(A) CLIMATE CHANGE

Climate change, periodic modification of Earth’s climate brought about as a result of changes in the atmosphere as well as interactions between the atmosphere and various other geologic, chemical, biological, and geographic factors within the Earth system.

The atmosphere is a dynamic fluid that is continually in motion. Both its physical properties and its rate and direction of motion are influenced by a variety of factors, including solar radiation, the geographic position of continents, ocean currents, the location and orientation of mountain ranges, atmospheric chemistry, and vegetation growing on the land surface. All these factors change over time. Some factors, such as the distribution of heat within the oceans, atmospheric chemistry, and surface vegetation, change at very short timescales. Others, such as the position of continents and the location and height of mountain ranges, change over very long timescales. Therefore, climate, which results from the physical properties and motion of the atmosphere, varies at every conceivable timescale.

Climate is often defined loosely as the average weather at a particular place, incorporating such features as temperatureprecipitationhumidity, and windiness. A more specific definition would state that climate is the mean state and variability of these features over some extended time period. Both definitions acknowledge that the weather is always changing, owing to instabilities in the atmosphere. And as weather varies from day to day, so too does climate vary, from daily day-and-night cycles up to periods of geologic time hundreds of millions of years long. In a very real sense, climate variation is a redundant expression-climate is always varying. No two years are exactly alike, nor are any two decades, and two centuries, or any two millennia.

This article addresses the concept of climatic variation and change within the set of integrated natural features and processes known as the Earth system. The nature of the evidence for climate change is explained, as are the principal mechanisms that have caused climate change throughout the history of Earth. Finally, a detailed description is given of climate change over many different timescales, ranging from a typical human lifespan to all of the geologic time. For a detailed description of the development of the Earth’s atmosphere, see the article atmosphere, evolution of. For full treatment of the most critical issue of climate change in the contemporary world, see global warming.

The Earth System

The atmosphere is influenced by and linked to other features of Earth, including oceans, ice masses (glaciers and sea ice), land surfaces, and vegetation. Together, they make up an integrated Earth system, in which all components interact with and influence one another in often complex ways. For instance, climate influences the distribution of vegetation on Earth’s surface (e.g., deserts exist in arid regions, forests in humid regions), but vegetation, in turn, influences climate by reflecting radiant energy back into the atmosphere, transferring water (and latent heat) from soil to the atmosphere, and influencing the horizontal movement of air across the land surface.

 

Earth scientists and atmospheric scientists are still seeking a full understanding of the complex feedbacks and interactions among the various components of the Earth system. This effort is being facilitated by the development of an interdisciplinary science called Earth system science. Earth system science is composed of a wide range of disciplines, including climatology (the study of the atmosphere), geology (the study of Earth’s surface and underground processes), ecology (the study of how Earth’s organisms relate to one another and their environment), oceanography (the study of Earth’s oceans), glaciology (the study of Earth’s ice masses), and even the social sciences (the study of human behaviour in its social and cultural aspects).

A full understanding of the Earth system requires knowledge of how the system and its components have changed through time. The pursuit of this understanding has led to development of Earth system history, an interdisciplinary science that includes not only the contributions of Earth system scientists but also paleontologists (who study the life of past geologic periods), paleoclimatologists (who study past climates), paleoecologists (who study past environments and ecosystems), paleoceanographers (who study the history of the oceans), and other scientists concerned with Earth history. Because different components of the Earth system change at different rates and are relevant at different timescales, Earth system history is a diverse and complex science. Students of Earth system history are not just concerned with documenting what has happened; they also view the past as a series of experiments in which solar radiation, ocean currents, continental configurations, atmospheric chemistry, and other important features have varied. These experiments provide opportunities to learn the relative influences of and interactions between various components of the Earth system. Studies of Earth system history also specify the full array of states the system has experienced in the past and those the system is capable of experiencing in the future.

Undoubtedly, people have always been aware of climatic variation at the relatively short timescales of seasons, years, and decades. Biblical scripture and other early documents refer to droughtsfloods, periods of severe cold, and other climatic events. Nevertheless, a full appreciation of the nature and magnitude of climatic change did not come about until the late 18th and early 19th centuries, a time when the widespread recognition of the deep antiquity of Earth occurred. Naturalists of this time, including Scottish geologist Charles Lyell, Swiss-born naturalist and geologist Louis Agassiz, English naturalist Charles Darwin, American botanist Asa Gray, and Welsh naturalist Alfred Russel Wallace, came to recognize geologic and biogeographic evidence that made sense only in the light of past climates radically different from those prevailing today.

Geologists and palaeontologists in the 19th and early 20th centuries uncovered evidence of massive climatic changes taking place before the Pleistocene-that is, before some 2.6 million years ago. For example, red beds indicated aridity in regions that are now humid (e.g., England and New England), whereas fossils of coal-swamp plants and reef corals indicated that tropical climates once occurred at present-day high latitudes in both Europe and North America. Since the late 20th century the development of advanced technologies for dating rocks, together with geochemical techniques and other analytical tools, have revolutionized the understanding of early Earth system history.

