Climate Change
Climate Change
Introduction
Climate is the average weather of a region over time. Temperature, winds, heat waves and cold snaps, rainfall, when seasons begin and end, and other weather patterns and events are all aspects of climate. Climates are shaped by a global machinery of ocean currents, winds, forests, ice caps, mountain ranges, bacteria, planetary orbital motions, and many other factors.
Global and regional climates have been changing since Earth formed about 4.5 billion years ago. Ice ages and heat waves have gripped the planet for millions of years on end, sudden warmings and coolings have happened in as little as a decade, ice caps and jungles have spread and shrunk, and seas have risen and fallen by many feet/meters.
However, the changes in global climate seen in the last half-century are more drastic than any seen for at least a thousand years. In one way, these changes are unique in the history of Earth: They are being caused by human beings. Since the Industrial Revolution began in the late 1700s, humans have been digging, pumping, and burning ever-increasing amounts of coal, oil, and natural gas. All these fossil fuels contain carbon. When carbon (C) burns, it combines with oxygen (O2) to form carbon dioxide (CO2), a clear, odorless gas under ordinary Earth surface conditions. In the atmosphere, CO2 acts like an invisible blanket that warms the planet. Not all gases have this warming effect; the main ingredients of Earth’s atmosphere, oxygen (21%) and nitrogen (N) (78%), do not. Those that do have it are called greenhouse gases by analogy to the glass ceilings that keep greenhouses warm inside
As CO2 and the other greenhouse gases—including methane (CH4), nitrous oxide (N2O), and water vapor (H2O)—increase in the atmosphere, Earth’s invisible, gaseous greenhouse roof traps more energy and the planet gets warmer. Since 1750, human activities have increased the atmospheric concentration of CO2 by over a third, to levels not seen on Earth for at least 800,000 years. From 1906 to 2005, Earth’s global average surface-air temperature rose by about 1.3°F (0.74°C). Most of this CO2 increase and warming have happened since 1970, in step with increased burning of fossil fuels worldwide.
Natural influences on climate continue to operate, but they have lately been overwhelmed by human greenhouse emissions from fuel burning, agriculture, deforestation, and other activities. These are now the dominant drivers of climate change.
In large part, the greenhouse effect is natural and necessary. Without it, the oceans would freeze over and most life would die. However, humans have increased the greenhouse effect significantly in a mere century or two, giving Earth’s delicately balanced climate machine a sudden, unintended push. The consequences of that push are only beginning to be seen. Warming, which is the primary or basic effect, triggers a host of other changes: more rain and snow in some places and less in others, more floods and droughts, melting of mountain glaciers and ice caps, rising seas, and extinctions of plants and animals. This is why scientists prefer the phrase “global warming” when speaking of the temperature increase as such and “global climate change” when speaking of global warming plus all the climate changes that warming causes. A few regions, such as parts of Antarctica, may even become cooler or see more snow as the world gets warmer, but such local exceptions do not contradict global warming. There is also the haunting possibility of abrupt, tipping-point climate changes that are difficult to predict but potentially drastic.
In the early twenty-first century, there is global concern about climate change. The well being or survival of hundreds of millions of people may soon be threatened by rising sea levels, disrupted food production, extreme weather, and emergent diseases. Estimates of the costs of climate change over the next century range in the scores of trillions of dollars, while irreversible losses such as species extinctions and lost lives cannot be reckoned in dollar terms.
Scientists are certain that global climate change is happening and are almost certain that it is mostly anthropogenic (caused by humans). Since the 1990s, public debate has turned from the question of whether climate change is real to the question of what can be done to mitigate (lessen) its impact and to prevent further damage to Earth’s environment.
Historical Background and Scientific Foundations
The Greenhouse Effect
The sun is hot, and therefore radiates most of its energy at high frequencies (rates of vibration). About half the sun’s radiation output is in the range that we perceive as visible light. This high-frequency light passes easily through Earth’s atmosphere, which is transparent to it (does not absorb it). Earth reflects about a third of the sunlight it receives back into space at once. Another third is absorbed by the atmosphere, and another third is absorbed by Earth’s surface. When light is absorbed by air, water, and land, its energy is converted mostly to heat. Warmed by the sun, these materials re-radiate or give back this energy as a form of low-frequency light called infrared light or infrared radiation.
Infrared light radiated by Earth’s surface and lower atmosphere cannot simply go straight out into space, it has to go through the upper atmosphere. In attempting to do so, some of it strikes molecules of greenhouse gas, especially water vapor (H2O), CO2, methane (CH4), nitrous oxide (N2O), and artificial chemicals such as chlorofluorocarbons (CFCs). These gases are not transparent to infrared light, but absorb it and are warmed by doing so. This causes the gas molecules themselves to radiate infrared light. Some of this re-radiated infrared light escapes into space, but some shines back down at Earth, warming it, or is absorbed by other greenhouse molecules in the atmosphere, warming the air.
Eventually, almost all the energy Earth receives from the sun will be radiated back out into space, but greenhouse gases slow down this energy loss, and the slower Earth loses energy, the warmer it gets. In short, greenhouse gases warm Earth by slowing the rate at which it loses heat.
