Climate Change

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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 conditions 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.

Earth's climate is changing. In a way, this is nothing new: 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 meters.

But the changes in global climate seen in the last half-century are more drastic than any seen for over a thousand years, and in one way are unique: according to the scientific data, the changes are caused by human activity. Since the Industrial Revolution began in the latter half of the eighteenth century, humans have been digging, pumping, and burning ever-increasing amounts of coal, oil, and natural gas. These fossil fuels contain carbon. When carbon (C) burns, it combines with oxygen (O₂) to form carbon dioxide (CO₂), a clear, odorless gas. 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, 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 (.74°C). Most of the CO₂ increase and most of the warming have happened since 1970, in step with increased burning of fossil fuels.

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 greatly increased the greenhouse effect in a mere century or two, giving Earth's delicately balanced climate machine a sudden, unintentional push. The consequences of that push are only beginning to be seen. Warming, 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 even be reckoned in terms of money.

Scientists have a high certainty 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 in the range that we perceive as visible light. This high-frequency light from the sun 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 out into space at once. Another third is absorbed by the atmosphere and the last third is absorbed by Earth's surface. When light is absorbed by air and land, its energy is converted mostly to heat. Air, water, and land, warmed by the sun, re-radiate or give back this energy as a form of low-frequency light called infrared light or radiation.

Infrared light radiated by Earth's surface or lower atmosphere cannot simply go straight out into space: it has to go through the atmosphere, and in doing so often 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 them.

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. The slower Earth loses energy, the warmer it gets. In sum, 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. 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 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.

Radiative imbalance—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 (a square meter is 1.2 square yards). The watt (W) is the standard unit of power: a 100-watt light bulb dissipates energy at the rate of 100 watts. The standard unit of radiative imbalance, also called radiative forcing, is thus watts per square meter (W/m²). As of 2007, greenhouse gases and tiny airborne particles (aerosols) added to the atmosphere by humans were causing about 1.6 W/m² of radiative forcing.

The amount of energy released directly by burning fuels is too small to have any measurable effect on climate. Climate change is caused by chemicals added to the atmosphere, not by the heat released by power plants, heating systems, automobiles, and other machines.

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' Inter-governmental 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 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.

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.

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

RADIATIVE FORCING: A change in the balance between incoming solar radiation and outgoing infrared radiation. Without any radiative forcing, solar radiation coming to Earth would continue to be approximately equal to the infrared radiation emitted from Earth. The addition of greenhouse gases traps an increased fraction of the infrared radiation, reradiating it back toward the surface and creating a warming influence (i.e., positive radiative forcing because incoming solar radiation will exceed outgoing infrared radiation).

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 three feet (a meter 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 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 a 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 issued 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 to reduce their emissions. In any case, Kyoto did serve as a beginning for international action on climate change, 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 small group of dissident scientists and a large number of climate denialists, that is, persons (rarely having scientific training) who insist that global climate change is a delusion or hoax. Such voices were more drastically 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 spoken; and what it said was that climate change is real, accelerating, dangerous, and human-caused. Importantly, 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. As of the end of 2007, however, the United States and China, the world's 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 experiencing more drastic changes than most other parts of the world. It is warming at twice the global average rate and, by 2007, faster melting of both the floating sea-ice cap over the North Pole and the massive ice sheet on the island of Greenland was occurring 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.

IN CONTEXT: A TIME FOR ACTION

The National Academy of Sciences counsels: “Despite remaining unanswered questions, the scientific understanding of climate change is now sufficiently clear to justify taking steps to reduce the amount of greenhouse gases in the atmosphere. Because carbon dioxide and some other greenhouse gases can remain in the atmosphere for many decades, centuries, or longer, the climate change impacts from concentrations today will likely continue well beyond the 21st century and could potentially accelerate. Failure to implement significant reductions in net greenhouse gas emissions will make the job much harder in the future—both in terms of stabilizing their atmospheric abundances and in terms of experiencing more significant impacts.”

“Governments have proven they can work together successfully to reduce or reverse negative human impacts on nature. A classic example is the successful international effort to phase out of the use of chlorofluorocarbons (CFCs) in aerosol sprays and refrigerants that were destroying the Earth's protective ozone layer. At the present time there is no single solution that can eliminate future warming.”

SOURCE:Staudt, Amanda, Nancy Huddleston, and Sandi Rudenstein. Understanding and Responding to Climate Change. National Academy of Sciences, 2006.

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, by 2050, 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 2008, global CO₂ emissions were accelerating, not slowing, according to the International Energy Agency.

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-to-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

This statement from the Joint Science Academies states their position that global climate change is an important issue that will have severe impacts on the world population.

The declaration acknowledges that global climate change is primarily due to human activity and that it is the responsibility of all countries to address global climate change.

The Joint Science Academies is an association of the heads of the national science academies of the G8+5 countries (Canada, France, Germany, Italy, Japan, Russia, the United Kingdom, and the United States plus Brazil, China, India, Mexico, and South Africa.)

JOINT SCIENCE ACADEMIES' STATEMENT: GLOBAL RESPONSE TO CLIMATE CHANGE

Climate change is real

There will always be uncertainty in understanding a system as complex as the world's climate. However there is now strong evidence that significant global warming is occurring. The evidence comes from direct measurements of rising surface air temperatures and subsurface ocean temperatures and from phenomena such as increases in average global sea levels, retreating glaciers, and changes to many physical and biological systems. It is likely that most of the warming in recent decades can be attributed to human activities. This warming has already led to changes in the Earth's climate.

