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Climate change

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Global warming is the increase over time of the average temperature of Earth's atmosphere and oceans. In the twentieth century land-based thermometers have recorded such a warming from the 1880s to about 1940, followed by cooling from 1940 to 1975, and another period of warming from 1975 to present. This fluctuation is acknowledged by all scientists although the causes remain controversial -- see 'Historical temperature record' and 'Evidence against a warming period' below.

Scientific opinion

The greenhouse gas theory

The theory that human greenhouse gas emissions are connected with the observed heating of the Earth's atmosphere in the 20th century has steadily gained adherents in the scientific community within the past 15 years, to the extent that many scientific bodies around the world have strongly endorsed it. Even climate researcher Stephen Schneider, who thought in the 1970s that human industrial emissions might lead to global cooling, has become a strong proponent of the global warming hypothesis.

Automobile exhausts, coal-burning power plants, factory smokestacks, and other waste vents of the industrial age now pump six billion tons of carbon dioxide and other greenhouse gases into the earth's atmosphere each year. They are called greenhouse gases because they trap radiant energy from the sun that would otherwise be re-radiated back into space. (The fact that a natural greenhouse effect occurs is well-known and is not at issue in the debate over global warming. Without it, temperatures would drop by approximately 30°C, the oceans would freeze and life as we know it would be impossible.) What climatologists are concerned about, rather, is that increased levels of greenhouse gases in the atmosphere might cause more heat to be trapped. Concentrations of greenhouse gases in the atmosphere are currently at approximately 25% above pre-industrial values. This is considerably higher than at any time during the last 420,000 years, the period for which reliable data exists, from ice cores. From less direct geological evidence it is believed that values this high were last attained 40 million years ago.

The solar variation theory

The climate system varies both through natural, internal processes as well as in response to variations in external forcing from both human and non-human causes, including changes in solar activity and volcanic emissions as well as greenhouse gases. In 1991, Knud Lassen of the Danish Meteorological Institute in Copenhagen and his colleague Eigil Friis-Christensen found a strong correlation between the length of the solar cycle and temperature changes throughout the northern hemisphere. Initially, they used sunspot and temperature measurements from 1861 to 1989, but later found that climate records dating back four centuries supported their findings. This relationship appeared to account for nearly 80 per cent of the measured temperature changes over this period (see graph). Sallie Baliunas, an astronomer at the Harvard-Smithsonian Center for Astrophysics, has been among the supporters of the theory that changes in the sun "can account for major climate changes on Earth for the past 300 years, including part of the recent surge of global warming." [1]

On May 6, 2000, however, New Scientist magazine reported that Lassen and astrophysicist Peter Thejll had updated Lassen's 1991 research and found that while the solar cycle still accounts for about half the temperature rise since 1900, it fails to explain a rise of 0.4 °C since 1980. "The curves diverge after 1980," Thejll said, "and it's a startlingly large deviation. Something else is acting on the climate. ... It has the fingerprints of the greenhouse effect."[2]

Later that same year, Peter Stott and other researchers at the Hadley Centre in the United Kingdom published a paper in which they reported on the most comprehensive model simulations to date of the climate of the 20th century. Their study looked at both natural forcing agents (solar variations and volcanic emissions) as well as anthropogenic forcing (greenhouse gases and sulphate aerosols). Like Lassen and Thejll, they found that the natural factors accounted for gradual warming to about 1960 followed by a return to late 19th-century temperatures, consistent with the gradual change in solar forcing throughout the 20th century and volcanic activity during the past few decades. These factors alone, however, could not account for the warming in recent decades. Similarly, anthropogenic forcing alone was insufficient to explain the 1910-1945 warming, but was necessary to simulate the warming since 1976. Stott's team found that combining all of these factors enabled them to closely simulate global temperature changes throughout the 20th century. They predicted that continued greenhouse gas emissions would cause additional future temperature increases "at a rate similar to that observed in recent decades."[3] A graphical representation of the relationship between natural and anthropogenic factors contributing to climate change appears in "Climate Change 2001: The Scientific Basis," a report by the Intergovernmental Panel on Climate Change (IPCC). [4]