Without the greenhouse effect, the average temperature of Earth’s surface-level atmosphere would be about 0°F (-18°C), well below the freezing point of water. The oceans would freeze over and life would thrive only near hot-water vents on the ocean floor.
WORDS TO KNOW
ANTHROPOGENIC: Made by humans or resulting from human activities.
GREENHOUSE GASES: Gases whose accumulation in the atmosphere increase heat retention.
RADIATIVE FORCING: A change in the balance between incoming solar radiation and outgoing infrared radiation, resulting in warming or cooling of Earth’s surface.
Thanks to the natural greenhouse effect, Earth’s average surface temperature is actually 59°F (15°C).
Human beings, by adding billions of tons of CO2 and other gases to the atmosphere, have significantly strengthened Earth’s greenhouse effect in just a couple of centuries. A given amount of greenhouse gas added to the atmosphere causes what climatologists call a radiative imbalance—that is, it causes Earth to radiate, for a while, less energy than it receives from the sun. This adds energy to the land, sea, and air, making them warmer. As Earth warms, its infrared glow eventually brightens to the point where it again loses energy to space as fast as the sun supplies it, but this new balance may not be achieved for thousands of years.
The watt (W) is the standard unit of power. For example, a 100-watt lightbulb dissipates energy at the rate of 100 watts. Radiative imbalance or radiative forcing—the loss or gain over a given area at the top of Earth’s atmosphere of more or less energy than that area receives from the sun—is measured in watts per square meter (W/m2, where a square meter is equal to 1.2 square yards). As of 2008, greenhouse gases and tiny airborne particles (aerosols) added to the atmosphere by humans were causing about 1.6 W/m2 of radiative forcing—adding energy at that average rate to Earth’s climate system over the whole surface of the atmosphere.
The amount of energy released directly by burning fuels is too small to have any measurable effect on climate. Climate change is caused primarily by chemicals released to the atmosphere by power plants, heating systems, automobiles, and other machines, not by the heat released by those devices.
Early Theories of Global Warming
The idea that Earth’s atmosphere might act as a one-way valve for solar energy, letting light in but not letting heat out, was first suggested in the early 1800s. In 1824, French scientist Joseph Fourier (1768–1830) described the greenhouse effect accurately, using the scientific language of his day, when he wrote that “the temperature ‘of Earth’ can be augmented by the interposition of the atmosphere, because heat in the state of light finds less resistance in penetrating the air, than in repassing into the air when converted into non-luminous heat.”
In 1895, Swedish chemist Svante Arrhenius (1859–1927) suggested that changes in atmospheric CO2 concentrations could change Earth’s climate. He estimated that doubling CO2 would increase average global temperature by 9°F (5°C). This was not far wrong, by today’s standards. In 2007, the United Nations’ Intergovernmental Panel on Climate Change (IPCC) said that the result of doubling CO2 would most likely be a 5.4°F (3°C) increase in global temperature. In 1908, Arrhenius was the first to suggest the possibility of an anthropogenic (human-caused) greenhouse effect. Human beings, he suggested, by burning fossil fuels such as coal and so increasing the amount of CO2 in the atmosphere, might warm Earth’s climate. Unable to foretell the huge increase in fossil-fuel use that was about to occur in the twentieth century, Arrhenius suggested that a greenhouse effect might become noticeable in 3,000 years; in fact, it was detectable by the 1990s, less than 100 years later.
In the 1930s, British inventor Guy Stewart Callendar (1898–1964) estimated that doubling CO2 would cause 3.6°F (2°C) of global warming and theorized correctly that warming would be greater in the polar regions. He and some other researchers of that time were, however, mistaken in their belief that anthropogenic global warming was already detectable in the climate record.
The Science Matures: 1950s-1990s
By the mid-1950s, understanding of the physics and chemistry of Earth’s climate system was advancing rapidly and the possibility of anthropogenic climate change was widely discussed among scientists. However, nobody had yet found a way to make the precise measurements of atmospheric greenhouse gases that would show whether humans were actually increasing such gases in the atmosphere: Perhaps, some scientists theorized, the oceans were absorbing CO2 as fast as we were releasing it. But in 1958, American scientist Charles David Keeling (1928–2005) developed sensitive new instruments to measure atmospheric CO2 and installed them on the summit of the Mauna Loa volcano in Hawaii. After just a few years, his data showed a clear result. Although CO2 fell each summer as green plants grew in the Northern Hemisphere (where most of the world’s land is), it rose again in the fall and winter, and it always rose farther than it fell. The result was an upward-tilted zig-zag line. Keeling’s measurements showed that atmospheric CO2 was indeed increasing: a greenhouse effect might, therefore, be occurring.
Keeling’s work was a turning point in climate science, and his chart of rising CO2, now known as the Keeling Curve, has become an icon of global warming. Human activities have raised atmospheric CO2 from about 280 parts per million (ppm) in 1750 to 383 parts per million as of November 2007, a 36.8% increase. (Parts per million refers to the number of molecules in a mixture; for example, 280 parts per million CO2 in air means that of every one million molecules of air, 280 are CO2 molecules.) The Keeling Curve shows that CO2 is still increasing.
