(36) Global Warming

Climate Change 2014: Impacts, Adaptation, and Vulnerability - IPCC (Video)

COP 20 - Lima - Peru

Climate Change - UNEP

Fifth Assessment Report (AR5)

ClimateChangeImpacts

Impacts of Climate Change

The IPCC has indicated that climate changes currently taking place most likely will affect the following key areas.

WATER

Close to 70 percent of the earth’s surface is covered with water, but only 1 percent of that water is drinkable. During this century, freshwater availability is expected to increase away from the equator and in some tropical regions by 10-40 percent. However, water will be less available where it is needed the most—in countries closer to the equator.

Water supplies fed by melting glaciers and snow cover, after an initial surge, will begin to dwindle. One-sixth of the world’s population currently relies on melt water from major mountain ranges. As glaciers melt, some water supplies will have abundance, if not an oversupply, of freshwater for a while. However, once the alpine snow cover melts, alternative sources of water will be needed in those areas. Water shortages are anticipated to be a major challenge to many parts of the world. Unless the world adapts to these changes, the water shortages could lead to economic disruption and conflict.

DROUGHTS AND FLOODS

A warmer planet is more prone to both droughts and floods. Since 1950, the number of heat waves around the world has increased. Drought is characterized by a combination of precipitation and temperature conditions. There has been a drying trend since the mid-1950s over specific land areas, including Africa, southern Europe, southern Asia, Canada, and Alaska. Increased global temperatures lead to increased evaporation but also to an increased capacity of the atmosphere to hold water vapor. Climate data are not showing an overall global increase in precipitation. However, there is a statistical increase in the overall number of heavy precipitation events.

ECOSYSTEMS

The earth is, in many ways, forgiving of the abuses that people have subjected it to. However, we may be approaching a point where we will exceed the earth’s ability to recover. If increases in average global temperatures start to increase by 1.5–2.5°C (2.7–4.5°F), many more plant and animal species face a greater risk of extinction. 

Some consequences of global warming no doubt will favor the survival of certain species, but the overall impact is to reduce the biodiversity of the earth. The decreasing pH level of the oceans (becoming more acidic) is likely to affect aquatic organisms that form shells, such as coral or other shellfish. This, in turn, will affect species that depend on the shell-forming organisms. A sea surface temperature increase of greater than 1°C (1.8°F) may be enough to initiate the destruction of coral reefs.

COASTAL AREAS

Many millions more people are projected to be exposed to flood conditions each year by the 2080s. About 1 billion people live within 25 m (82 ft) of today’s sea level. These areas include many cities on the East Coast of the United States, nearly all of Bangladesh, and 250 million people in China. Relocation of all these people is unimaginable. Low-lying areas will be hardest hit and will be more vulnerable to storms that may become more intense and frequent. The low-lying river deltas of Asia and Africa pose some of the greatest risk, as do small islands near sea level.

HEALTH

Effect of Climate

In some regions of the world, food productivity will improve. However, many areas will see a decrease in agricultural productivity because of the dual impacts of droughts and flooding. As a consequence, malnutrition may become more widespread.

Heat waves, floods, storms, droughts, and fi re are likely to have an impact. Fewer people are likely to die from cold exposure, but the negative health effects are more likely to outweigh the positive ones.

Disease

Waterborne diseases are responsible for 90 percent of the deaths from infectious disease worldwide. They may become more common on a planet that is becoming warmer, more polluted, and more heavily populated. Dengue fever is a viral disease characterized by fever, severe headache, and muscle and joint pain. A more dangerous form of this disease is dengue hemorrhagic fever, which broke out in Paraguay.

Dengue fever now affects 50–100 million people, mostly in tropical and subtropical regions of the world (Science News, March 15, 2005), and is spread by the Aedes aegypti mosquito. Climate change may increase the availability of standing water, which is where this mosquito breeds. With global warming, this mosquito also may migrate north. With warming conditions, there also may be some migration to higher altitudes, whose temperature range will become more conducive to mosquitoes. It is believed that this is occurring in Nairobi, Kenya. The regional distribution of other diseases, such as malaria, which is caused by a parasite spread by the female Anopheles mosquito, similarly may be affected by climate changes.