The occurrence of multiple epochs in recent Earth history during which continental glaciers, developed at high latitudes, penetrated into northern Europe and eastern North America was recognized by scientists by the late 19th century. Scottish geologist James Croll proposed that recurring variations in orbital eccentricity (the deviation of Earth’s orbit from a perfectly circular path) were responsible for alternating glacial and interglacial periods. Croll’s controversial idea was taken up by Serbian mathematician and astronomer Milutin Milankovitch in the early 20th century. Milankovitch proposed that the mechanism that brought about periods of glaciation was driven by cyclic changes in eccentricity as well as two other orbital parameters: precession (a change in the directional focus of Earth’s axis of rotation) and axial tilt (a change in the inclination of Earth’s axis with respect to the plane of its orbit around the Sun). Orbital variation is now recognized as an important driver of climatic variation throughout Earth’s history (see below Orbital [Milankovitch] variations).

Evidence For Climate Change

All historical sciences share a problem: As they probe farther back in time, they become more reliant on fragmentary and indirect evidence. Earth system history is no exception. High-quality instrumental records spanning the past century exist for most parts of the world, but the records become sparse in the 19th century, and few records predate the late 18th century. Other historical documents, including ship’s logs, diaries, court and church records, and tax rolls, can sometimes be used. Within strict geographic contexts, these sources can provide information on frosts, droughts, floods, sea ice, the dates of monsoons, and other climatic features-in some cases up to several hundred years ago.

Fortunately, climatic change also leaves a variety of signatures in the natural world. Climate influences the growth of trees and corals, the abundance and geographic distribution of plant and animal species, the chemistry of oceans and lakes, the accumulation of ice in cold regions, and the erosion and deposition of materials on Earth’s surface. Paleoclimatologists study the traces of these effects, devising clever and subtle ways to obtain information about past climates. Most of the evidence of past climatic change is circumstantial, so palaeoclimatology involves a great deal of investigative work. Wherever possible, paleoclimatologists try to use multiple lines of evidence to cross-check their conclusions. They are frequently confronted with conflicting evidence, but this, as in other sciences, usually leads to an enhanced understanding of the Earth system and its complex history. New sources of data, analytical tools, and instruments are becoming available, and the field is moving quickly. Revolutionary changes in the understanding of Earth’s climate history have occurred since the 1990s, and coming decades will bring many new insights and interpretations.

Ongoing climatic changes are being monitored by networks of sensors in space, on the land surface, and both on and below the surface of the world’s oceans. Climatic changes of the past 200–300 years, especially since the early 1900s, are documented by instrumental records and other archives. These written documents and records provide information about climate change in some locations for the past few hundred years. Some very rare records date back over 1,000 years. Researchers studying climatic changes predating the instrumental record rely increasingly on natural archives, which are biological or geologic processes that record some aspect of past climate. These natural archives, often referred to as proxy evidence, are extraordinarily diverse; they include but are not limited to, fossil records of past plant and animal distributions, sedimentary and geochemical indicators of former conditions of oceans and continents, and land surface features characteristic of past climates. Paleoclimatologists study these natural archives by collecting cores, or cylindrical samples, of sediments from lakesbogs, and oceans; by studying surface features and geological strata; by examining tree-ring patterns from cores or sections of living and dead trees; by drilling into marine corals and cave stalagmites; by drilling into the ice sheets of Antarctica and Greenland and the high-elevation glaciers of the Plateau of Tibet, the Andes, and other montane regions; and by a wide variety of other means. Techniques for extracting paleoclimatic information are continually being developed and refined, and new kinds of natural archives are being recognized and exploited.

Causes Of Climate Change

It is much easier to document the evidence of climate variability and past climate change than it is to determine their underlying mechanisms. Climate is influenced by a multitude of factors that operate at timescales ranging from hours to hundreds of millions of years. Many of the causes of climate change are external to the Earth system. Others are part of the Earth system but external to the atmosphere. Still, others involve interactions between the atmosphere and other components of the Earth system and are collectively described as feedbacks within the Earth system. Feedbacks are among the most recently discovered and challenging causal factors to study. Nevertheless, these factors are increasingly recognized as playing fundamental roles in climate variation. The most important mechanisms are described in this section.

Solar variability

The luminosity, or brightness, of the Sun, has been increasing steadily since its formation. This phenomenon is important to Earth’s climate because the Sun provides the energy to drive atmospheric circulation and constitutes the input for Earth’s heat budget. Low solar luminosity during Precambrian time underlies the faint young Sun paradox, described in the section Climates of early Earth.

Radiative energy from the Sun is variable at very small timescales, owing to solar storms and other disturbances, but variations in solar activity, particularly the frequency of sunspots, are also documented at decadal to millennial timescales and probably occur at longer timescales as well. The “Maunder minimum,” a period of drastically reduced sunspot activity between AD 1645 and 1715, has been suggested as a contributing factor to the Little Ice Age. (See below Climatic variation and change since the emergence of civilization.)

Volcanic activity

Volcanic activity can influence climate in a number of ways at different timescales. Individual volcanic eruptions can release large quantities of sulfur dioxide and other aerosols into the stratosphere, reducing atmospheric transparency and thus the amount of solar radiation reaching Earth’s surface and troposphere. A recent example is the 1991 eruption in the Philippines of Mount Pinatubo, which had measurable influences on atmospheric circulation and heat budgets. The 1815 eruption of Mount Tambora on the island of Sumbawa had more dramatic consequences, as the spring and summer of the following year (1816, known as “the year without a summer”) were unusually cold over much of the world. New England and Europe experienced snowfalls and frosts throughout the summer of 1816.