Through the 1970s, however, despite the knowledge that atmospheric CO2 was increasing, scientists were still uncertain about whether Earth was about to experience global cooling or global warming. Aerosols—small solid or liquid particles—tended to cool Earth while greenhouse gases tended to warm it, and both are added to the atmosphere by fuel-burning. Perhaps, scientists also speculated, the amount of energy from the sun was changing, or as-yet-unknown natural processes were changing climate. Although a few hasty articles in news magazines proclaimed that we were on the verge of a new ice age, the scientific consensus (the opinion held by the great majority of scientists) was that we did not yet know enough to say what was going to happen to Earth’s climate in the near future.
Meanwhile, the Keeling Curve continued to climb. Surface temperature measurements from thousands of weather stations showed warming trends in most parts of the world, and data from hundreds of tide gauges showed that sea levels were rising worldwide. Layered cylinders of muck from ocean bottoms and of ancient snow layers from deep inside the ice caps of Greenland and Antarctica began to reveal more about paleoclimate (ancient climate), hinting that relatively small changes to radiative forcing, such as slight changes in Earth’s orbit, might trigger large changes in climate. The first mathematical descriptions of the climate machine, called climate models, were developed in the 1960s. Although crude by today’s standards, they predicted several degrees of warming over the next century, a reasonably correct result. Also, starting in the 1970s, satellites began to monitor Earth’s temperature from outer space, supplying a flood of new, independent information about climate.
By the mid-1980s, the doubts of most scientists had been answered—the world was indeed warming. What was more, it would continue to warm, and human beings were the major cause. Scientists warned that global warming would cause a host of other climate changes, many dangerous or costly, from rising seas to shifting rainfall patterns. It became increasingly clear that the question of global warming was more than a matter of abstract curiosity. All human life ultimately depends on farming, and all farming ultimately depends on climate. Also, hundreds of millions of people live within a few feet or so of sea level: rising waters might force their resettlement, if that were possible.
In 1985, a United Nations scientific conference in Austria agreed that significant human-caused global warming was probably about to occur. In 1987, the tenth congress of the U.N.’s World Meteorological Organization recommended ongoing, long-term assessment of climate change by an international group of scientists. The new group, the Intergovernmental Panel on Climate Change (IPCC), was formed in 1988 and given the job of reporting on the scientific community’s understanding of climate so that decision-makers could make informed decisions. The IPCC’s reports, issued every two to five years, have been highly influential in the global discussion of climate change; in 2007, the organization shared the Nobel Peace Prize with former U.S. vice president and climate-change activist Al Gore (1948–). The first IPCC Assessment Report was issued in 1990 and the fourth in 2007. A fifth report is due around 2012.
The IPCC’s 1990 report advised that global warming was probably happening and might cause many problems. Mildly alarmed—there were still many doubts and uncertainties—almost all the world’s nations sent representatives to a climate summit in Rio de Janeiro, Brazil, in 1992. There, a treaty addressing the problem of global climate change was negotiated. This treaty, the United Nations Framework Convention on Climate Change (UNFCCC), did not place binding obligations on any countries but did acknowledge the reality of anthropogenic global climate change. Under the UNFCCC, industrialized countries made a non-binding commitment to reduce their greenhouse-gas emissions and to help developing (poorer) countries reduce theirs as well.
Throughout the 1990s, despite efforts by a few scientists and many political commentators to cast doubt
on the reality, dangerousness, or human-caused nature of climate change, a scientific consensus on climate change emerged. Computerized climate models became more complex and realistic every year, the Keeling Curve continued to climb (as well as similar records charting increases in other greenhouse gases), global average temperature continued to rise, and paleoclimate studies showed that, thanks to human activity, there was more CO2 in the air than there had been for at least 600,000 years. Later, data from Antarctic ice cores pushed this back to 800,000 years. Earth, climatologists confirmed, was probably warmer by the late 1990s than it had been for at least 1,100 years, maybe much longer.
The countries that had signed the UNFCCC in 1992, including the world’s then-largest greenhouse polluter, the United States, held regular meetings in the following years to discuss the changing science of climate change and to plan counter-action. These meetings resulted in a protocol or add-on to the UNFCCC, the Kyoto Protocol of 1997. The Kyoto Protocol was rejected by U.S. leaders and those of a few other countries—Australia did not sign the protocol until December 2007—but it was affirmed by all other signatories of the UNFCCC. Under Kyoto, industrialized countries made binding promises to reduce their own greenhouse emissions and to help developing countries do the same.
Kyoto was controversial. The United States refused to commit to the protocol because it did not require rapidly developing nations, such as China and India, to reduce their emissions. In any case, Kyoto did serve as a beginning for international action on climate change,
IN CONTEXT: CLIMATE CHANGE IS REAL AND DRIVEN BY HUMAN ACTIVITY
“Most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse-gas concentrations. This is an advance since the TAR’s [Third Assessment Report] conclusion that ‘most of the observed warming over the last 50 years is likely to have been due to the increase in greenhouse-gas concentrations.' Discernible human influences now extend to other aspects of climate, including ocean warming, continental-average temperatures, temperature extremes and wind patterns.”
