Climate projections underestimate CO2 impact

December 10, 2009

The climate may be 30-50 percent more sensitive to atmospheric carbon dioxide in the long term than previously thought, according to a recent study published in Nature Geoscience.

Projections over the next hundreds of years of climate conditions, including , may need to be adjusted to reflect this higher sensitivity.

" is affecting water supplies for cities and farms; leading to more severe droughts, hurricanes, and floods; contributing to more intense ; and putting coastal communities at risk," said Secretary of the Interior Ken Salazar, who is on his way to the global climate change conference convening this week in Copenhagen. "This study and the ongoing work of our USGS scientists will help us continue to build more precise long-term projections and to prepare for the impacts of climate change on our world."

A team of scientists, 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.

These underestimates occurred because the long-term sensitivity of the Earth system was not accurately taken into account. In these earlier periods, Earth had more time to adjust to some of the slower impacts of . For example, as the climate warms and ice sheets melt, Earth will absorb more sunlight and continue to warm in the future since less ice is present to reflect the sun.

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 Dr. Dan Lunt, who is with the University of Bristol and was the lead author of this article. "This comprehensive outlook allows us to see how sensitive the climate really is to , 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," said 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°C (5.5°F) greater than today and within the range projected for the 21st century by the Intergovernmental Panel on Change. Therefore it may be one of the closest analogs in helping to understand Earth's current and future conditions.

More information: To view the article, visit … nt/full/ngeo706.html

Source: United States Geological Survey (news : web)

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3.7 / 5 (6) Dec 11, 2009
What level of confidence is involved in these 'studies'?
All estimates of climate in geological time periods are achieved through the interpretations of 'proxies', i.e. measures of some materials existing now which can be assumed to have been affected by temperature in those geological timeframes.
All such estimates are just that. Estimates.
Clever thinking makes assumptions about the causes of the properties of current materials which are found during these 'studies'.
We have no way of knowing, directly, how accurate such estimates are, and ignorance of just one factor may completely invalidate such 'studies'.
I view all such studies with a jaundiced eye, and rightly so, because as a scientist, I will never be able to take these findings and 'prove' anything.
The strength of the Scientific Method is that all theories arising from observed facts and measurements can have their predictions tested in the crucible of reality.
These findings have no such proof available to them.
5 / 5 (2) Dec 11, 2009
So if CO2 can lag temperatures by as much as several hundred years, did these researchers accurately determine that the increase in temperature followed increasing CO2 levels 3-3.3 million years ago (instead of the other way around), or did they just assume that it happended that way becasue the increase in temp and CO2 happened within the same ballpark period of time and its the accepted AGW mantra that temp follows CO2? Just wondering!

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