Added Significance of the Climate Forcing of Aerosols and Ignored Consequences of Their Study with Respect to Human-caused Climate Change

A new article on the direct radiative forcing effect of aerosols has appeared in Nature on December 22. Its title is “Global estimate of aerosol direct radiative forcing from satellite measurementsâ€? authored by Nicolas Bellouin, Olivier Boucher, Jim Haywood and M. Shekar Reddy.

The article, unfortunately, perpetuates the inappropriately narrow focus on the globally averaged radiative forcing of CO2. It avoids highlighting the major importance of the spatially heterogeneous radiative forcing of the aerosols. This forcing necessarily results in regional diabatic heating of the troposphere, which would not occur without the human input of these aerosols. A change in time in heterogeneous atmospheric forcing is central to the issue of climate change, and is not captured by a limited focus on global warming. We will post our submitted peer reviewed paper that quantitatively documents the importance of this heterogeneous diabatic forcings from aerosols on the Climate Science weblog as soon as we can.

The abstract of the Bellouin et al Nature article states,

“Atmospheric aerosols cause scattering and absorption of
incoming solar radiation. Additional anthropogenic aerosols released into
the atmosphere thus exert a direct radiative forcing on the climate
system. The degree of present-day aerosol forcing is estimated from
global models that incorporate a representation of the aerosol cycles. Although the models are compared and validated against observations,
these estimates remain uncertain. Previous satellite measurements of the
direct effect of aerosols contained limited information about aerosol
type, and were confined to oceans only. Here we use state-of-the-art
satellite-based measurements of aerosols and surface wind speed to
estimate the clear-sky direct radiative forcing for 2002, incorporating
measurements over land and ocean. We use a Monte Carlo approach to account
for uncertainties in aerosol measurements and in the algorithm used.
Probability density functions obtained for the direct radiative forcing at
the top of the atmosphere give a clear-sky, global, annual average of -1.9
W m-2 with standard deviation, 0.3 W m-2. These results suggest that
present-day direct radiative forcing is stronger than present model
estimates, implying future atmospheric warming greater than is presently
predicted, as aerosol emissions continue to decline.�

The news media has quickly reported on this study, e.g. from the Guardian

An excerpt from that study, headlined “Pollutants ward off global warming, study findsâ€? alludes to the vulnerability paradigm that has been highlighted in our research and reported on the Climate Science weblog. The excerpt from the news article states,

“Earlier this year, Peter Cox at the Centre for Ecology and Hydrology in
Winfrith, Dorset, warned that if the cooling effect of aerosols turned out
to be greater, it could trigger faster global warming.

“It’s quite a bizarre thing, because the last thing you want to suggest to
people is that it would be a good idea to have dirty air, but as far as
climate change is concerned, that’s right. Everyone would be getting
asthma, but the environment would be cooler.

That said, the direct effects of air quality, particularly in urban
areas, are so important to human health, that it would be crazy to think
of anything other than health damage,’ he said.â€?

That quote by Peter Cox, who I have a great deal of respect for, captures the concept of vulnerability and of prioritizing threats to important societal resources (in thus case human health) that we published the paper entitled “A new paradigm for assessing the role of agriculture in the climate system and in climate changeâ€? Rather than focusing almost exclusively on the gloabally averaged radiative effect of CO2, we need to not only consider the heteogeneous climate forcing of aerosols, but also the broader range of environmental threats we face.

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