SOURCE: Solomon, S., et al, eds. “IPCC, 2007: Summary for Policymakers.” In: 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.
establishing mechanisms for carbon emissions trading and formalizing the commitment of most industrial nations to reduce their emissions. Kyoto was not meant to be the final word on climate action; signers agreed from the beginning to replace Kyoto with an updated agreement starting in 2012.
In 2001 and in 2007, the IPCC released its third and fourth Assessment Reports on climate change. The 2007 report, prepared by over 2,500 scientists and economists appointed by scores of governments, declared that global warming was “unequivocal” (certain) and that there was at least a 90% probability that human beings were the cause. The report had an unprecedented impact on world opinion on climate change, creating a heightened sense of urgency. It also appeared to have greatly reduced the U.S. news media’s longstanding practice of false balance, that is, framing stories as if there were a balanced climate “debate” between two more-or-less equally authoritative groups of scientists, one alleging the reality of climate change and the other denying it.
After the 2007 IPCC report, it was clear that such a balanced debate did not exist, despite the continued existence of a relatively small number of dissident scientists and a large number of climate denialists, that is, persons (few of whom have scientific training) who insist that global climate change is a delusion or even a delib-rate hoax. Such voices were more marginalized than ever after 2007, when the world climate-science community came as close to speaking with a single voice as any scientific community had ever done, announcing that climate change is in fact real, accelerating, dangerous, and human-caused. Also important, it also said that climate change could be mitigated (made less severe) at a fairly low cost if prompt action were taken to reduce greenhouse emissions. At the end of 2007, however, the United States and China, the world’s two largest greenhouse polluters, both remained unfriendly to the idea of binding emissions limits, making the future of efforts to control global climate change uncertain.
Impacts and Issues
Global climate change is global but not uniform. That is, it affects different regions differently. For example, the region at and around the North Pole, the Arctic, is warming at about twice the global average rate. By 2007, both the floating sea-ice cap over the North Pole and the massive ice sheet on the island of Greenland were melting faster than scientists had predicted as recently as 2001. In the summer of 2007, the floating north-polar ice cap shrank to the smallest size ever observed, opening up a clear-water channel around the northern edge of North America from the Pacific to the Atlantic—the fabled Northwest Passage—for the first time in recorded history. Arctic permafrost (permanently frozen soil) has been melting over larger areas, an event that may soon release large quantities of the greenhouse gas methane, which would cause still more rapid global warming.
Water from the melting of mountain glaciers, Greenland’s ice cap, and ice on the West Antarctic Peninsula runs downhill to the sea, increasing the amount of water in the oceans. Global warming also heats up the topmost layer of the ocean, causing it to expand. The combined effects of thermal expansion and added water have caused sea levels to rise about 6 in (15 cm) since 1900, with sea level rising more quickly in the last few decades. The habitability of low-lying coastal cities, where hundreds of millions of people live, is threatened by rising oceans. Many small islands in the Pacific, the Indian Ocean, the Bahamas, and elsewhere may be rendered completely uninhabitable by rising seas. Even if greenhouse-gas emissions leveled off in the near future, sea-level rise and other climate changes will probably continue for centuries, though more slowly and to less extreme conclusions, because it will take that long for Earth’s massive oceans to get into balance with the radiative forcing from greenhouse gases already added to the atmosphere.
Most types of extreme weather are predicted to become more common with global climate change. Extreme weather includes heat waves, downpours, droughts, and powerful storms. The only form of extreme weather likely to become less common is cold waves. In August 2007, the World Meteorological Organization announced that during the first half of 2007, Earth showed significant increases above long-term global averages in the frequency of extreme weather events, including heavy rainfalls, tropical cyclones, heat waves, and wind storms. Global average temperatures for January and April of 2007 were the highest recorded for those two months since records began in the 1800s.
In some areas, such as the western United States, water shortages may eventually become severe and chronic, interfering with agriculture. Increased flooding and drought may interfere with agriculture in other parts of the world, such as Asia and Africa. Deterioration of coral reefs and other changes to the seas, including acidification from high CO2 in the atmosphere dissolving in the oceans, may cause fisheries to decline. Fisheries presently provide 2.6 billion people with 20% or more of their dietary protein. Wind patterns, ranges inhabited by plants and animals, and rainfall patterns are also projected to change. Hurricanes may grow more frequent and severe, destroying property along coasts.
All continents will see effects of climate change, but so far the continental United States and most of Europe have seen less drastic effects than many other regions and are likely to continue to do so. The IPCC has predicted that the most severe effects of climate change will afflict the world’s poorest countries, which are mostly in the tropics. Not only do these countries happen to be located where they will be more severely affected by climate change, but they have fewer resources—less money, less technological flexibility—to help them adapt to climate change. Many people will likely be driven from their homes in poorer countries by stresses associated with climate change. In 2005, the United Nations University Institute for Environment and Human Security estimated that the number of environmental refugees might rise to 150 million by 2050, mostly as a result of climate change.
