Sensitive side

May 05, 2010 By Rosemary Sullivant
The carbon dioxide molecule. New research suggests that the Earth is more sensitive to carbon dioxide in the air than we thought.

(PhysOrg.com) -- A little extra carbon dioxide in the air may, unfortunately, go further towards warming Earth than previously thought. A team of British and U.S. researchers have uncovered evidence [1] that Earth’s climate may be up to 50 percent more sensitive to long-term increases in atmospheric carbon dioxide than current climate models predict. The reason for the underestimation, they say, may be due to long-term changes in ice sheets and vegetation that are not well represented in today’s global climate models.

Just how much will global temperature rise in response to increases in atmospheric ? This is one of the key questions that climate scientists need to answer. According to the climate models used in the most recent report from the Intergovernmental Panel on Climate Change (IPCC), doubling the amount of carbon dioxide in the atmosphere from pre-industrial levels is expected to warm Earth by about 3 degrees Celsius (5 degrees Fahrenheit), once the atmosphere and oceans spend a few years or decades adjusting and reaching a balance.

But according to a recent study by a team of researchers that includes Gavin Schmidt of NASA’s Goddard Institute for Space Studies, Earth’s climate is also influenced by other, much slower processes. These include changes in ice sheets, vegetation and , for example, that take place over hundreds and thousands of years. Because of their complexity and long timescales, these processes are almost impossible to integrate into today’s climate computer models. As a result, it has been difficult to know just what their effect on Earth’s climate sensitivity would be.

To learn more about this sensitivity, Schmidt and his co-authors looked back 3 million years into Earth’s past. They used a that describes the oceans and atmosphere to predict, retroactively, the climate of the mid-Pliocene — a period when both and atmospheric carbon dioxide concentrations were higher than today. The model substantially underestimated just how high temperatures would go. When the researchers adapted the model to include the effects of long-term climate changes in vegetation and ice sheets, they were able to get a much closer representation of the warming in the Pliocene era.

The team found that it took much lower concentrations of atmospheric carbon dioxide to recreate the Pliocene’s warm climate than current models — which consider only the relatively fast-adjusting components of the climate — predict. Pliocene carbon dioxide levels are estimated to have been around 400 parts per million by volume (ppmv), while according to current simulations it would take 500 to 600 ppmv of carbon dioxide to bring about the warm temperatures of the Pliocene. As a result, the researchers estimate that Earth’s response to elevated concentrations of is 30 to 50 percent greater than previously calculated. In other words, the climate is more sensitive to carbon dioxide than we thought.

This higher sensitivity of the climate should be taken into account, the team concludes, when targets are set for limiting greenhouse gas emissions. The results of the study appear in Nature Geoscience.

Explore further: Likely near-simultaneous earthquakes complicate seismic hazard planning for Italy

More information: [1] Daniel J. Lunt et al., "Earth System Sensitivity Inferred from Pliocene Modelling and Data,” Nature Geoscience, Vol. 3, No. 1 (2010). www.nature.com/ngeo/journal/v3/n1/abs/ngeo706.html

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peteone1
1.9 / 5 (7) May 05, 2010
I wonder if this "study" used fudged data from AGW zealots at East Anglica University?
TegiriNenashi
1.2 / 5 (5) May 05, 2010
"...the atmosphere and oceans spend a few years or decades adjusting and reaching a balance..." Few years, or decades -- that is a pretty big uncertainty! How can they tell with straight face that the earth "is expected to warm Earth by about 3 degrees Celsius (5 degrees Fahrenheit),"???
JerryPark
2.9 / 5 (8) May 05, 2010
Based on new computer models (which may have no ability to predict anything) scientists estimate the CO2 has double the ability to create higher global temperatures. This despite the fact that current models have failed to predict temperatures.

Estimates based on unvalidated models are just wild guesses.
lewando
1.7 / 5 (7) May 05, 2010
I am surprised that the sensitivity of the climate to CO2 has been misunderstood for so long. I thought that words and phrases like "consensus" and "the debate is over" were used by scientoids--cocksure of their authority--to signal us not to look behind the curtain. It is refreshing to see an actual scientist willing to point out defects in the knowledge base. There may be hope yet but, unfortunately, not for our perpetually obsolete models.

omatumr
1.6 / 5 (7) May 06, 2010
How sad it is to read the suggestion that "targets . . . for limiting greenhouse gas emissions" should be based on such vague analysis.

Was the conclusion a condition for receiving public funds?

Oliver K. Manuel
jsa09
2.8 / 5 (4) May 06, 2010
I am wondering if other gases are included in the models of if they only focus on the one gas. Methane for example is a significantly greater "green-house" gas than Co2 and if it is not considered then the Co2 figures could be an order of magnitude wrong.