Displacement of mosquito-carried diseases beyond tropical and subtropical climates exposes a larger population to the disease. This may be offset in part by a better public health infrastructure to combat outbreaks of such diseases in those areas.

Regional Climate Changes

AFRICA

Water is expected to be a problem in Africa. By 2020, many millions of people will be affected by inadequate water supply. This will severely compromise the ability of the African people to grow food. As a result of climate changes, agricultural production throughout Africa may be cut in half by 2020.

ASIA

Throughout the Himalayas, melting glaciers during the next few decades are expected to produce local flooding and rock slides. After that, river flow will decrease, and those who depend on fl owing melt water will see a decline in the availability of that resource. This could affect more than 1 billion people by 2050. Coastal flooding, especially during storms, will become an increasing concern.

Agriculture actually may pick up in the east and southeastern parts of Asia but is expected to fall in the central and southern parts of the continent. Combined with rapid population growth, the risk of hunger in that part of the world may become severe by the middle of the twenty-first century.

AUSTRALIA AND NEW ZEALAND

Decreased precipitation and increased evaporation will increase the risk of drought in this part of the world. The tendency toward increasing concentration of populations near the coast increases the impact of floods and coastal storms. Droughts and wildfires are anticipated in many areas, although some parts of New Zealand many benefit initially from reduced areas prone to frost.

EUROPE

The heat waves and flooding that have ravaged parts of Europe already are expected to continue. Glacial melting will affect water supplies. Short-term benefits may include a reduced demand for heating, increased crop yields, and increased forest growth.

LATIN AMERICA

A significant shift in climate from tropical forest to savannah in the regions east of the Amazon may occur by midcentury. Drier conditions are expected to lead to desertification of some agricultural land. Some crops will no longer be viable, and livestock production may need to be relocated. Some improvements in crop production in temperate regions are possible.

NORTH AMERICA

Decreased snowpack in mountainous areas will contribute to more winter flooding and less flow in summer. There is currently not enough water in the western part of North America for the many intended users, and global warming will make this situation even more difficult. In areas that receive less precipitation, there is an increased risk of brush and forest fires. Farm production may improve by 5–20 percent in some areas where growing seasons are lengthened. Cities may feel a more severe impact from the heat island effect coupled with global warming.

POLAR REGIONS

Melting of ice sheets is expected to lead to a loss of habitat for a number of organisms, including migratory birds, polar animals, and their predators. In the Arctic, the impact on human communities is expected to be mixed. Heating requirements will be reduced, and northern sea routes will become navigable. Traditional ways of life will be threatened, and the indigenous polar populations will be confronted with the need to relocate or adapt to the changing conditions.

SMALL ISLANDS

Erosion of beaches and loss of coral reef in nearby coastal areas will affect people living on small islands throughout the Pacific and Caribbean. Rising sea levels will pose a greater hazard during storms. Less potable water may be available for direct consumption or agriculture.

Back to the Future-Will the Past Repeat Itself?

The geologic history of the earth has been one of alternating warm and cool periods. It may be helpful to look back and understand better what changes have occurred in the past and what insights they may provide for us today. We are currently in a warm phase, but it is not as warm as the extremes of previous interglacial warm periods.

Based on the orbital forces that have driven this cycle, we are very slowly headed for another ice age. According to the IPCC, it is “virtually certain” that natural processes will cause the earth to cool. However, this will not happen for at least 30,000 years. Before that, the earth can be expected to experience a period of global warming caused by the human-enhanced greenhouse effect.

Past warming periods have been accompanied by increases of greenhouse gases such as carbon dioxide and methane. This, however, is seen by climatologists as more an effect rather than a cause of the warming that brought the earth out of past ice ages. Ice-core measurements show that temperatures in Antarctica started to rise centuries before the carbon dioxide levels started to increase. Some observers have cited this as reason to dispute the entire concept of greenhouse gas–induced global warming.

Clearly, the elevated carbon dioxide levels that accompanied the earth’s recovery from past ice ages were not the result of fossil fuel combustion. Some scientists have considered the possibility that elevated carbon dioxide and methane levels came from volcanic activity.