Animals and plants will also be endangered by changing climate. In 2004, scientists calculated that, out of a random sample, 1,103 animal and plant species, 15-37% would be committed to extinction as a result of climate change. Extinction is the death of all members of a species, the irreversible death of the species itself. The scientists estimated that in many if not most ecological regions, climate change will become the greatest threat to biodiversity—the most likely cause of most extinctions—by 2050.
Efforts to mitigate climate change by reducing greenhouse-gas emissions are being made, such as the Kyoto Protocol, but so far these efforts have not reached a level where they are likely to greatly affect the future course of climate change. Some nations have decreased their emissions over the last decade, but others, notably China and India, have greatly increased theirs along with increasing economic activity, including increased manufacturing for export to Western markets. As of 2007, according to the International Energy Agency, global CO2 emissions were accelerating, not slowing.
Choices by individual persons that reduce greenhouse emissions can do much to reduce global climate change. Such choices include the more efficient use of
energy and materials in all departments of life. Purchase of carefully chosen carbon offsets may also be helpful. However, greatly reducing greenhouse-gas emissions will require the restructuring of the world’s present energy economy, which has been founded on cheap fossil fuels for two centuries. Only a new energy economy, one founded on efficiency, thrift, and non-emitting or low-emitting energy technologies, can produce the 50-90% reductions in emissions that some scientists argue must occur by about 2050 to lessen the chance that Earth will experience uncontrolled greenhouse warming and climate change. However, it is unlikely that such a global change will happen in time without global cooperation to reduce greenhouse emissions by all the world’s major governments, perhaps acting on an improved Kyoto model.
Primary Source Connection
In November 2000, the National Assessment Synthesis team submitted its first two reports to Congress: a National Assessment Overview and a National Assessment Foundation Report. The 154-page overview summarized the collective research and analysis of environmental scientists and policy makers regarding the effects and impacts of climate change on the United States. An excerpt of the report summarizing the National Assessment Synthesis Team’s major conclusions regarding climate change in the United States follows.
The longer National Assessment Foundation Report, comprising more than six hundred pages, includes the scientific information and research used to draw conclusions and to develop the trends described in the overview. Much of the work included in the overview and the foundation report is the result of extensive workshops with scientists, policy makers, and the general public throughout the United States. The project divided the issues associated with climate change into five sectors: agriculture, forests, water, human health, and coastal and marine resources. Further, twenty different regions within the United States were identified for assessment.
CLIMATE CHANGE IMPACTS ON THE UNITED STATES: THE POTENTIAL CONSEQUENCES OF CLIMATE VARIABILITY AND CHANGE
Long-term observations confirm that our climate is now changing at a rapid rate. Over the 20th century, the average annual US temperature has risen by almost 1°F (0.6°C) and precipitation has increased nationally by 5 to 10%, mostly due to increases in heavy downpours. These trends are most apparent over the past few decades. The science indicates that the warming in the 21st century will be significantly larger than in the 20th century. Scenarios examined in this Assessment, which assume no major interventions to reduce continued growth of world greenhouse-gas emissions, indicate that temperatures in the US will rise by about 5-9°F (3-5°C) on average in the next 100 years, which is more than the projected global increase. This rise is very likely to be associated with more extreme precipitation and faster evaporation of water, leading to greater frequency of both very wet and very dry conditions.
This Assessment reveals a number of national-level impacts of climate variability and change including impacts to natural ecosystems and water resources. Natural ecosystems appear to be the most vulnerable to the harmful effects of climate change, as there is often little that can be done to help them adapt to the projected speed and amount of change. Some ecosystems that are already constrained by climate, such as alpine meadows in the Rocky Mountains, are likely to face extreme stress, and disappear entirely in some places. It is likely that other more widespread ecosystems will also be vulnerable to climate change. One of the climate scenarios used in this Assessment suggests the potential for the forests of the Southeast to break up into a mosaic of forests, savannas, and grasslands. Climate scenarios suggest likely changes in the species composition of the Northeast forests, including the loss of sugar maples. Major alterations to natural ecosystems due to climate change could possibly have negative consequences for our economy, which depends in part on the sustained bounty of our nation’s lands, waters, and native plant and animal communities.
A unique contribution of this first US Assessment is that it combines national-scale analysis with an examination of the potential impacts of climate change on different regions of the US. For example, sea-level rise will very likely cause further loss of coastal wetlands (ecosystems that provide vital nurseries and habitats for many fish species) and put coastal communities at greater risk of storm surges, especially in the Southeast. Reduction in snowpack will very likely alter the timing and amount of water supplies, potentially exacerbating water shortages and conflicts, particularly throughout the western US. The melting of glaciers in the high-elevation West and in Alaska represents the loss or diminishment of unique national treasures of the American landscape. Large increases in the heat index (which combines temperature and humidity) and increases in the frequency of heat waves are very likely.
