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Web Extra Friday, February 2, 2007

Climate report points finger at fossil fuels

Sea ice melting near Greenland presents visible evidence of a changing climate. A new report by the U.N.-sanctioned Intergovernmental Panel on Climate Change states that fossil fuel burning is "very likely" to blame for observed changes in climate, such as decreasing sea ice and rising ocean temperatures. Image is courtesy of Richard Alley.

The world is warming, and the burning of fossil fuels is "very likely" to blame, according to a new report released today in Paris by the Intergovernmental Panel on Climate Change (IPCC). IPCC is a nonpartisan group of thousands of scientists from 180 governments that operates under the auspices of the United Nations Environment Programme and the World Meteorological Organization. The report is "a very emphatic reaffirmation" of the seriousness of human-caused global warming, Richard Somerville of the Scripps Institution of Oceanography said today at a press conference to announce the release of the report.

The IPCC report, the fourth in a series of assessments since the panel was established in 1988 to outline a scientific consensus on current climate change and humans' role in it, is the firmest yet in establishing a link between human activities and global climate change. While the previous 2001 report stated that humans were "likely" the cause of a global warming trend, the new report changes that language to "very likely." The new term is not just semantics, but indicates a quantifiable upgrade in scientific certainty, from 67 percent to "more than 90 percent," said Somerville, who was lead author on the first, overview chapter of the report.

In addition to updated model projections of future climate changes, the new assessment includes observations of currently changing climate, such as rising ocean temperatures, sea ice melting and retreating glaciers — including data from the last six years, which are among the seven warmest years on record. "To me, a highlight of the report is the statement that 'warming of the climate is unequivocal,'" Kevin Trenberth of the National Center for Atmospheric Research (NCAR) and lead author of the report's chapter on observations of climate change in the atmosphere and at Earth's surface, told reporters today.

The observation data are also largely consistent with earlier model projections, and lend confidence to the new report's projections for future climate change, Trenberth said. Globally, the models predict more intense and longer heat waves in summer, shorter winters and more intense hurricanes (see Geotimes, December 2006).

The observational data, as well as more sophisticated modeling techniques, have improved the confidence of scientists in the results of the models, and allowed them to make regional, smaller-scale predictions of climate change over the next century for the first time as well, said Linda Mearns of NCAR, who was lead author on the chapter describing model projections of future climate change. Such changes in the United States include reduced winter length throughout the country, increasing dryness in the Southwest and increasing precipitation in the Northeast, where the additional water vapor is also likely to increase the intensity of both storms and snowfall in that region, she said.

Although sea-level rise is predicted, the report's models do not incorporate some of the most recent, controversial scientific findings, including how melting of the major ice sheets of Greenland and western Antarctica might quickly and dramatically increase sea levels, prompting some scientists to state that the report is ignoring the gorilla in the room. Trenberth denied that the report's writers had overlooked this issue, however, saying that there was simply not yet enough data to accurately quantify the impact of the big ice sheets.

While the new report outlines what scientists currently know about global climate change and includes some projections for the future, two other IPCC working groups are currently completing additional reports on related issues. One, which focuses on the vulnerability and impact of climate change on more specific sectors, such as marine biological systems, coastal regions and human health, will be released in early April, while a third assessment, which looks at strategies for mitigating future climate change, will be released in late April or early May.

Carolyn Gramling

Intergovernmental Panel on Climate Change
"Top climate news stories of 2006," Geotimes, December 2006

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