Doubling of CO2 likely to result in 2.2 to 4.8 degrees Celsius warming
By Summit Voice
SUMMIT COUNTY — Climate scientists know that greenhouse gases like carbon dioxide and methane trap heat in the atmosphere, but there’s still some uncertainty about how the overall system responds to varying levels of those gases.
By studying the paleoclimatic record, researchers have been able to measure relationships between past greenhouse gas increases and temperatures to some degree, and new research is helping them evaluate past climate sensitivity data to help improve comparison with estimates of long-term climate projections developed by the Intergovernmental Panel on Climate Change.
The scientists found that the likely range of climate sensitivity consistently has been of the order of 2.2 to 4.8 degrees Celsius per doubling of CO2, which closely agrees with the IPCC estimates.
The sensitivity of global temperature to changes in the Earth’s radiation balance (climate sensitivity) is a key factor for understanding past natural climate changes as well as potential future climate change.
The team of international scientists, including Eelco Rohling, Professor of Ocean and Climate Change at the University of Southampton, have developed a more consistent definition of climate sensitivity in prehistoric times. The team discovered that the wide range of climate sensitivity estimates was almost entirely due to the fact that different researchers used different definitions.
“Consistent intercomparison is a top priority, because it is central to using past climate sensitivity estimates in assessing the credibility of future climate projections,” said Rohling, who is currently based at the National Oceanography Centre Southampton but will join the Australian National University.
“Once we had developed the framework and we had elaborated all the different assumptions and uncertainties, we applied it to climate reconstruction data from the last 65 million years. This caused a much narrower range of estimates, and this range was now defined in such a way that we could directly compare it with estimates in the IPCC assessment for their longer-term (several centuries) outlook.”
“Our study only documents what the climate sensitivity has been over the last 65 million years, and how realistic the estimates of the IPCC are in that context,” Rohling said. “It finds that those estimates are fully coherent with what nature has done in the (natural) past before human-based effects. Hence, it strongly endorses the IPCC’s long-term climate projections based on such values: nature shows us it always has, and so likely will again, respond in a way close to what the models suggest, as far as warming is concerned.”