These changes will, at minimum, increase discomfort, particularly in cities. It is very probable that continued thawing of permafrost and melting of sea ice in Alaska will further damage forests, buildings, roads, and coastlines, and harm subsistence livelihoods. In various parts of the nation, cold-weather recreation such as skiing will very likely be reduced, and air conditioning usage will very likely increase.
Highly managed ecosystems appear more robust, and some potential benefits have been identified. Crop and forest productivity is likely to increase in some areas for the next few decades due to increased carbon dioxide in the atmosphere and an extended growing season. It is possible that some US food exports could increase, depending on impacts in other food-growing regions around the world. It is also possible that a rise in crop production in fertile areas could cause prices to fall, benefiting consumers. Other benefits that are possible include extended seasons for construction and warm weather recreation, reduced heating requirements, and reduced cold-weather mortality.
Climate variability and change will interact with other environmental stresses and socioeconomic changes. Air and water pollution, habitat fragmentation, wetland loss, coastal erosion, and reductions in fisheries are likely to be compounded by climate-related stresses. An aging populace nationally, and rapidly growing populations in cities, coastal areas, and across the South and West are social factors that interact with and alter sensitivity to climate variability and change.
There are also very likely to be unanticipated impacts of climate change during the next century. Such “surprises” may stem from unforeseen changes in the physical climate system, such as major alterations in ocean circulation, cloud distribution, or storms; and unpredicted biological consequences of these physical climate changes, such as massive dislocations of species or pest outbreaks. In addition, unexpected social or economic change, including major shifts in wealth, technology, or political priorities, could affect our ability to respond to climate change.
Greenhouse-gas emissions lower than those assumed in this Assessment would result in reduced impacts. The signatory nations of the Framework Convention on Climate Change are negotiating the path they will ultimately take. Even with such reductions, however, the planet and the nation are certain to experience more than a century of climate change, due to the long lifetimes of greenhouse gases already in the atmosphere and the momentum of the climate system. Adapting to a changed climate is consequently a necessary component of our response strategy.
Adaptation measures can, in many cases, reduce the magnitude of harmful impacts, or take advantage of beneficial impacts. For example, in agriculture, many farmers will probably be able to alter cropping and management practices. Roads, bridges, buildings, and other long-lived infrastructure can be designed taking projected climate change into account. Adaptations, however, can involve trade-offs, and do involve costs. For example, the benefits of building sea walls to prevent sea-level rise from disrupting human coastal communities will need to be weighed against the economic and ecological costs of seawall construction. The ecological costs could be high as seawalls prevent the inland shifting of coastal wetlands in response to sea-level rise, resulting in the loss of vital fish and bird habitat and other wetland functions, such as protecting shorelines from damage due to storm surges. Protecting against any increased risk of water-borne and insect-borne diseases will require diligent maintenance of our public health system. Many adaptations, notably those that seek to reduce other environmental stresses such as pollution and habitat fragmentation, will have beneficial effects beyond those related to climate change.
Vulnerability in the US is linked to the fates of other nations, and we cannot evaluate national consequences due to climate variability and change without also considering the consequences of changes elsewhere in the world. The US is linked to other nations in many ways, and both our vulnerabilities and our potential responses will likely depend in part on impacts and responses in other nations. For example, conflicts or mass migrations resulting from resource limits, health, and environmental stresses in more vulnerable nations could possibly pose challenges for global security and US policy. Effects of climate variability and change on US agriculture will depend critically on changes in agricultural productivity elsewhere, which can shift international patterns of food supply and demand. Climate-induced changes in water resources available for power generation, transportation, cities, and agriculture are likely to raise potentially delicate diplomatic issues with both Canada and Mexico.
This Assessment has identified many remaining uncertainties that limit our ability to fully understand the spectrum of potential consequences of climate change for our nation. To address these uncertainties, additional research is needed to improve understanding of ecological and social processes that are sensitive to climate, application of climate scenarios and reconstructions of past climates to impacts studies, and assessment strategies and methods. Results from these research efforts will inform future assessments that will continue the process of building our understanding of humanity’s impacts on climate, and climate’s impacts on us.
National Assessment Synthesis Team
NATIONAL ASSESSMENT SYNTHESIS TEAM. “CLIMATE CHANGE IMPACTS ON THE UNITED STATES: THE POTENTIAL CONSEQUENCES OF CLIMATE VARIABILITY AND CHANGE.” U.S. GLOBAL CHANGE RESEARCH PROGRAM. JUNE 12, 2000.
Primary Source Connection
The following news article asks the question of whether or not the United Nations-sponsored Intergovernmental Panel on Climate Change (IPCC) report on climate warming is politically biased. The report claims that global warming is a crisis provoked by humans. Some IPCC contributors who are skeptical of the human role in causing global warming claim their input was not included in the report, while others claim that because thousands of scientists cannot agree on everything, the general consensus is reported.
CLIMATE WARMING SKEPTICS: IS THE RESEARCH TOO POLITICAL?
In May, based on the work of hundreds of scientists from around the world, the United Nations issued a groundbreaking report on Earth’s climate. Its findings were sobering:
Most of the increase in temperatures seen in the last 50 years, it said, is very likely—with more than 90 percent certainty—to be due to greenhouse gases produced by human activities.