The existence of greenhouse gases in the atmosphere is vital to life on Earth—in their absence average temperatures would be about 30 centigrade degrees lower than they are today. But human activities are now causing atmospheric concentrations of greenhouse gases—including carbon dioxide, methane, tropospheric ozone, and nitrous oxide—to rise well above pre-industrial levels. Carbon dioxide levels have increased from 280 ppm in 1750 to over 375 ppm today—higher than any previous levels that can be reliably measured (i.e., in the last 420,000 years). Increasing greenhouse gases are causing temperatures to rise; the Earth's surface warmed by approximately 0.6 centigrade degrees over the twentieth century. The Intergovernmental Panel on Climate Change (IPCC) projected that the average global surface temperatures will continue to increase between 1.4 centigrade degrees and 5.8 centigrade degrees above 1990 levels, by 2100.

Reduce the causes of climate change

The scientific understanding of climate change is now sufficiently clear to justify nations taking prompt action. It is vital that all nations identify cost-effective steps that they can take now, to contribute to substantial and long-term reduction in net global greenhouse gas emissions.

Action taken now to reduce significantly the build-up of greenhouse gases in the atmosphere will lessen the magnitude and rate of climate change. As the United Nations Framework Convention on Climate Change (UNFCCC) recognises, a lack of full scientific certainty about some aspects of climate change is not a reason for delaying an immediate response that will, at a reasonable cost, prevent dangerous anthropogenic interference with the climate system.

As nations and economies develop over the next 25 years, world primary energy demand is estimated to increase by almost 60%. Fossil fuels, which are responsible for the majority of carbon dioxide emissions produced by human activities, provide valuable resources for many nations and are projected to provide 85% of this demand. Minimising the amount of this carbon dioxide reaching the atmosphere presents a huge challenge. There are many potentially cost-effective technological options that could contribute to stabilising greenhouse gas concentrations. These are at various stages of research and development. However barriers to their broad deployment still need to be overcome.

Carbon dioxide can remain in the atmosphere for many decades. Even with possible lowered emission rates we will be experiencing the impacts of climate change throughout the 21^st century and beyond. Failure to implement significant reductions in net greenhouse gas emissions now, will make the job much harder in the future.

Prepare for the consequences of climate change

Major parts of the climate system respond slowly to changes in greenhouse gas concentrations. Even if greenhouse gas emissions were stabilised instantly at today's levels, the climate would still continue to change as it adapts to the increased emissions of recent decades. Further changes in climate are therefore unavoidable. Nations must prepare for them.

The projected changes in climate will have both beneficial and adverse effects at the regional level, for example on water sources, agriculture, natural ecosystems and human health. The larger and faster the changes in climate, the more likely it is that adverse effects will dominate. Increasing temperatures are likely to increase the frequency and severity of weather events such as heat waves and heavy rainfall. Increasing temperatures could lead to large-scale effects such as melting of large ice sheets (with major impacts on low-lying regions throughout the world). The IPCC estimates that the combined effects of ice melting and sea water expansion from ocean warming are projected to cause the global mean sea-level to rise between 0.1 and 0.9 metres between 1990 and 2100. In Bangladesh alone, a 0.5 metre sea-level rise would place about 6 million people at risk from flooding.

Developing nations that lack the infrastructure or resources to respond to the impacts of climate change will be particularly affected. It is clear that many of the world's poorest people are likely to suffer the most from climate change. Long-term global efforts to create a more healthy, prosperous and sustainable world may be severely hindered by changes in the climate.

The task of devising and implementing strategies to adapt to the consequences of climate change will require worldwide collaborative inputs from a wide range of experts, including physical and natural scientists, engineers, social scientists, medical scientists, those in the humanities, business leaders and economists.

Conclusion

We urge all nations, in line with the UNFCCC principles, to take prompt action to reduce the causes of climate change, adapt to its impacts and ensure that the issue is included in all relevant national and international strategies. As national science academies, we commit to working with governments to help develop and implement the national and international response to the challenge of climate change.

G8 nations have been responsible for much of the past greenhouse gas emissions. As parties to the UNFCCC, G8 nations are committed to showing leadership in addressing climate change and assisting developing nations to meet the challenges of adaptation and mitigation.

We call on world leaders, including those meeting at the Gleneagles G8 Summit in July 2005, to:

Acknowledge that the threat of climate change is clear and increasing.
Launch an international study to explore scientifically-informed targets for atmospheric greenhouse gas concentrations, and their associated emissions scenarios, that will enable nations to avoid impacts deemed unacceptable.
Identify cost-effective steps that can be taken now to contribute to substantial and long-term reduction in net global greenhouse gas emissions. Recognise that delayed action will increase the risk of adverse environmental effects and will likely incur a greater cost.
Work with developing nations to build a scientific and technological capacity best suited to their circumstances, enabling them to develop innovative solutions to mitigate and adapt to the adverse effects of climate change, while explicitly recognising their legitimate development rights.
Show leadership in developing and deploying clean energy technologies and approaches to energy efficiency, and share this knowledge with all other nations.
Mobilise the science and technology community to enhance research and development efforts, which can better inform climate change decisions.

royal society. “joint science academies' statement: global response to climate change.” june2005. < http://www.royalsociety.org/displaypagedoc.asp?id=20742> (accessed november30, 2007).

BIBLIOGRAPHY

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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.