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Climate Change - The Scientific Consensus
“Warming of the climate system is unequivocal…[and] most of the observed increase in globally averaged temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations.” So said the 600 authors from 40 countries responsible for the Summary for Policymakers  of the United Nations Intergovernmental Panel on Climate Change’s Fourth Assessment Report. Both the National Academy of Science and the British Academy support this conclusion, as do a vast majority of scientists at universities worldwide. Eminent science journals also recognize the scientific consensus regarding global warming and climate change: For example, Oreskes, N., 2004. The Scientific Consensus on Climate Change . Science, v. 306, p.1686 ; Giles, J., 2007. From Words to Action. Nature, v. 445, p578-579.
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Observed Changes
Changes in the Earth’s climate have already been observed. According to the IPCC’s Fourth Assessment Report: Mean global temperature has increased 0.74°C in the past 100 years. Cold days, cold nights and frost events have become less frequent. Hot days, hot nights, and heat waves have become more frequent. Wind intensity has increased. Permafrost coverage, mountain glaciers, and snow cover have declined. In different areas, both drought and heavy precipitation events have increased. Hurricane intensity in the North Atlantic has increased since 1970’s. Global sea level rose by 17 cm during the 20th century, and the rate of sea level rise since 1993 is 3.1 mm per year.
Future Change
A Special Report on Emissions Scenarios (SRES) published in connection with the IPCC’s Third Assessment Report in 2001 represents a possible range of global economic growth and public policies that affect future global greenhouse gas emissions. Climate models fed these different scenarios produce a comparable range of estimates of global warming from 1.1 to 6.4°C and sea level rise from 18 to 59 cm by 2100. Exactly how this climate change will impact human civilization is not known, but the costs associated with extreme weather events, agricultural translocation, and protecting or abandoning coastal areas from sea level rise will be substantial. Furthermore, there is evidence that the rapidity of anthropogenic climate change jeopardizes functional stability of many ecosystems around the world. Ultimately, future climate change and the extent of related environmental disruption are dependent on which of the SRES scenarios most closely resembles the reality of what’s to come.
United States Emissions
According to United States Energy Information Administration, in 2005 (the most recent available data), the U.S. emitted 7,147 million metric tons of greenhouse gases (abbreviated GHGs, expressed as CO2 equivalent), more than any other nation that year and 23% of worldwide emissions. Moreover, despite the scientific consensus of anthropogenic climate change and its dangers, GHG emissions in the United States have increased by about 1% each year since 1990 (EIA report) .
Mitigating Anthropogenic Climate Change – Reducing Greenhouse Gas Emissions
Though China now emits more GHGs than any other nation, the U.S. remains a close second. In light of such large emissions and its role as a world leader in science and technology, the U.S. is well situated to make great reductions in the amount of GHGs that are released globally. However, a long term dependence on fossil fuels has left many policymakers and industry leaders disinclined to change. Instead, naysayers have questioned the scientific evidence for harmful climate change and at the same time decried the costs of reducing GHG emissions as insuperable. Now, science has prevailed over wishful thinkng, and many businesses and organizations, the Climate Conservancy included, are taking steps to mitigate anthropogenic climate change.
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