Controversy

Public controversy continues to surround the hypothesis that human activities are contributing to significant global warming. A small number of scientists with backgrounds in climate research -- notably S. Fred Singer, Patrick Michaels, Robert Balling, Sherwood Idso and Richard S. Lindzen -- dispute the theory (see global warming skepticism). Also, a number of industry-backed organizations (including the Global Climate Coalition, the Greening Earth Society and Singer's Science and Environmental Policy Project have claimed that the theory is fraudulent or unproven.

Considerable uncertainty remains about the magnitude of future global warming and its environmental impacts, but the potential impacts are profound. If warming continues at the present rate, it may result in changes in ocean circulation, catastrophic global climate change, loss of biodiversity and irreversible damage to agriculture in those ecoregions most affected. In some regions, e.g. Western Europe, Bangladesh, damage is projected to be extreme, due to loss of Gulf Stream warming and global sea level rise respectively. More frequent bouts of destructive weather are also anticipated, and risk experts in the insurance industry have expressed very strong concerns, advocating a proactive approach based on the precautionary principle. Estimates accepted by the IPCC and by some insurance industry bodies estimate up to 3.5 billion people could be affected by rising disease, loss of fresh water supply, and other impacts.

In opposition stand the fossil fuel industry and its advocates, who have taken a strong stand in opposing most theories of human-caused global warming as well as action to mitigate Global Warming. They argue that crippling the energy industry to prevent an ecological catastrophe does not make "economic sense" - that healthy economies are required to fund technologically innovative "solutions." President G. W. Bush, made this argument in rejecting the Kyoto Protocol. Bush did not reject the science outright, and argued that the greenhouse gas control was a matter of voluntary restraint by industry. Many U.S. states have nonetheless put strong controls on greenhouse gases, rejecting this simple ideology.

This stark standoff between advocates of existing industries have made the scientific questions difficult to distinguish from political ones. While the scientific questions are clear, positions on them and appropriate tests of the theses advanced tend to be hopelessly mired in starting assumptions:

The proportion of scientists who support or oppose any of the various global warming theories is a matter of controversy in its own right. Environmentalists and their allies claim virtually unanimous support for the global warming theory from the scientific community. Opponents maintain that it is the other way around, claiming that the overwhelming majority of scientists either dismiss global warming altogether or merely consider it "unproven" (see global warming skepticism).

The hypothesis that a man-made increase in greenhouse gas concentration would lead to a higher global mean temperature was postulated in the late 19th century by Swedish chemist and 1903 Nobel Laureate Svante Arrhenius (see global warming hypothesis), although, his peers largely rejected that theory.

Some scientists point out that global warming correlates closely with natural factors, especially solar activity. The balance is attributed to the action of humans (see anthropogenic global warming). How much warming is natural or man-made has been hotly debated since the 1990s, by scientists, politicians and advocacy organizations (see global warming controversy).

There is also disagreement on whether the effects of global warming will be beneficial or detrimental. Many researchers predict disastrous consequences for a warming of 1.5 to 7 degrees celsius. The UN's Intergovernmental Panel on Climate Change (IPCC) predicts such a warming is likely within the 21st century, unless severe measures are taken (see Kyoto Protocol.

Other researchers (a small minority), feel that up to 1.5 degrees Centrigade of warming would increase crop yields and stabilize weather; many of these doubt a larger warming is likely. In response, some advocates of strong early measures (well beyond Kyoto) note that the belief in beneficial effects and the doubt that a large warming is possible should be independent if these conclusions were in fact neutrally derived from scientific research, rather than being optimistically driven by ideology or oil money.

