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Scientists set past climate record straight.

An international team of scientists has developed a new approach for evaluating past climate sensitivity data to help improve comparison with estimates of long-term climate projections developed by the Intergovernmental Panel on Climate Change (IPCC).

The sensitivity of global temperature to changes in the Earth's radiation balance is a key factor in understanding past natural climate changes as well as potential future climate change.

Many palaeoclimate studies have measured natural climate changes to calculate climate sensitivity; but a lack of consistent methodologies has produced a wide range of estimates as to the exact value of climate sensitivity, which has then hindered the results.

The team of international scientists, which includes Eelco Rohling, Professor of Ocean and Climate Change at Southampton University, evaluated previously published estimates for climate sensitivity from a variety of geological episodes over the past 65 million years.

They found that the estimates varied over a very wide range, with some very high values among them, which would imply a very strong temperature response to a change in radiative forcing, for example, due to [CO.sub.2] increase.

The team discovered that the wide range was almost entirely due to the fact that different researchers used different definitions.

Professor Rohling said: "Consistent intercomparison is a top priority, because it is central to using past climate sensitivity estimates in assessing the credibility of future climate projections.

"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."

The scientists found that the likely range of climate sensitivity consistently has been of the order of 2.2 to 4.8[degrees]C per doubling of [CO.sub.2], which closely agrees with the IPCC estimates.

Professor Rohling added: "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. It finds that those estimates are fully coherent with what nature has done in the (natural) past before human-based effects."

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Publication:Environmental Engineering
Geographic Code:4EUUK
Date:Dec 1, 2012
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