Know

Annex I and Non-Annex I Countries: Groups of countries defined by the United Nations Framework Convention on Climate Change (UNFCCC) of 1992. Annex I countries are industrialized countries who agreed, under the treaty, to reduce their greenhouse emissions. All non-Annex I countries were developing (poorer, less-industrialized) countries. Annex II countries were wealthy Annex I countries who agreed to help pay for greenhouse reductions by developing (poorer) countries.

Anthropogenic: Made by people or resulting from human activities. Usually used in the context of emissions that are produced as a result of human activities.

CAP and Trade: The practice, in pollution-control or climate mitigation schemes, of mandating an upper limit or cap for the total amount of some substance to be emitted (e.g., CO2) and then assigning allowances or credits to polluters that correspond to fixed shares of the total amount. These allowances or credits can then be bought and sold by polluters, in theory allowing emission cuts to be bought where they are most economically rational.

Carbon Sink: Any process or collection of processes that is removing more carbon from the atmosphere than it is emitting. A forest, for example, is a carbon sink if more carbon is accumulating in its soil, wood, and other biomass than is being released by fire, forestry, and decay. The opposite of a carbon sink is a carbon source.

Carbon Tax: Mandatory fee charged for the emission of a given quantity of CO2 or some other greenhouse gas. Under a carbon taxation scheme, polluters who emit greenhouse gases must pay costs that are directly proportional to their emissions. The purpose of a carbon tax is to reduce greenhouse emissions. Carbon taxation is the main alternative to emissions trading.

Emissions Trading Market: System for trading in carbon credits, money-like units that entitle their owners to emit 1 ton of carbon dioxide or an equivalent amount of some other greenhouse gas. As of 2007, the most important emissions trading market was the European Union Emission Trading Scheme, with mandatory participation for large greenhouse polluters throughout the European Union (trading since 2005); in the United States, a smaller, voluntary market called the Chicago Climate Exchange (trading since 2003).

Greenhouse Gases: Gases that cause Earth to retain more thermal energy by absorbing infrared light emitted by Earth’s surface. The most important greenhouse gases are water vapor, carbon dioxide, methane, nitrous oxide, and various artificial chemicals such as chlorofluorocarbons. All but the latter are naturally occurring, but human activity over the last several centuries has significantly increased the amounts of carbon dioxide, methane, and nitrous oxide in Earth’s atmosphere, causing global warming and global climate change.

Kyoto Protocol: Extension in 1997 of the 1992 United Nations Framework Convention on Climate Change (UNFCCC), an international treaty signed by almost all countries with the goal of mitigating climate change. The United States, as of early 2008, was the only industrialized country to have not ratified the Kyoto Protocol, which is due to be replaced by an improved and updated agreement starting in 2012.



Chameides, William, and Michael Oppenheimer. ‘‘Carbon Trading Over Taxes.’’ Science 315 (2007): 1670.

Kanter, James. ‘‘Carbon Trading: Where Greed Is Green.’’ International Herald Tribune, June 20, 2007.

Web Sites

‘‘Emission Impossible: Access to JI/CDM Credits in Phase II of the EU Emissions Trading Scheme.’’ World Wide Fund for Nature, UK, June 2007.

<http://assets.panda.org/downloads/emission_impossible__final_.pdf> (accessed March 14, 2016).

‘‘Emissions Trading.’’ United Nations Framework Convention on Climate Change Secretariat, June 22, 2007. <http://unfccc.int/kyoto_protocol/mechanisms/emissions_trading/items/2731.php>

 (accessed March 14, 2016).

Vallette, Jim, et al. ‘‘A Wrong Turn from Rio: The World Bank’s Road to Climate Catastrophe.’’ Sustainable Energy and Economy Network, December 2004. <http://sustainable-economy.org/seen/PDFs/Wrong_turn_Rio.pdf>

(accessed March 14, 2016).



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