The report, with two others this year from the UN-sponsored Intergovernmental Panel on Climate Change (IPCC) are considered to be the definitive distillations of humankind’s understanding of human-driven climate change.
“The IPCC reflects the consensus of the vast majority of scientists in the field, and you can assess this by looking at the journals, the meetings, the conference proceedings, etc.” says Gavin Schmidt, a climate scientist at the National Aeronautics and Space Administration’s Goddard Institute for Space Studies, in an e-mail.
Yet a small but vocal minority continues to question the reports’ conclusions. Because the IPCC is an organ of the United Nations, they say, the reports are politically skewed.
“We hear over and over the assertion that there is a consensus that ‘global warming’ is man-made and a crisis. Says who?” writes Joseph Bast, president of The Heartland Institute, a nonprofit dedicated to discovering “free-market solutions to social and economic problems,” on its web site.
Others say the authors are biased; dissent is quashed during the report’s drafting, they charge. “Some of my comments and reviews were sort of rejected,” says John Christy, a state climatologist at the University of Alabama at Huntsville and an IPCC contributing author who has doubts about humans’ role in the observed warming. “I’m sure that [I] wasn’t the only one.”
The most vehement argue that evidence proving that human activity is causing global warming simply doesn’t exist. “We’ve had a Greenhouse Theory with no evidence to support it—except a moderate warming turned into a scare by computer models,” says S. Fred Singer, a professor emeritus of environmental science at the University of Virginia and vocal climate skeptic, in the press release for a study titled “Challenge to Scientific Consensus on Global Warming,” published by the Hudson Institute.
In reply, IPCC authors point to what they characterize as the lengthy, exhaustive, and transparent process behind the reports.
‘We can’t ignore anything’
“The thing about the IPCC report which is not adequately appreciated by many is how rigorous and comprehensive the overall process is,” says Kevin Trenberth, head of the National Center for Atmospheric Research’s climate analysis section and a coordinating lead author on one chapter of the IPCC report. “We have to weigh all the evidence, but we can’t ignore anything.”
The IPCC itself does not conduct research but calls on a diverse group of scientists from around the world to review existing research. For example, Dr. Trenberth’s group, Working Group I, had 152 lead authors. Some 25 percent were within a decade of having received their PhDs; 75 percent had not been a lead author on any previous IPCC report. And 35 percent hail from non-Firs World nations. The authors were nominated for participation by their own governments.
The scientist-authors pen a first draft of their findings, which is then sent to other experts in the field for review. Another draft is generated that receives comments from anyone who requests a copy. Review editors who operate independently of the authors ensure that every comment is logged and, if deemed relevant, responded to.
Yet another draft is generated and more reviewers, including governments, weigh in. Each country then solicits reviews nationally. In the United States, the government posted the draft on a web site and invited comments from the public.
Some comments couldn’t be included because they referred to research published too late to include, says Richard Somerville, a coordinating lead author in Working Group I, in an e-mail. “And we got a certain amount of pure nonsense. But if we rejected a comment, our reasons are written down and [are] public.”
Working Group I received some 30,000 direct comments.
Conspiracy unlikely among so many
“If there was going to be a conspiracy among scientists, I can’t imagine how you’d manage it,” says Martin Manning, director of the IPCC Working Group I Support Unit. “Conspiracy theories run into credibility problems if you start to explore how it would work and how you’d have to make it happen.”
Even so-called climate skeptics recognize the report’s comprehensiveness. “Nobody could ever imagine 2,500 scientists ever agreeing on everything,” says Dr. Christy. He calls the report “a good distillation.”
Dr. Singer, also a skeptic, calls the full report “a very useful document.” He reserves his stronger criticism for the Summary for Policymakers, a document all government delegations must unanimously approve.
“The summary is basically a political document,” Singer argues. He points to wrangling over the Working Group I summary. China asked that the word “very” be removed from the text stating that observed warming was “very likely” due to human-emitted greenhouse gases.
In fact, the authors refused to change the wording. (A write-up of the Paris meeting is available at www.iisd.ca/climate/ipwgl/.) The authors and other delegates reminded China that their task was to draft a summary “for” not “by” policymakers. “The scientists determine what is said, but the governments determine how it’s said,” Trenberth says. “What we have to do is make sure it’s consistent with the science.”
As for a worldwide conspiracy, IPCC’s Dr. Manning asks why 113 nations would endorse a fiction that’s beneficial to none. He says he’s never met a senior politician who is eager to deal with climate change. “A lot of politicians would breathe a huge sigh of relief if someone could actually say, ‘No, we’ve got it wrong,’” he says.
Dissenting studies were weighed
But is dissent being quashed? Where the literature indicates a range of possibilities—the role of aerosols in climate change, for example—the full report discusses these issues at length. Even studies included in the just-released “Documented Doubts of Man-Made Global Warming Scares,” a list by the Hudson Institute purporting to cast doubt on the consensus on human-driven cli
“Those studies are taken into account,” Trenberth says. “Every one of them.”
