Nice piece by Matt Ridley.
Mr. Lewis tells me that the latest observational estimates of the
effect of aerosols (such as sulfurous particles from coal smoke) find
that they have much less cooling effect than thought when the last IPCC
report was written. The rate at which the ocean is absorbing
greenhouse-gas-induced warming is also now known to be fairly modest. In
other words, the two excuses used to explain away the slow, mild
warming we have actually experienced—culminating in a standstill in
which global temperatures are no higher than they were 16 years ago—no
longer work.
In short: We can now estimate, based on observations,
how sensitive the temperature is to carbon dioxide. We do not need to
rely heavily on unproven models. Comparing the trend in global
temperature over the past 100-150 years with the change in "radiative
forcing" (heating or cooling power) from carbon dioxide, aerosols and
other sources, minus ocean heat uptake, can now give a good estimate of
climate sensitivity.
The conclusion—taking the best observational
estimates of the change in decadal-average global temperature between
1871-80 and 2002-11, and of the corresponding changes in forcing and
ocean heat uptake—is this: A doubling of CO2 will lead to a warming of
1.6°-1.7°C (2.9°-3.1°F).
This is much lower than the IPCC's current best estimate, 3°C (5.4°F).
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