Volcanoes and related phenomena, such as ocean rifting and subduction, release carbon dioxide into both the oceans and the atmosphere. Emissions are low; even a massive volcanic eruption such as Mount Pinatubo releases only a fraction of the carbon dioxide emitted by fossil-fuel combustion in a year. At geologic timescales, however, a release of this greenhouse gas can have important effects. Variations in carbon dioxide released by volcanoes and ocean rifts over millions of years can alter the chemistry of the atmosphere. Such changeability in carbon dioxide concentrations probably accounts for much of the climatic variation that has taken place during the Phanerozoic Eon. (See below Phanerozoic climates.)

Tectonic activity also influences atmospheric chemistry, particularly carbon dioxide concentrations. Carbon dioxide is emitted from volcanoes and vents in rift zones and subduction zones. Variations in the rate of spreading in rift zones and the degree of volcanic activity near plate margins have influenced atmospheric carbon dioxide concentrations throughout Earth’s history. Even the chemical weathering of rock constitutes an important sink for carbon dioxide. (A carbon sink is any process that removes carbon dioxide from the atmosphere by the chemical conversion of CO2 to organic or inorganic carbon compounds.) Carbonic acid, formed from carbon dioxide and water, is a reactant in the dissolution of silicates and other minerals. Weathering rates are related to the mass, elevation, and exposure of bedrock. Tectonic uplift can increase all these factors and thus lead to increased weathering and carbon dioxide absorption. For example, the chemical weathering of the rising Tibetan Plateau may have played an important role in depleting the atmosphere of carbon dioxide during a global cooling period in the late Cenozoic Era. (See below Cenozoic climates.)

Orbital (Milankovich) variations

These orbital variations cause changes in the latitudinal and seasonal distribution of solar radiation, which in turn drive a number of climate variations. Orbital variations play major roles in pacing glacial-interglacial and monsoonal patterns. Their influences have been identified in climatic changes over much of the Phanerozoic. For example, cyclothems-which are an interbedded marine, fluvial, and coal beds characteristic of the Pennsylvanian Subperiod (318.1 million to 299 million years ago)-appear to represent Milankovitch-driven changes in mean sea level.

Greenhouse gases

Greenhouse gases are gas molecules that have the property of absorbing infrared radiation (net heat energy) emitted from Earth’s surface and reradiating it back to Earth’s surface, thus contributing to the phenomenon known as the greenhouse effect. Carbon dioxide, methane, and water vapour are the most important greenhouse gases, and they have a profound effect on the energy budget of the Earth system despite making up only a fraction of all atmospheric gases. Concentrations of greenhouse gases have varied substantially during Earth’s history, and these variations have driven substantial climate changes at a wide range of timescales. In general, greenhouse gas concentrations have been particularly high during warm periods and low during cold phases. A number of processes influence greenhouse gas concentrations. Some, such as tectonic activities, operate at timescales of millions of years, whereas others, such as vegetation, soil, wetland, and ocean sources and sinks, operate at timescales of hundreds to thousands of years. Human activities-especially fossil-fuel combustion since the Industrial Revolution-are responsible for steady increases in atmospheric concentrations of various greenhouse gases, especially carbon dioxide, methane, ozone, and chlorofluorocarbons (CFCs).

 

Feedback

Perhaps the most intensively discussed and researched topic in climate variability is the role of interactions and feedbacks among the various components of the Earth system. The feedbacks involve different components that operate at different rates and timescales. Ice sheets, sea ice, terrestrial vegetation, ocean temperatures, weathering rates, ocean circulation, and greenhouse gas concentrations are all influenced either directly or indirectly by the atmosphere; however, they also all feedback into the atmosphere, thereby influencing it in important ways. For example, different forms and densities of vegetation on the land surface influence the albedo, or reflectivity, of Earth’s surface, thus affecting the overall radiation budget at local to regional scales. At the same time, the transfer of water molecules from soil to the atmosphere is mediated by vegetation, both directly (from transpiration through plant stomata) and indirectly (from shading and temperature influences on direct evaporation from soil). This regulation of latent heat flux by vegetation can influence climate at local to global scales. As a result, changes in vegetation, which are partially controlled by climate, can in turn influence the climate system. Vegetation also influences greenhouse gas concentrations; living plants constitute an important sink for atmospheric carbon dioxide, whereas they act as sources of carbon dioxide when they are burned by wildfires or undergo decomposition. These and other feedbacks among the various components of the Earth system are critical for both understanding past climate changes and predicting future ones.

 

Human activities

Recognition of global climate change as an environmental issue has drawn attention to the climatic impact of human activities. Most of this attention has focused on carbon dioxide emission via fossil-fuel combustion and deforestation. Human activities also yield releases of other greenhouse gases, such as methane (from rice cultivation, livestock, landfills, and other sources) and chlorofluorocarbons (from industrial sources). There is little doubt among climatologists that these greenhouse gases affect the radiation budget of Earth; the nature and magnitude of the climatic response are a subject of intense research activity. Paleoclimate records from tree rings, coral, and ice cores indicate a clear warming trend spanning the entire 20th century and the first decade of the 21st century. In fact, the 20th century was the warmest of the past 10 centuries, and the decade 2001–10 was the warmest decade since the beginning of modern instrumental record keeping. Many climatologists have pointed to this warming pattern as clear evidence of human-induced climate change resulting from the production of greenhouse gases.

