Global dimming and brightening more complex than previously thought

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http://www.agu.org/cgi-bin/highlights/highlights.cgi?action=show&doi=10.1029/2008JD011263&jc=jd

Editors' Highlight

Global dimming and brightening more complex than previously thought

Several studies show evidence of a widespread decrease in solar radiation reaching the Earth's surface from the 1960s through about the early 1990s. Termed "global dimming," this decrease was followed by "brightening" during the late 1990s. Past efforts correlated brightening trends to decreases in atmospheric aerosol concentrations due to successful environmental regulations and recovery from the Mount Pinatubo eruption. To learn more about the mechanics of dimming and brightening, Long et al. (2009) studied observations of shortwave radiation collected by the U.S. government at 12 surface sites across the United States. These data, aggregated into all-sky and clear-sky surveys, show that widespread brightening occurred over the continental United States during the past 12 years at rates higher than previously thought. The authors found that changes in aerosol concentrations and other direct effects cannot fully explain the observed changes in shortwave radiation. They showed that decreases in cloudiness, which may be indirectly influenced by decreasing aerosol concentrations, have played a significant role in observed brightening patterns. Further, they suggested that the causes of global brightening are complex and are best studied locally or regionally, rather than on a global or continental scale.

http://dx.doi.org/10.1029/2008JD011263">View abstract

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[OKIsItJustMe]

1. How well do IPCC-AR4/CMIP3 climate models simulate global dimming/brightening and twentieth&#8...

http://www.agu.org/journals/jd/jd0907/2008JD011263

How well do IPCC‐AR4/CMIP3 climate models simulate global dimming/brightening and twentieth‐century daytime and nighttime warming?

Martin Wild

Institute for Atmospheric and Climate Science, ETH Zurich, Zurich, Switzerland

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Observations indicate that greenhouse induced twentieth‐century warming has been strongly modulated by variations in surface solar radiation. Between the 1950s and 1980s, declining surface solar radiation (“global dimming”) likely caused a dampening of global warming, whereas increasing surface solar radiation (“brightening”) may have contributed to the rapid warming in the last 2 decades, and possibly also in the first half of the twentieth century. This is also reflected in the decadal evolution of diurnal temperature range, which is highly correlated with surface solar radiation, and which shows a distinct transition from a strong decrease between the 1950s and 1980s, toward a leveling off thereafter. The present study investigates to what extent these effects are simulated in the latest generation of global climate models used in the fourth Intergovernmental Panel on Climate Change (IPCC) assessment report (AR4) (phase 3 of the Coupled Model Intercomparison Project (CMIP3) models). While these models reproduce the overall twentieth century warming over global land surfaces well, they underestimate the decadal variations in the warming and particularly also in diurnal temperature range, indicative of a lack of decadal variations in surface solar radiation in the models.

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Received 29 October 2008; accepted 28 January 2009; published 1 May 2009.

Citation: Wild, M. (2009), How well do IPCC‐AR4/CMIP3 climate models simulate global dimming/brightening and twentieth‐century daytime and nighttime warming?, J. Geophys. Res., 114, D00D11, doi:10.1029/2008JD011372.

[Fresh_Start]

2. rather amazing that global dimming was almost

sufficiently an offset for warming until we improved improved regulations to reduce emissions from cars and smokestacks.

I'm not sure if it was this article or something else I read that attributed our emissions to causing the multi decade drought in Africa (the emissions caused dimming which affected ocean temperature which affected prevailing currents which......)