Los Alamos National Laboratory
To put the current global climate into “paleoclimatic perspective,” it has been about 1,300 years since it was as warm as during the last half century; and one needs to look back some 125,000 years to find a time when the polar ice regions were significantly warmer than they are now.
These estimations are based on studies of indicators such as tree ring width, ancient ice samples, and computer simulations. They’re reported in “Climate Change 2007,” issued by the Intergovernmental Panel on Climate Change (IPCC). The World Meteorological Organization and the United Nations Environment Programme created the panel in 1988.
The IPCC combines the computational findings of the joint National Science Foundation/Department of Energy Community Climate System Model (CCSM) program with data from 17 other groups to create its influential periodic report. The 2007 version is the panel’s fourth, and is divided into three sections. CCSM’s contribution is included in the “Physical Science Basis” section, prepared by Working Group I. The other two sections are “Impacts, Adaptation and Vulnerability” and “Mitigation of Climate Change.”
In its “Summary for Policymakers,” Working Group I writes that carbon dioxide is the most important greenhouse gas created by human activity: “Global atmospheric concentrations of carbon dioxide, methane and nitrous oxide have increased markedly as a result of human activities since 1750 and now far exceed pre-industrial values determined from ice cores spanning many thousands of years. The global increases in carbon dioxide concentration are due primarily to fossil fuel use and land use change, while those of methane and nitrous oxide are primarily due to agriculture.”
The summary adds: “Warming of the climate system is unequivocal, as is now evident from observation in global average and ocean temperatures, widespread melting of snow and ice, and rising global average sea level.”
Even if greenhouse gases held constant at 2000 levels, the report says, global warming would continue for the next two decades due primarily to a lag in the response of the oceans. If greenhouse gas emissions continue at or above current levels, continued warming would “induce many changes in the global climate system during the 21st century that would very likely be larger than those observed during the 20th century.” These changes would likely include more frequent heat waves, some heavy precipitation, and more intense tropical cyclones.
It’s certain the effects of greenhouse gas emissions will be felt far into the future, even if humans immediately stopped adding significant amounts to the atmosphere, but that need not spell doom. The warning signs are more than abundant, yet some scientists feel there is still time to act. How much has yet to be modeled.
« Previous 1 | 2 | 3 | References | Sidebar | Print