Others go somewhat further and indicate that anyone who believes that to 'wait and see', potentially disadvantaging 3.5 billion people to seek narrow advantage in a few growing regions in developed nations, or wait for 'technological fixes', amounts to a declaration of war on the entire planet's population. They argue that long before any northern nation, e.g. Russia, Canada, would enjoy greater crop yields, the developed nations would be exterminated by biological warfare or other weapons of mass destruction launched by groups easily recruited from the most drastically affected world populations. This is of course a political not a scientific argument for action.

To add to the controversy, new findings - within the last 15 years - have indicated that the earth's climate system is inherently unstable, and that global warming could, counterintuitively, precipitate such non-linear, sudden climate shifts as have been discovered to have occurred within the earth's recent past. Ocean circulation, believed to be the key to such climate shifts, has been observed to be slowing, causing alarm among oceanographers. The National Academy Press of the US National Academy of Science issued a report on this phenomenon in 2002, titled Abrupt Climate Change - Inevitable Surprises.[5] "It is important not to be fatalistic about the threats posed by abrupt climate change," it stated. "Societies have faced both gradual and abrupt climate changes for millennia and have learned to adapt through various mechanisms, such as moving indoors, developing irrigation for crops, and migrating away from inhospitable regions. Nevertheless, because climate change will likely continue in the coming decades, denying the likelihood or downplaying the relevance of past abrupt events could be costly."[6]

There is also some disagreement on the historical temperature record. Depending on what direct measurements and proxies are accepted, researchers have presented various scenarios: stable temperature followed by a sudden, steady rise in the 20th century vs. fluctuations of 1 or 2 degrees Centigrade, with near-stable temperature since 1940.

However, the US National Academy of Science, both in its 2002 report to President George W. Bush, and in its latest publications, has strongly endorsed evidence of an average global temperature increase in the 20th century and stated that human activity is heavily implicated in causing this increase.

Advocates of the global warming hypothesis who predict adverse consequences from as little as 1.5 degrees Centigrade of warming nearly all support the Kyoto Protocol as a countermeasure. Some researchers, politicians and businesses oppose it.

Historical temperature record

Climate scientists generally agree that Earth has undergone several cycles of global warming and global cooling in the last 20 thousand years, with the average air temparature fluctuating within a range of about 3 Celsius degrees (5 Fahrenheit degrees), over this time period. During the Medieval Warm Period, for example, Vikings colonized Greenland, but the colonies were abandoned during the Little Ice Age that followed.

Evidence for a current warming period

According to the IPCC, Earth has seen a significant increase in average global surface temperature over the last 150 years.

The main evidence for global warming comes from thermometer measurements from land stations since 1860. The data from these stations, particularly those located outside of the United States, show an average surface temperature increase of 0.4 to 0.8 Celsius degrees during the 20th century. Most of the warming occurred during two periods: 1910 to 1945 and 1976 to 2000. (Source: Intergovernmental Panel on Climate Change, the IPCC).

Secondary evidence comes from observed variations in the snow cover and ice extent, global average sea level, precipitation, cloud cover, El Niño and extreme weather events during the 20th century.

For example, satellite data shows a 10% decrease of snow cover since the late 1960s, and the Northern Hemisphere spring and summer sea-ice extent has decreased by about 10% to 15% since the 1950s and there has been a widespread retreat of mountain glaciers in non-polar regions throughout the 20th century. (Source: IPCC).

Evidence against a current warming period

In January 2002, scientists released data showing that Antarctica had grown about 25% (???). Some editorial writers claimed that this contradicts the expectation that rising temperatures should cause the ice cap to shrink. However, the scientists studying the situation in the Antarctic who released this data point out that local cooling in some areas is consistent with an overall trend of global warming and insist that "the ice-sheet growth that we have documented in our study area has absolutely nothing to do with any recent climate trends."[7]

Weather balloons and satellites measuring the temperature of the atmosphere above the earth's surface show a smaller warming trend than the trend at the earth's surface. Nevertheless, a National Academy of Sciences panel that reviewed this apparent discrepancy concluded that "the warming trend in global-mean surface temperature observations during the past 20 years is undoubtedly real and is substantially greater than the average rate of warming during the twentieth century. The disparity between surface and upper air trends in no way invalidates the conclusion that surface temperature has been rising."[8][9]

Climate models

Climate simulations show that the warming that occurred from 1910 to 1945 can be explained by variation in solar radiation (internal and natural forcing) only (see climate change). The models are used to estimate the relative importance of the various factors mentioned above. Most models show that warming occurring from 1976 to 2000 needs anthropogenic greenhouse gas emissions to be explained.

