Wednesday, May 9, 2012


cc: t.mitchell
date: Fri Dec 22 16:44:54 2000
from: Mike Hulme <>
subject: query

Tim forwarded your questions to me ..................
[RN] 1. What effect, if any, could aerosol emissions have on the
estimated temperature increases discussed in your report?
[MH] SO2 emissions, and other aerosols, may have some locally meaningful effects on our T
change estimates, but these will be highly scenario dependent. For example, in most of the
new SRES scenarios aerosol concentrations start *falling* globally and for most regions,
thus including aerosol effects may lead to local warming relative to 1990 or 1961-90
climate. Over s and e Asia aerosols increase for a few decades, but then start declining.
It all depends on region, scenario and time-slice. To keep things simple we looked at GG
effects only.
Check out this paper to see one approach to quantifying the regional effects of the SRES
aerosols .........

Schlesinger, M. E., S. Malyshev, E. V. Rozanov, F. Yang, N. G. Andronova, B. de
Vries, A. Gr�bler, K. Jiang, T. Masui, T. Morita, J. Penner, W. Pepper, A. Sankovski
and Y. Zhang (2000) Geographical distributions of temperature change for scenarios
of greenhouse gas and sulfur dioxide emissions. Technological Forecasting and
Social Change, 65, 167-193.

[RN] 2. What effect, if any, could a change in sea currents have on the
estimated temperature increases discussed in your report?
[MH] Our T estimates allow for changes in ocean circulation, as simulated by the current
set of GCM simulations. What you may be getting at is if there are much more dramatic
changes in ocean circulation than have been simulated in a coupled AOGCM. Well of course
in this case some of our country T changes may alter a lot, but this is getting into the
realm of hand-waving - the model simulations that show a much more dramatic slow-down of
THC circulation are either low complexity models or else are high complexity models forced
with arbitrary forcing scenarios (e.g. 4 or 8 xCO2). The latest IPCC TAR comments on some
of these results, but they do represent a significiant outlier compared to where we think
climate is heading in the next 100 years.
Best regards,

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