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[jonnyv]

Climateprediction.net scientist and former Project Coordinator Dr. David Frame is on a new paper published in the 20 April '06 issue of the science journal 'Nature' entitled 'Climate sensitivity constrained by temperature reconstructions over the past seven centuries.' The abstract follows: The magnitude and impact of future global warming depends on
the sensitivity of the climate system to changes in greenhouse gas
concentrations. The commonly accepted range for the equilibrium
global mean temperature change in response to a doubling of
the atmospheric carbon dioxide concentration1, termed climate
sensitivity, is 1.5–4.5 K (ref. 2). A number of observational
studies3–10, however, find a substantial probability of significantly
higher sensitivities, yielding upper limits on climate sensitivity of
7.7K to above 9 K (refs 3–. Here we demonstrate that such
observational estimates of climate sensitivity can be tightened if
reconstructions of Northern Hemisphere temperature over the
past several centuries are considered. We use large-ensemble
energy balance modelling and simulate the temperature
response to past solar, volcanic and greenhouse gas forcing to
determine which climate sensitivities yield simulations that are
in agreement with proxy reconstructions. After accounting for
the uncertainty in reconstructions and estimates of past external
forcing, we find an independent estimate of climate sensitivity
that is very similar to those from instrumental data. If the latter
are combined with the result from all proxy reconstructions,
then the 5–95 per cent range shrinks to 1.5–6.2 K, thus substantially
reducing the probability of very high climate
sensitivity.

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Source: climateprediction.net
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