The IPCC (see below), a United Nations science and public policy organization, published a report saying that scientists believe that anthropogenic greenhouse gases "play an important role in global warming."

This conclusion depends on the accuracy of the models used and on the correct estimation of the external factors. The majority of scientists agree that important climate features are incorrectly accounted for by the climate models but don't think that better models would change the conclusion. (Source: IPCC)

Critics point out that there are flaws in the models and external factors not taken into consideration that could change the conclusion above. Some critics say that the climate simulations are unable to model the cooling effects of the particles, fitting the water vapor feedback, and handling clouds. Critics also point out that the sun may have a share of responsibility for the observed global warming greater than now thought by the majority of the scientific community. Some indirect solar effects may be very important and are not accounted for by the models. So, they argue, the share of global warming caused by anthropogenic greenhouse gases may be lower than thought. (Source: The Skeptical Environmentalist)

Potential Effects

Many public policy organizations and government officials are concerned that the current warming has the potential for harm to the environment and agriculture.

This is a matter of considerable controversy, with environmentalist groups typically emphasizing the possible dangers and groups close to industry questioning the climate models and consequences of global warming - and funding scientists to do so.

Due to potential effects on human health and economy due to the impact on the environment, global warming is the cause of great concern. Some important environmental changes have been observed and linked to global warming.

The examples of secondary evidence cited above (lessened snow cover, rising sea levels, weather changes) are examples of consequences of global warming that may influence not only human activities but also the ecosystems. Increasing global temperature means that ecosystems may change; some species may be forced out of their habitats (possibly to extinction) because of changing conditions, while others may spread. Few of the terrestrial ecoregions on Earth could expect to be unaffected.

Another cause of great concern is sea level rise. Sea levels are rising 1 to 2 centimetres (around half an inch) per decade, and some small countries in the Pacific Ocean are expressing concerns that if this rise in sea level continues, they soon will be entirely under water. Global warming causes the sea level to rise mainly because sea water expands as it warms, but some scientists are concerned that in the future, the polar ice caps and glaciers may melt. As a consequence, the sea level could rise several metres. At the moment, scientists are not expecting any major ice melting in the next 100 years. (Sources: IPCC for the data and the mass media for the general perception that climate change is important.) Some researchers have found a negative correlation between sea level rise and average global temperature; water evaporates more quickly than it expands. (Source: Science and Environmental Policy Project)

As the climate gets hotter, evaporation will increase. This will cause heavier rainfall and more erosion. Many people think that it could result in more extreme weather as global warming progresses.

Global warming can also have other, less obvious effects. The North Atlantic drift, for instance, is driven by temperature changes. It seems as though it is diminishing as the climate grows warmer, and this means that areas like Scandinavia and Britain that are warmed by the drift might face a colder climate in spite of the general global warming. It is now feared that Global Warming may be able to trigger the type of abrupt massive temperature shifts which bracketed the Younger Dryas period.

However, global warming can also have positive effects, since higher temperatures and higher CO2 concentrations improve the ecosystems' productivity. Satellite data shows that the productivity of the Northern Hemisphere has increased since 1982. On the other hand, an increase in the total amount of biomass produced is not necessarily all good, since biodiversity can still decrease even though a small number of species are flourishing. Similarly, from the human economic viewpoint, an increase in total biomass but a decrease in crop harvests would be a net disadvantage. In addition, IPCC models predict that higher CO2 concentrations would only spur growth of flora up to a point; after that, though greenhouse effects and warming would continue there would be no compensatory increase in growth.

