February 28, 2007
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FROM VOLUME 8, NUMBER 9, SEPTEMBER 1995
OF GENERAL INTEREST: CLOUDS AND AEROSOLS
"Climate Response to Increasing Levels of Greenhouse Gases and
Sulphate Aerosols," J.F.B. Mitchell, (Hadley Ctr., Meteor. Office,
Bracknell RG12 2SY, UK), T.C. Johns et al., Nature, 376(6540),
501-504, Aug. 10, 1995.
Uses a coupled ocean-atmosphere GCM to simulate past and future climate
since the beginning of the near-global instrumental temperature record, which
includes the radiative effects of sulfate aerosols. The inclusion of aerosols
significantly improves agreement with global mean and large-scale patterns of
temperature in recent decades. Predicts a future warming of 0.2K per decade;
global warming could accelerate as greenhouse-gas forcing begins to dominate
over aerosol forcing. (See related News Note, this issue--Sep. 1995.)
Two related items in Nature, 376(6540), Aug. 10, 1995:
"An Absorbing Mystery," W.J. Wiscombe (Lab. Atmos., NASA-Goddard,
Greenbelt MD 20771), 466-467. Discusses the research context of the following
paper. Cess et al. recently challenged the way climate models treat the
radiative effects of clouds; the following paper shows that the effects proposed
by Cess et al. have less impact than originally suggested. But much greater
attention is needed to the basics of cloud radiative balance before such
uncertainties of current models can be reduced.
"The Variable Effect of Clouds on Atmospheric Absorption of Solar
Radiation," Z. Li (Canada Ctr. for Remote Sensing, 588 Booth St., Ottawa ON
K1V 0J6, UK), H.W. Barker, L. Moreau, 486-490. Examines the effect of clouds
using a four-year global record of solar flux observed from both space and the
Earth's surface. The effect of clouds is highly variable and, contrary to some
recent suggestions, present GCMs should be able to incorporate cloud absorption
into climate simulations.
"Climate Response to Indirect Anthropogenic Sulfate Forcing,"
D.J. Erickson III (Theoret. Studies & Modeling, NCAR, POB 3000, Boulder CO
80307), R.J. Oglesby, S. Marshall, Geophys. Res. Lett., 22(15),
2017-2020, Aug. 1, 1995.
Tests the climatic influence of a cloud albedo change hypothesized to result
from anthropogenic increases in atmospheric sulfur, based on 30-year runs of the
NCAR GCM. The response is strongest in the Northern Hemisphere winter, with
cooling over the North Atlantic and North Pacific oceans on the order of 2-6° C.
Due to changes in the hemispheric wave train, the equilibrium climate does not
cool over central Europe, despite the region's high concentration of sulfate
aerosol. These results may help explain the long-standing issue of what has
caused the observed cooling over the North Atlantic and North Pacific over the
last decades, a feature not explained by increases in greenhouse gases alone.
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