The second type of human impact, the conversion of vegetation by deforestation, afforestation, and agriculture, is receiving mounting attention as a further source of climate change. It is becoming increasingly clear that human impacts on vegetation cover can have local, regional, and even global effects on climate, due to changes in the sensible and latent heat flux to the atmosphere and the distribution of energy within the climate system. The extent to which these factors contribute to recent and ongoing climate change is an important, emerging area of study.

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(60) Climate Change

Theories of Geological Evolution: Catastrophism vs Uniformitarianism

Catastrophism

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Catastrophism

Catastrophism is the general concept that the history of Earth has been profoundly affected by sudden violent events. In the Biblical creationist view, these sudden, violent events are typically viewed as supernatural in origin and are global events of great devastation. In the modern holistic view of Earth history, catastrophism is viewed as the concept that sudden, violent, but entirely explicable events have occurred in Earth’s past and may have had an effect upon the rock and fossil record of Earth. In this view, a catastrophe may have been, for instance, a colossal volcanic eruption, a comet or asteroid impact on Earth, the burst of a large glacial lake’s dam, or a very powerful earthquake.

Catastrophism stands in contrast to a long-standing but somewhat simplistic view of geology, that Earth processes were more nearly uniform and gradual over geologic time (uniformitarianism). Careful geological research in many subfields of geology over many decades has shown that geological history may be characterized by episodes of uniform and gradual conditions, which in turn are punctuated by episodes with relatively sudden, violent events. In other words, the notion of catastrophes in Earth history is a sound one, but the notion that Earth history is largely one of profound catastrophe is not correct.

Historical Background and Scientific Foundations

Catastrophism as a point of view in geology was founded in the nineteenth century during a time when it was popular to invoke Biblical, supernatural explanations for geological features that were confounding to practitioners of the infant science of geology. One of the first generalizations coming out of catastrophism was the notion of a Biblical flood-related origin for such things as the separation of the continents, mass mortality in the fossil record, glacial erratic boulders and other features, and some aspects of inter-regionally distributed rock formations. Catastrophism was generally closely associated with a young-Earth viewpoint, specifically that Earth was not more than a few thousand years old.

Therefore, in order for the many features we see to exist, they must have all developed in a short time span, hence catastrophes as the key to understanding Earth history. With the advent of the view of deep time (or vast geological history), an opposing viewpoint called uniformitarianism emerged. In this contrary view, Earth history is gradual and changes are uniform with time. The view of uniformitarianism was intended more as a counterpoint to catastrophism but was taken quite literally for many decades. Today, both gradual and catastrophic origins of features and rock formations are embraced by geologists according to the interpretations of those features and rock formations warranted by the facts at hand. 

Catastrophism and the Fossil Record Some nineteenth-century palaeontologists (scientists who study fossils) who were also catastrophists thought that episodes of mass extinction of fossil groups showed evidence of supernatural catastrophes. Today, we understand that some fossil groups disappeared over relatively short intervals of geologic time, but in each instance, we can see evidence of readily explainable causes. Further, careful study shows that even the most seemingly instantaneous extinction event probably occurred over hundreds or perhaps thousands of years, thus showing that these apparent catastrophes were not so sudden. Over the evolutionary history of many fossil groups, it can be shown that the development of new species and the death of other ones is relatively sudden (but not instantaneous). This is called punctuated gradualism in evolution and is thought to be the result of rapid shifts in the fossil group’s environment.

Impacts and Issues

Modern catastrophism is held by many creationists and others who hold to what they consider to be a fundamentalist view of Earth history. For example, in the modern catastrophist view held by creationists, Earth history can be divided into pre-flood and post-flood epochs. All of Earth history is divided according to one catastrophic event. Modern catastrophists also hold to the young-Earth view that all of Earth history occurred in a few thousand years. In this sense, most of Earth’s history had to be sudden and violent, or Earth had to be formed as we know it without any significant evolutionary history. From a catastrophist point of view, the rapidity of modern climate change on Earth would be viewed as supporting evidence of interpreted climate changes in Earth’s past that may have been relatively rapid. That modern climate change is relatively rapid is a view that is not out of step with modern scientific understandings.

Words To Know

Epoch: Unit of geological time. From longest to shortest, the geological system of time units is aeon, era, period, epoch, and stage. Epochs are generally about 500 million years in length.

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

Uniformitarianism: Doctrine of geology promoted by English geologist Charles Lyell (1797–1895), asserting three assumptions: (1) actualism (uniform processes acting throughout Earth’s history), (2) gradualism (slow, uniform rate of change throughout Earth’s history), and (3) uniformity of state (Earth’s conditions have always varied around a single, steady state). Uniformitarianism is often contrasted to catastrophism. Modern geology makes use of elements of both views, acknowledging that change can be drastic or slow and that while some processes operate steadily over many millions of years, others (such as asteroid impacts) may happen rarely and cause catastrophic, sudden changes when they do.

