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Then Again ? Rethinking Climate Change
Hansen, J., Sato, M., Ruedy, R., Lacis, A. and Oinas, V.  2000.  Global warming in the twenty-first century: An alternative scenario. Proceedings of the National Academy of Sciences, USA, Early Edition. Online at www.pnas.org.

What was done
The authors provide their best estimates of radiative climate forcings since 1850 and discuss their implications for past and future climate change.

What was learned
The radiative forcing of the atmospheric CO2 increase experienced between 1850 and 2000, according to the authors, was 1.4 W/m2, which is equivalent to that of all other (non-CO2) greenhouse gases (GHGs).  Also of the same magnitude, but of opposite sign, was the radiative climate forcing attributable to atmospheric aerosols.

What it means
Since fossil fuel use is the main source of both CO2 and aerosols, the authors state that "it follows that the net global climate forcing due to processes that produced CO2 in the past century probably is much less than 1.4 W/m2."  Indeed it is.  Their own estimates, in fact, suggest it would be zero.  "A corollary," as they put it, "is that climate forcing by non-CO2 GHGs is nearly equal to the net value of all known forcings for the period 1850-2000."  Put more bluntly, their conclusion is that essentially all of the radiative climate forcing of the past 150 years was provided by things other than fossil fuel usage.

Assuming this conclusion is correct - and we believe it must be very close to reality - what does that say about the Kyoto Protocol?  Simply that it is absolutely and undeniably unnecessary.  It is, in fact, ludicrous in the extreme to attempt to ameliorate future climate change by regulating activities that have had absolutely nothing to do with the climate change of the entire industrial era.

Reviewed 16 August 2000