The Intergovernmental Panel on Climate Change

Since it is such an important issue, governments need predictions of future trends in global change so they can take political decisions to avoid undesired impacts. Global warming is being studied by the Intergovernmental Panel on Climate Change (IPCC). In its last report, the IPCC made some predictions about future climate change. These predictions are the basis for current political and scientific discussion.

IPCC predictions are based on the same models used to establish the importance of the different factors in global warming. These models need data about anthropogenic emissions of greenhouse gases and aerosols. These data are predicted from economic models based on 35 different scenarios. Scenarios go from pessimistic to optimistic, and predictions of global warming depend on the kind of scenario considered. None of these scenarios consider any kind of measures to avoid global warming.

The models used are primarily based on surface temperature measurements but attempt to predict the temperature of the entire troposphere, not just surface temperatures.

However, a NASA report challenges the success of these models: "The IPCC's 1995 estimate of average global warming at the surface until the year 2100 is +0.18 °C/decade. Climate models suggest that the deep layer measured by the satellite and weather balloons should be warming about 30% faster than the surface (+0.23 °C/decade). None of the satellite or weather balloon estimates are near this value." (Source: NASA Science News 14 August 1998.) Note that "deep layer" refers to the entire troposphere, rather than just the surface.

Nevertheless, proponents of the IPCC assessment say that the current climate models are good in predicting surface temperatures and that this is significant. They furthermore argue that it is surface temperatures that will have the greatest and most direct effect on the environment, agriculture and the stability of polar ice.

The IPCC says that it has corrected the land station data to account for the urban heat island effect. To do: find and summarize their correction technique.

In its last report, IPCC stated that average surface temperature is projected to increase by 1.4 to 5.8 Celsius degrees over the period 1990 to 2100, and the sea level is projected to rise by 0.1 to 0.9 metres over the same period.

IPCC predictions are supposedly the best predictions available but are nevertheless under strong scientific scrutiny. The IPCC concedes that there is a need for better models and better scientific understanding of some climate phenomena, as well as the uncertainties involved. Critics point out that the available data is not sufficient to determine the real importance of greenhouse gases in climate change. Sensitivity of climate to greenhouse gases may be overestimated because of some flaws in the models and because the importance of some external factors may be underestimated.

On the other hand, predictions are based on scenarios, and the IPCC did not assign any probability to the 35 scenarios used. Critics charge that some of the scenarios that predict the largest impacts are not realistic because they contradict "basic economic reasoning".

The Kyoto Protocol

The United Nations Framework Convention on Climate Change (UNFCCC) establishes a process for developing an international response to the perceived global warming problem. 181 countries have ratified the UNFCCC, including all industrial nations. The UNFCCC, however, does not provide any binding emission targets.

The Kyoto Protocol to the UNFCCC proposes binding greenhouse gas limits for developed countries. It has been ratified by 104 countries, representing 43.9% of emissions. Developed countries are required to limit their emissions to, on average, 5.2% below 1990 levels: 29% below pre-Kyoto estimates for 2010. The precise amounts vary from an 8% reduction for the European Union to a permitted increase of 10% for Iceland. Controversially, developing countries, including India and China, are exempted from reductions until they become sufficiently industrialised.

Because global warming is a "tragedy of the commons" problem, the Kyoto Protocol will not take effect until 90 days after countries responsible for over 55% of emissions ratify it. This will occur when Russia ratifies it. The United States, responsible for one-third of emissions of greenhouse, has signed the Kyoto Protocol, but does not intend to ratify it.

References

Every source has a point of view or a sponsor which might be a source of bias. If you discover evidence for bias or a major source of its funding, please include it in the site's description.

Scientific websites:

United Nations websites:

Environmentalist websites:

Industry-sponsored (even in part):

Independent (or receives too little support to constitute "sponsorship"):

Other websites (viewpoint or sponsorship unknown):

See also: Global warming potential, Carbon sequestration, Impact of global climate changes on agriculture

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