Monday, May 7, 2012


date: Tue, 13 Apr 1999 09:01:48 +0100
from: "Andrew White" <>
subject: Re: HadCM3 CO2 concentrations
to:, "N.W.Arnell" <>, Andrew White <>, Matt Livermore <>, Mike Hulme <>, Sari Kovats <>,,,,

Dear Fast-trackers

I do not think the key findings from the ecosystem group will be effected by
these inconsistencies. Much of the vegetation change and dieback is triggered
by climatic change. The CO2 concetration may effects the magnitude of this
change but not as significantly as the variation in climatic terms.

I am confident that our key results would still hold under the different CO2
concentration scenarios.

Yours Andy White

Mike hulme wrote>>>>>>>>>>>>>>>>>>>>>>>>
Dear Fast-trackers,

In putting the scenario paper together for the GEC issue, John Mitchell and
I have come up with slightly different CO2 concentrations for HadCM2 and
HadCM3 to what we had earlier assumed. These CO2 concentrations will
really have to appear in the scenario paper to be consistent with the GCM
experiments. Given the differences from the values (I think) you have all
used in the impacts work, what significance does this have for your work?

HadCM2 HadCM3
assumed 'correct' assumed 'correct'
2020s 441 470 457 434
2050s 565 590 574 528
2080s 731 770 712 638

The difference is that the assumed HadCM2 concentrations are 20-30ppmv too
low while the assumed HadCM3 concentrations are 20-70ppmv too high.

The assumed HadCM2 concentrations came from Cox and Friend (they had
already run Hybrid with these concentrations before the FT work got under
way, so we adopted their values). I cannot yet trace where the assumed
HadCM3 concentrations came from, but the 'correct' values are what both
John Mitchell and the IPCC (1996 report) have calculated for the IS92a

Your suggestions on how best to handle this inconsistency would be
appreciated. How big a difference do these differences make to your impacts?

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