The reason for the dearth of dissenting views may be quite mundane. According to one science historian, in the peer-reviewed scientific literature—the backbone of science and the source material for the IPCC report— hardly a dissenting voice is heard.
Naomi Oreskes, a professor of history at the University of California, San Diego, and an adjunct professor of geosciences at Scripps Institution of Oceanography there, searched for the keywords “global climate change” in a large database, a compilation of scientific journals. Of the 928 papers she found, not one questioned whether global warming was human-induced or if it was real. (The studies she found are a large representative sample, Dr. Oreskes says. She puts the total number of papers on global climate change at about 11,000.) “The basic reality of anthropogenic global climate change is no longer a subject of scientific debate,” she concludes.
Her study implies that since the IPCC must draw from scientific literature, it didn’t find many papers that argued against human-driven change. Contrarian studies didn’t make it through science’s portal to respectability: scientific journals.
Maybe the scientific community does have it wrong about climate change, Oreskes says. After all, the majority has been incorrect before. But in this case, the contrarians are not, as they often paint themselves, on science’s vanguard, she says. The discussion of global warming among scientists is not new—it’s been going on for half a century, Oreskes says. The skeptics have had their day in court, she says: “It’s just that nobody agrees with them.”
What is the IPCC?
Founded in 1988 by the United Nations, the Intergovernmental Panel on Climate Change (IPCC) is charged with, among other things, identifying gaps in knowledge about climate change science and assessing the potential impacts of greenhouse gases. The IPCC has released four reports—in 1990, 1995, 2001, and 2007.
The IPCC does not conduct research. Instead, it enlists a diverse group of scientists from around the globe to review existing research. Governments nominate their own scientists for participation on the panel, and the result is a mix of contributors from all over the world. Some 600 authors took three years to draft the May IPCC report on “Climate Change 2007: the Physical Science Basis.” More than 620 expert reviewers commented on its various drafts, and 113 countries approved it.
The IPCC has three working groups, each with a different area of focus. Each is charged with releasing its own report. In 2007 Working Group I focused on the physical science of climate change; Working Group II on impacts, adaptation, and vulnerability; and Working Group III on how to stop or slow down climate change (mitigation).
The IPCC will release a summarized report of all three working groups in November.
Each Working Group report has a summary for policymakers (SPM) that contains the key findings from the main report. Before its release, government delegations review the SPM line by line. All participating governments must approve the SPM unanimously. If a delegation absolutely disagrees with something in the report, then the line in question is excised. But governments cannot alter the text to better align with their own interests.
“We the scientists… never lost control of the report,” says Richard Somerville, a coordinating lead author for Working Group I, in an e-mail. “Governments wordsmithed it usefully… but the science wasn’t distorted or watered down in any manner. The SPM is a Summary FOR Policymakers, not BY Policymakers.”
Moises Velasquez-Manoff
VELASQUEZ-MANOFF, MOISES. “CLIMATE WARMING SKEPTICS: IS THE RESEARCH TOO POLITICAL?” CHRISTIAN SCIENCE MONITOR OCTOBER 4, 2007.
See Also Carbon Dioxide (CO2); Carbon Dioxide (CO2) Emissions; Carbon Sequestration; Global Warming; Greenhouse Effect; Greenhouse Gases; Intergovernmental Panel on Climate Change; IPCC 2007 Report
BIBLIOGRAPHY
Books
Gore, Al. An Inconvenient Truth: The Planetary Emergency of Global Warming and What We Can Do About It. Emmaus, PA: Rodale Press, 2006.
McCaffrey, Paul. Global Climate Change. Minneapolis, MN: H. W. Wilson, 2006.
Metz, B., et al, eds. Climate Change 2007: Mitigation of Climate Change: Contribution of Working Group III to the Fourth Assessment Report of the
Intergovernmental Panel on Climate Change. New York: Cambridge University Press, 2007.
Parry, M. L., et al, eds. Climate Change 2007: Impacts, Adaptation and Vulnerability: Contribution of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. New York: Cambridge University Press, 2007.
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.
Weart, Spencer. The Discovery of Global Warming. Cambridge, MA: Harvard University Press, 2004.
Periodicals
Alley, Richard B. “Abrupt Climate Change.” Scientific American (November 2004).
Collins, William, et al. “The Physical Science Behind Climate Change.” Scientific American (August 2007).
Oreskes, Naomi. “The Scientific Consensus on Climate Change.” Science 306 (2004): 1686.
Thomas, Chris D. “Extinction Risk from Climate Change.” Nature 427 (2004): 145-148
Thomas, Karl, and Kevin Trenberth. “Modern Global Climate Change.” Science 302 (2003): 1719–1723.
Web Sites
United Nations. “United Nations Framework Convention on Climate Change.” 2008. http://unfccc.int/2860.php (accessed March 19, 2008).
United Nations. “Intergovernmental Panel on Climate Change.” 2008. http://www.ipcc.ch (accessed March 19, 2008).
U.S. Environmental Protection Agency. “Climate Change.” November 19, 2007. http://epa.gov/climatechange/index.html (accessed March 18, 2008).
Larry Gilman