Bibliography:

Books:

Palmer, T. Catastrophism, Neocatastrophism and Evolution. Nottingham, UK: Nottingham Trent University, 1994.

Rudwick, M. J. S. The Meaning of Fossils. Chicago: University of Chicago Press, 1972.

Web Sites:

Baker, Victor. ‘‘Catastrophism and Uniformitarianism: Logical Roots and Current Relevance in Geology.’’ Geological Society of London, 1998. <http://sp.lyellcollection.org/cgi/content/abstract/143/1/171> (accessed March 12, 2018).

 

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(59) Climate Change

What’s a carbon tax?

carbon tax

Carbon Tax

A carbon tax is a levy on sources that emit carbon dioxide (CO2) into the atmosphere. The purpose is to place a financial disincentive on carbon-emitting activities and encourage investment in cleaner technologies and practices. Although no internationally levied carbon tax is in operation, several nations apply variants of this pollution tax.

Historical Background and Scientific Foundations

On January 1, 1991, Sweden became the first country to implement a carbon tax, when it introduced a levy of 0.25 SEK/kg (approximately 0.11c/kg) on the use of carbon-based fuels used in domestic travel. A rate of 0.125 SEK/kg was placed on the use of such fuels

by Swedish industry. Other countries-such as Finland, Norway, the Netherlands, and the United Kingdom-have since implemented their own variants of a carbon tax.

The economic principles underlying a carbon tax are simple. By placing an economic disincentive on carbonemitting activity, primarily the burning of fossil fuels, it simultaneously discourages the discharge of CO2 into Earth’s atmosphere, while encouraging technological innovation to both reduce CO2 and provide an alternative energy to carbon-based fuels.

Impacts and Issues

A lack of international consensus on the efficacy of carbon taxes remains the main reason they are not more ubiquitous. Some argue that unless applied more universally, individual governments likely remain reluctant to place the additional economic burden of carbon taxation on domestic industries and businesses, claiming that foreign competitors not subject to a carbon tax in their home nations would gain an economic advantage.

Others assert that the selective carbon taxes should target only the heaviest polluters-often industries with relatively high margins of profit, such as fossil fuel companies.

Supporters of carbon taxes maintain that they are essential to reduce emissions in order to prevent atmospheric concentrations of CO2 from reaching an irreversible ‘‘tipping point.’’ They assert that internationally applied carbon taxes would help transform the planet’s fossil fuels-based energy system to reliance on energy efficiency, renewable energy, and sustainable fuels. It also encourages ‘‘green’’ innovation in other areas. A significant share of opposition to carbon taxes stems from business and industrial interests. Critics note the additional cost burden placed on businesses, also the lack of viability without an international framework. Unless all countries adopt a carbon tax, it places polluting nations in an economically advantageous position; doubly penalizing business rivals elsewhere that are compelled to pay a carbon tax.

The Swedish experience shows some of the difficulties of maintaining a carbon tax when other countries refrain from introducing such a levy. From the outset, Swedish businesses, already subject to relatively high taxation, complained that a carbon tax lessens their competitiveness in the marketplace. As a concession, the tax was halved for Swedish businesses, and halved again during the financial recession of the mid-1990s. A further concession fully exempted certain high energy using industries such as commercial horticulture, mining, manufacturing, and the paper industry.

The environmental benefits of Sweden’s carbon tax are mixed. Annual CO2 emissions have fallen only slightly since 1990. Because energy costs represent a relatively small percentage of a businesses’ total costs, companies were slow to modify or upgrade existing plants as a result of the new taxes. On the other hand, carbon taxes have prompted technical innovation, for example in the home-heating industry. Sweden is now a world leader in the manufacture of biomass and geothermal energy products. This has not just helped reduce domestic carbon emissions, but has created a new export industry and economic boon.

Bibliography:

Periodicals

Mankiw, N. Gregory. ‘‘One Answer to Global Warming: A New Tax.’’ The New York Times (September 16, 2007).

Web Sites

‘‘Carbon Taxes: An Introduction.’’ Carbon Tax Center. <http://www.carbontax.org/introduction/#what> (accessed December 28, 2017).

‘‘Emission Possible.’’

The Age, June 17, 2007. <http://www.theage.com.au/news/in-depth/emissionpossible/2007/06/17/1182018934799.html?page=fullpage#contentSwap2>

; (accessed December 28, 2017).

Frank, Robert H. ‘‘A Way to Cut Fuel Consumption That Everyone Likes, Except the Politicians.’’ The New York Times, February 16, 2006. <http://query.nytimes.com/gst/fullpage.html?res=9D05E7DA133EF935A25751C0A9609C8 B63> (accessed December 28, 2017).

Words to Know

Biomass: The sum total of living and once-living matter contained within a given geographic area. Plant and animal materials that are used as fuel sources.

Carbon-Based Fuel: Any substance composed mostly of carbon that is burned or otherwise chemically reacted to release energy. Most biofuels and all fossil fuels are carbon based, although natural gas also contains a significant fraction of its energy in the form of hydrogen.

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.

Renewable Energy: Energy obtained from sources that are renewed at once, or fairly rapidly, by natural or managed processes that can be expected to continue indefinitely. Wind, sun, wood, crops, and waves can all be sources of renewable energy.

