Amongst some sections of the scientific community, controversy continues to surround the hypothesis that human activities are contributing significantly to global warming. A number of scientists with backgrounds in climate research -- notably Richard S. Lindzen, S. Fred Singer, Patrick Michaels[?], Robert Balling[?] and Sherwood Idso[?] -- dispute the global warming theory (see global warming skepticism). Also, a number of conservative think tanks oppose the theory, some implying that fraud has been involved in advocacy for it (see Science and Environmental Policy Project). Also, some industry-backed organizations (including the Global Climate Coalition, the Greening Earth Society[?] argue that the theory is unproven.
A degree of uncertainty remains. Some believe that the present warming trend shown by some land-based weather stations is likely to continue or increase, fueled by the emission of carbon dioxide and other gases which are believed to be "greenhouse gases". Others argue that solar variability[?] plays a much bigger role in climate change and question whether the human influence is even discernible.
Uncertainty also remains about the likely magnitude of future global warming and its environmental impacts. Environmentalists and other advocates fear that the impacts will be profound. If warming were to continue at the present rate, in adverse 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, but argued that the greenhouse gas control[?] was a matter of voluntary restraint by industry. Although many countries have rejected these arguments and have signed up to the Kyoto Protocol. Also many U.S. states have nonetheless put strong controls on greenhouse gases.
This standoff has made the scientific questions difficult to distinguish from political ones.
The proportion of scientists who support or oppose any of the 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).
Although the arguments over global warming are viewed differently in different parts of the world. In Europe for example the enviromentalist argument over Global warming has gained wider acceptance than in other parts of the world, most notably North America.
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). At the time 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 versus man-made has been debated since the 1990s by scientists, politicians and advocacy organizations.
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 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.
Others suggest that a "wait and see" strategy disadvantages 3.5 billion people in favor of narrow advantage for a few growing regions and developed nations.
New findings have suggested that the earth's climate system is inherently unstable, and that global warming could thus precipitate non-linear sudden climate shifts, as have been discovered to have occurred within the earth's past. Ocean circulation, believed to be the key to such climate shifts, has been observed to be slowing, causing alarm among oceanographers. As briefly mentioned before some scientists fear that the Gulf stream which conveys warm water from the Caribbean Sea across the Atlantic Ocean and is partly responsible for the relative mildness of northern Europe's climate (though other factors also predominate:  (http://184.108.40.206/search?q=cache:OcOF6VQSvzEC:www.ofps.ucar.edu/joss_psg/meetings/clivar-atlantic/Seager.pdf+gulf+stream+responsible&hl=en&ie=UTF-8)). There is a fear that it could be reduced or stopped altogether by the decreased salt content in the sea water, which would result from global warming. Which could cause temperatures in northern europe to drop.
The US National Academy of Science issued a report on this phenomenon in 2002, titled Abrupt Climate Change - Inevitable Surprises. (http://www.nap.edu/books/0309074347/html/) "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."
There is also disagreement on the historical temperature record. Depending on what direct measurements and measurement proxies are used, researchers have presented various derived historical temperature record from stable temperature followed by a sudden, steady rise in the 20th century to non-directed fluctuations of 1 or 2 degrees Centigrade and 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. Others oppose it.
These scientists and statisticians give more weight than the IPCC do to data such as temperature measurements made from weather balloons and satellites that show less warming than land-based stations.