According to the IPCC, it is very unlikely that carbon dioxide triggered the end of the ice ages, but the elevated carbon dioxide did help the earth to warm up. The greenhouse gases amplified the warming effects brought by cyclic changes in the earth’s orbit by providing positive feedback.

The current levels of carbon dioxide and methane in the air today have never been experienced before, leaving the earth in uncharted waters. The levels of the major greenhouse gases-carbon dioxide and methane-are far greater than they have ever been during the past 650,000 years. The rate of increase is also greater than it has ever been at any time during the past 16,000 years.

In the past, when the carbon dioxide and methane levels were at higher levels, the earth was warmer owing to the amplifying effect of the greenhouse gases. Since the last glacial maximum (ice age), the average global temperature likely has increased by 4–7°C (7.2–12.6°F). During that interglacial period, sea levels were about 4–6 m (13–20 feet) higher than they are at present. Greenhouse gas concentration changes in the past occurred much more slowly than at present.

Today, greenhouse gases are changing at a rate that is about 10 times faster. The effect of positive feedback can accelerate the onset of a climate change. When the tongues of glaciers are released into the sea, the movement of the ice mass increases. Surface melting on ice layers increases absorption and results in faster melting. These possibilities lead to concerns about the likelihood of abrupt climate changes. One abrupt change happened about 14,500 years ago. The earth’s climate at the time was in the process of changing from a cold glacial period to a warmer interglacial period when temperatures in North America rapidly returned to near-ice-age conditions. This period is known as the Younger Dryas (named after a flower that grew in cold conditions). The Younger Dryas Period also ended abruptly. Scientists think that this may have been the result of Greenland ice melting, adding freshwater to the North Atlantic. The decrease in salinity may have put a damper on the thermohaline circulation (THC) that drove the Gulf Stream. With less heat being distributed by this massive thermal conveyor belt, the abrupt change may have been triggered. Scientists are asking whether other similar abrupt changes may be initiated by global warming magnified by positive feedbacks.

 

FILM REVIEW: THE DAY AFTER THE DAY AFTER TOMORROW-GOOD LESSONS FROM BAD SCIENCE

The Plot

Jack Hall (Dennis Quaid), a paleoclimatologist, predicts that the earth is about to enter an ice age triggered by global warming. This prediction is fulfilled as a sequence of events triggers abrupt climate change, creating a global super storm and weather disasters. In the span of just a few days, tornados roll through Los Angeles, massive hail falls on Tokyo, and blizzards tear into New York.

The movie: As a result of sea ice melting and a storm surge, the water surrounding the Statue of Liberty is 150–215 ft (45.5–65.5 m) above the present sea level. The science: The maximum amount of potential sea level rise from all ice caps and glaciers melting is 62 m (211 ft). If this melting is the result of greater solar heat retention caused by greenhouse gases, the phase change from ice to liquid water would take many years-not hours, as depicted in the movie.

The movie: Rapid release of freshwater caused an abrupt shutdown of thermohaline circulation, disrupting the Gulf Stream. This instantly plunged the North Atlantic into an ice age.

The science: The IPCC predicts that ice melting from Greenland could slow the thermohaline circulation. However, a complete shutdown is not likely or necessarily a done deal for at least hundreds or thousands of years. Without the Gulf Stream, average temperatures would cool in Europe and North America by perhaps 2.8°C (5°F). “Abrupt” climate change (such as onset of the Younger Dryas Period) has occurred on a time scale of years rather than days, as was depicted in this movie. In the film, thermohaline circulation disruption occurred too rapidly, affected climate too abruptly, and had consequences that were too severe. Otherwise, granting the filmmakers some license for exaggeration, this aspect of the fi lm has some basis in reality, but the portrayal is influenced more by drama than by science.

The movie: The super storm brings cold upper atmospheric air down to the surface, causing severe and rapid freezing.

The science: According to the ideal gas law, descending air would warm up (as its pressure increases) rather than cool. The thinner air in the upper troposphere also would have a small heat capacity and as a result little ability to flash freeze anything in its path.

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