Tipping Point: In climatology, a state in a changing system where change ceases to be gradual and reversible and becomes rapid and irreversible. Also termed a climate

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(58) Climate Change

The ocean, a carbon sink

What is a Carbon Sink?

What are carbon sinks?

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Carbon Sinks

A carbon sink is any system, natural or artificial, that takes carbon out of the atmosphere. As of the early 2000s, artificial carbon sequestration schemes were still only in the testing and study stage. This article is concerned only with natural carbon sinks.

Carbon is removed from the atmosphere by two basic mechanisms, namely: 1) photosynthesis by green plants, which obtain carbon with which to build their tissues by breaking up carbon dioxide (CO2) molecules in the air releasing the O2; and 2) absorption of CO2 by the oceans. Natural carbon sinks remove slightly more than half of the carbon from the atmosphere that is placed there every year by the burning of fossil fuels.

Scientists refer to two sinks, the land sink and the ocean sink. The land sink consists of green plants, while the ocean sink consists of direct absorption of CO2 by ocean water and secondary absorption by organisms living in the sea followed by transport of the carbon in the dead organisms to deep waters or the ocean floor.

Anthropogenic (human-caused) climate change would be much greater today if it were not for natural carbon sinks. However, human activities are imperiling the efficacy of carbon sinks. The more CO2 the oceans absorb, the more slowly they absorb CO2. Also, ozone, a common air pollutant, decreases the ability of green plants to act as carbon sinks, while cutting down forests and replacing them with other land uses (such as farmland) removes acreage from the land sink.

Historical Background and Scientific Foundations

Several hundred millions of years ago, large amounts of carbon were removed from Earth’s atmosphere by large swamp forests and by tiny organisms floating in the seas. Some of the dead swamp growth accumulated in thick blankets, was covered by other sediments, and was eventually transformed into coal by geological processes. Some of the dead ocean organisms drizzled to the bottom of the sea, were buried, and were eventually transformed into oil and natural gas. These billions of tons of ancient carbon, which were collected at a time when atmospheric CO2 was far higher than today, are now being returned to Earth’s atmosphere in the space of only a few centuries. Human beings are adding about 29.7 billion tons (27 billion metric tons) of CO2 to the atmosphere every year, and the rate is increasing. The two major sources of CO2 in the modern atmosphere are fossil-fuel burning and land-use changes, especially the cutting down of forests.

Starting in the late 1950s, American geochemist Charles David Keeling (1928-2005) was the first scientist to measure the steadily increasing concentration of CO2 in Earth’s atmosphere. Keeling found that CO2 decreases during the growing season in the Northern Hemisphere, where most of the world’s vegetation- its land sink-is located. In the spring and summer, growing plants remove CO2 from the air, while in the winter, plant decay and fuel burning release more CO2 than is absorbed. The result is a series of saw tooth spikes in atmospheric CO2 concentration on top of a steadily rising line that reflects increasing average CO2 concentration.

Thanks to natural carbon sinks, the rate at which CO2 is increasing is about half of what it would be if all the CO2 being added to the atmosphere by human beings was staying there. What is more, as the amount of CO2 released by human activities has grown, tripling from about 1950 to the present, the amount taken up by sinks has grown proportionally. The whole global system of carbon sources and sinks, which is continuously releasing and absorbing carbon around the globe, is termed the carbon cycle. Carbon sinks are only one part of the carbon cycle.

The global carbon-sink picture is difficult to characterize. The atmosphere itself is the only reservoir of carbon that is easy to study, because it is so well-mixed that an air sample taken anywhere on Earth’s surface gives information about global conditions. In contrast, the upper and lower layers of the ocean mix slowly-water in the deepest parts of the North Pacific has been out of contact with the atmosphere for about 1,000 years-and the composition of the ocean is not uniform around the globe. As a result, many thousands of measurements must be taken at various depths and around the world to characterize the carbon content of the oceans. Determining how much carbon goes where is even more difficult in the case of the land sink, which changes constantly and varies over different climates and landscapes.

Ocean Sink

In the early 2000s, about a third of annual anthropogenic carbon emissions were being absorbed by the ocean sink. The ocean sink has two components: the biological pump and the solubility pump. Each component transfers or pumps CO2 out of the atmosphere.

The biological pump consists of tiny marine organisms, both plants and animals, which incorporate carbon into their tissues and shells and then die, sinking to deeper waters. There they either decompose, in which case their carbon is dissolved in deep waters, or settle to the bottom as sediment, where their carbon may remain isolated from the atmosphere for much longer.

The solubility pump is driven by the overturning global circulation of the oceans. Surface waters move toward the polar regions, cooling as they go. As they cool, they become capable of absorbing more CO2 from the atmosphere. Near the poles, they sink and begin to journey back toward the tropics along the ocean floor.

Eventually, after as many as 1,500 years, the water rises to the surface in the tropics and is heated. When heated, the water gives up CO2 to the atmosphere again. The Southern Ocean, the ring-shaped body of water

that surrounds Antarctica south of 60º south latitude, accounts for about half of all absorption by the oceans, that is, about 15% of annual anthropogenic carbon releases.

