11 December 2009

Carbon impacts get major revision

by Kate Melville

The climate may be up to 50 percent more sensitive to atmospheric carbon dioxide in the long term than previously thought and climate projections over the next hundreds of years will likely need to be adjusted to reflect this higher sensitivity, according to a new study in Nature Geoscience.

The research team, led by the University of Bristol and including the U.S. Geological Survey, studied global temperatures 3.3 to 3 million years ago, finding that the averages were significantly higher than expected from the atmospheric carbon dioxide levels at the time.

The U.S. Geological Survey provided the reconstruction of environmental conditions during this timeframe, known as the mid-Pliocene warm period. These data allowed the authors to test the Earth system's sensitivity to atmospheric carbon dioxide.

"Earth is a dynamic system and climate models need to incorporate its multiple feedbacks as well as changes on both fast and long timescales," said the University of Bristol's Dan Lunt, lead author of this article. "This comprehensive outlook allows us to see how sensitive the climate really is to atmospheric carbon dioxide, resulting in more accurate long-term projections."

"This research also emphasizes the importance of examining the past and acquiring real data to understand Earth's climate system," added USGS scientist Harry Dowsett. "Our research on the mid-Pliocene is the most comprehensive global reconstruction for any warm period, and scientists did so by examining fossils to determine sea surface and deepwater ocean temperatures, vegetation, sea ice extent, and other environmental characteristics during that timeframe."

Global average temperatures during the mid-Pliocene were about 3& #176;C greater than today and within the range projected for the 21st century by the Intergovernmental Panel on Climate Change. Therefore, say the researchers, it may be one of the closest analogs in helping to understand Earth's future conditions.

Nature Geoscience
Global warming unstoppable?
Global warming estimates "fundamentally wrong," contends new study
New study shows intimate relationship between ice caps and CO2 levels