Saturday, June 10, 2006

Business as usual in 1988

More silly indirection from Pat Michaels, about Hansen's Scenerio A. In essence, Michaels is claiming that Scenerio A was "business as usual" and since nothing was done about greenhouse gases, it should be the reference for checking the accuracy of the 1988 GISS model. You can find links to links at Deltoid, and, of course, we have been blog, blog, blogging along over here at Updike Upper Falls.

However, greenhouse gas forcing has been less than the 1988 business as usual would anticipate, principally because of a flattening of the mixing ratios for methane (CH4), and the chlorofluorocarbons. In the former case economics was the driving force, in the latter, policy as expressed in the Montreal Protocols. We can see this by looking at the NOAA ANNUAL GREENHOUSE GAS INDEX from which the following graphs showing the mixing ratios for CO2, CH4, N2O and the CFCs are taken. In the upper left hand corner of each graph I have put the approximate (2001) amount that each of the greenhouse gases contributes to the forcing.

Clearly, the 1988 business as usual trajectories for methane and the CFCs would have lead to a very different situation than the current one. We can see this in a graph taken from the same source which shows all of the greenhouse gas forcings (a strength of the forcing concept is that it allows a useful comparison of the effect of different greenhouse gases/solar insolation, etc.)

(click to enlarge)
Business as usual would imply that the fairly linear increase in forcing up to 1988 continue. That would imply an additional ~10% forcing today.

(to be continued)

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