Land Sink

The land sink is about the same size as the ocean sink, but there are many uncertainties about its size and nature. For decades, most scientists assumed that the land sink’s increasing uptake of CO2 was being driven by the fertilizing effect of increased CO2 in the atmosphere (most plants grow faster when there is more CO2). However, in the early 2000s, studies of forest growth in the United States showed that this fertilization effect was far too small to account for the large size of the land sink in North America. In the United States, at least, it now seems more likely that the regrowth of abandoned farmland and formerly logged lands probably accounts for the relatively large size of the land carbon sink. Increased tree growth in areas where forest fires have been suppressed also contributes.

More than half the total (land plus ocean) sink for anthropogenic carbon is in the Northern Hemisphere, and most of this northern-hemispheric sink is terrestrial (on land). Partly due to global warming, which has made for longer growing seasons, the amount of carbon being taken up by the terrestrial biosphere increased from about 220 million tons (200 million metric tons) per year in the 1980s, with large uncertainty, to about 1.5 billion tons (1.4 billion metric tons) per year in the 1990s.

Impacts and Issues

Despite the enhancement of the land carbon sink in the 1980s and 1990s due to longer growing seasons, scientists predict that the negative effects of climate change on the land biosphere will soon be dominant, and that global warming will slow CO2 uptake by both the ocean and land carbon sinks. This will increase the fraction of anthropogenic CO2 that remains in the atmosphere, making climate change more severe and rapid, other factors being equal.

The global scientific consensus as expressed in 2007 by the United Nations’ Intergovernmental Panel on Climate Change (IPCC) is that it is more than 90% likely that terrestrial ecosystems will become net sources of CO2 between 2050 and 2100. That is, the land carbon sink will shrink, and land-based carbon sources, such as deforestation, will grow until they are emitting more CO2 than the land sink is absorbing. Deforestation, higher temperatures, and shifts in rainfall patterns will all contribute to the shrinkage of the land sink. Ozone (O3) pollution is also reducing the efficacy of the land sink by slowing plant growth. The ocean sink will slow its absorption of carbon as the amount of CO2 dissolved in the water increases and lowers the water’s ability to take up still more CO2. In 2007, an international science team announced that the Southern Ocean’s absorption of CO2 has decreased by about 15% per decade since 1981. This decrease was caused by global climate change, but not (yet) by increased carbon dissolved in the ocean; rather, increased wind strength due to climate shifts was the cause, altering ocean mixing patterns and decreasing carbon uptake.

Primary Source Connection

Forests, prairies, marshlands, and other densely vegetated areas that compose ‘‘carbon sinks’’ help Earth reabsorb carbon dioxide. John Roach, a correspondent for National Geographic News, reports on new research on the North American carbon sink and why it may not help offset human-made emissions in the future.

STUDIES MEASURE CAPACITY OF ‘CARBON SINKS.’

After years of wide disagreement, scientists are getting a better grip on how much carbon Earth’s forests and other biological components suck out of the atmosphere, thus acting as ‘‘carbon sinks.’’ New research in this area may be highly useful in efforts to devise international strategies to address global warming.

The emission of carbon dioxide from the combustion of fossil fuels is the leading cause of the buildup of greenhouse gases in the atmosphere, which many people believe is the main culprit behind an increase in Earth’s temperatures.

For a long time, scientists have known that forests, crops, soils, and other organic matter soak up some of that carbon, thereby slowing down the rate of global warming. Yet their calculations of how much carbon is absorbed have differed, in some cases significantly. A team of scientists led by Stephen Pacala, a professor of ecology and evolutionary biology at Princeton University in New Jersey, set out to resolve this discrepancy in calculations. Their research is reported in the June 22 issue of Science.

Different Measuring Techniques

While some carbon is absorbed by organic matter such as trees and shrubs, carbon is also regularly emitted into the atmosphere by activities on land such as the burning of fossil fuels. Researchers’ lack of agreement on how much carbon is ‘‘stored’’ has been rooted in the use of two different methods of measurement—one atmosphere based, the other land based.

The first method involves measuring concentrations of carbon dioxide in the air as the air moves across landmasses from Point A to Point B. The second method entails making an inventory of all the carbon in a given area of ground and calculating the difference between the levels of carbon recorded from year to year. Although there is wide variation among different atmospheric models of carbon measurement, their results have consistently indicated that higher levels of carbon are absorbed than the land-based models show. Pacala said his team’s land-based analysis was more thorough than earlier studies. ‘‘We did the first exhaustive analysis of the land sink,’’ he said. Previous land-based models inventoried mainly the amount of carbon absorbed by trees, he explained. He and his colleagues included measures of carbon absorbed by landfills, soils, houses, and even silt at the bottom of reservoirs.

‘‘We found out that the land sink was bigger than had been reported by other analyses, about twice as big, and the atmosphere [models] gave numbers that were consistent,’’ he said.

The researchers used their results to help answer a major question that has been a subject of much contention: How big is the entire ‘‘carbon sink’’ of the continental United States?

According to their findings, the scientists estimate that U.S. forests and other terrestrial components absorb from one-third to two-thirds of a billion tons of carbon each year.

