A Presentation by V. Ramanathan at the SORCE Meeting entitled “How do Aerosols and Clouds Regulate the Planetary Albedo and the Solar Radiation Budget?”

The 2006 Earth’s Radiative Energy Budget Related to SORCE (the Solar Radiation and Climate Experiment) Meeting is being held this week (September 20-22, 2006) in Washington (see for more information on the meeting). The purpose of this meeting I(which has been announced previously on Climate Science) is

“The theme of the 2006 SORCE Science Team Meeting is The Earth’s Radiative Energy Budget Related to SORCE. Several of the key questions and issues to be addressed include:

What is the present state of knowledge of the Earth’s radiation budget from space, from within that atmosphere, and at the surface?

What are the key processes that control Earth’s albedo?

What are the key radiative forcing agents, of natural and anthropogenic origin, and how have their relative influences changed over the past three centuries?

What are the important feedback mechanisms for regulating Earth’s climate?

What is the sensitivity of climate to induced radiative forcing and over what time scales does climate respond?

What is the role of the biosphere? ”

This week, several of the abstracts for the meeting will be posted and briefly commented on. The one for today (Wednesday) is by V. Ramanathan entitled “How do Aerosols and Clouds Regulate the Planetary Albedo and the Solar Radiation Budget?” [unfortunately, Dr. Ramanthan had to cancel his oral presentation; nonetheless, his abstract is very informative]. Dr. Ramanthan is one of the co-authors of the 2005 National Research Council (NRC) Report
“Radiative forcing of climate change: Expanding the concept and addressing uncertainties.”

The abstract includes the text,

“There is practically no theory for explaining how the cloudy sky albedos are regulated. Given this state of the field, and given the fact that clouds exert a large global cooling effect (about –15 to 20 Wm-2) we need a new approach to cut through the current impasse on this fundamental problem in climate dynamics. On a more practical level, the link between aerosols and cloud albedo produces the so-called indirect effect of anthropogenic aerosols. Many models and field observations (e.g, INDOEX and ACEII) have shown that an increase in anthropogenic aerosols can nucleate more cloud drops and enhance the cloud albedo and lead to a cooling effect. The IPCC-2001 report shows that this cooling effect may be large enough to offset 50% to 100% of the radiative heating due to the build up in greenhouse gases. This
indirect effect (i.e, the regulation of cloud albedo by anthropogenic aerosols) is acknowledged to be the largest source of uncertainty in understanding the human impact on the global climate.”

While Climate Science does not agree that the indirect effect of aerosols is the “largest source of uncertainty in understanding the human impact on the global climate”, it does agree that it is a very significant first-order effect on the climate system, as was also concluded in the 2005 NRC Report. This conclusion also requires that meaningful regulation of human climate forcings must include the human input of aerosols into the climate system. Since aerosol effects involve much more than the indirect effect of aerosols, as defined by Dr. Ramanthan (such as including nitrogen deposition (e.g. see and black carbon deposition (e.g. see), the regulation of aerosols such that they do not significantly affect the climate system is a daunting challenge.

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