At the same time, reliable figures indicate that the United States emits more than two to four times that amount of carbon each year, about 1.4 billion tons. Taking into account the carbon sink effect, 800 million to 1.1 billion tons of carbon accumulates annually in the atmosphere, the researchers say. This refutes the idea that the U.S carbon sink is big enough to equal the amount of carbon that U.S. factories emit through the burning of fossil fuels, as some studies have concluded. The results of the Princeton-led study are particularly interesting because the 23 scientists who participated in the research and agreed on the conclusions initially held strongly differing views about the size of the U.S. carbon sink.

Diminishing Effect

Pacala and his colleagues say the main reason the United States is drawing in a large volume of carbon is because many forests and areas of land that were logged or converted to agriculture in the last 100 years are now recovering with the growth of new vegetation.

These trees and shrubs absorb carbon dioxide from the air and channel it into the growth of massive tree trunks, branches, and foliage. This, in turn, gradually expands the overall size of the U.S. carbon sink. Pacala emphasizes, however, that the U.S. absorption of carbon does not fully offset the emissions of carbon from fossil fuels and should not be seen as a license to release more carbon. A large part of the current sink effect, he said, is the land re-absorbing large quantities of carbon that were released during heavy farming and logging of the past.

‘‘When we chopped down the forests, we released carbon trapped in the trees into the atmosphere. When we plowed up the prairies, we released carbon from the grasslands and soils into the atmosphere,’’ said Pacala. ‘‘Now the ecosystem is taking some of that back.’’ But, he added, the sink effect will steadily decrease and eventually disappear-as U.S. ecosystems complete their recovery from past land use.

‘‘The carbon sinks are going to decrease at the same time as our fossil fuel emissions increase,’’ he said. ‘‘Thus, the greenhouse problem is going to get worse faster than we expected.’’

Carbon Sink in China

In a separate study in Science, researchers reported on a similar carbon sink effect in China, which they attribute to the regrowth of logged forests and intensive planting of new forests. Jingyun Fang, an ecology professor at Peking University in Beijing, and his colleagues noted that Chinese forests were heavily exploited from 1949 to the end of the 1970s. Since then, however, the government has undertaken wide-scale forest planting and reforestation, mainly to combat erosion, flooding, desertification, and loss of biodiversity. An unintended consequence of this increase in vegetation was the growth of a carbon sink that is estimated to be on par with that of North American forests.

ROACH, JOHN. ‘‘STUDIES MEASURE CAPACITY OF ‘CARBON SINKS.’’’ NATIONAL GEOGRAPHIC NEWS, JUNE 21, 2001.

Words to Know

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.

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

Deforestation: Those practices or processes that result in the change of forested lands to non-forest uses. This is often cited as one of the major causes of the enhanced greenhouse effect for two reasons: 1) the burning or decomposition of the wood releases carbon dioxide; and 2) trees that once removed carbon dioxide from the atmosphere in the process of photosynthesis are no longer present and contributing to carbon storage.

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.

Ozone: An almost colorless, gaseous form of oxygen with an odor similar to weak chlorine. A relatively unstable compound of three atoms of oxygen, ozone constitutes, on average, less than one part per million (ppm) of the gases in the atmosphere. (Peak ozone concentration in the stratosphere can get as high as 10 ppm.) Yet ozone in the stratosphere absorbs nearly all of the biologically damaging solar ultraviolet radiation before it reaches Earth’s surface, where it can cause skin cancer, cataracts, and immune deficiencies, and can harm crops and aquatic ecosystems.

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.

Bibliography

Periodicals

Baker, David F. ‘‘Reassessing Carbon Sinks.’’ Science 316 (2007): 1708-1709.

Field, Christopher B., and Inez Y. Fung. ‘‘The Not-So-Big U.S. Carbon Sink.’’ Science 285 (1999): 544-545.

Hopkin, Michael. ‘‘Carbon Sinks Threatened by Ozone.’’ Science 448 (2007): 396-397.

Kaiser, Jocelyn. ‘‘Soaking Up Carbon in Forests and Fields.’’ Science 290 (2000): 922.

Martine, Philippe, et al. ‘‘Carbon Sinks in Temperate Forests.’’ Annual Review of Energy and the Environment 26 (2001): 435-465.

Reay, Dave, et al. ‘‘Spring-time for Sinks.’’ Nature 446 (2007): 727-728.

Wofsy, Steven. ‘‘Where Has All the Carbon Gone?’’ Science 292 (2001): 2261-2263.

Web Sites

Sarmiento, Jorge, and Nicolas Gruber. ‘‘Sinks for Anthropogenic Carbon.’’ Physics Today, August, 2002.

<https://www.aip.org/aip/search?cx=004445072414534619134%3Avptvposetya&q_ry=Sinks+for+Anthropogenic+Carbon&cof=FORID%3A11&searchaip=Search> (accessed November 7, 2017).

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(57) Climate Change

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

 What Is CO2 Sequestration?

CarbonSequestration 

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.

Technologies

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.

Other

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.

Capture

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.

Transport

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.

EPA. ‘‘GEOLOGIC SEQUESTRATION.

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

 NOVEMBER 29, 2007).

Bibliography:

Periodicals

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 CALCULATOR

cf

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.

Bibliography

Periodicals

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

CO2 EQUIVALENTS

co2-graphic

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.

Bibliography:

Books:

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).

IPCC SCIENCE BASIS TECHNICAL SUMMARY

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:

Books:

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.

Periodicals:

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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