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Global Dimming and Brightening
Volume 10, Number 7: 14 February 2007

Gerald Stanhill of the Institute of Soil, Water and Environmental Sciences at the Volcani Center in Bet Dagan, Israel, raises some questions of real concern in the 30 January 2007 issue of EOS - the "Newspaper of the Earth and Space Sciences" that is published weekly by the American Geophysical Union - which questions are intended, in his words, "to draw attention to the challenge that recently reported changes in solar radiation at the earth's surface, Eg↓, pose to the consensus explanation of climate change."

Stanhill begins his short treatise by noting there was "a widespread reduction in solar radiation at the earth's surface, often referred to as global dimming," which "lasted from the mid-1950s until the mid-1980s when a recovery, referred to as global brightening, started." This dimming over the land surface of the globe led to a 20 W/m2 reduction in Eg↓, between 1958 and 1992, which negative shortwave forcing, in his words, was "far greater than the 2.4 W/m2 increase in the positive longwave radiative forcing estimated to have occurred since the industrial era as a result of fossil and biofuel combustion," which latter forcing, he notes, is "what provides the consensus explanation of global warming."

Reporting that "the cause of these large changes in Eg↓, is not known," but that they totally dwarf the change in longwave radiative forcing claimed to be responsible for 20th-century global warming, Stanhill goes on to further report that "no reference to these findings has appeared in the three massive IPCC [Intergovernmental Panel on Climate Change] assessment reports published during the past 15 years," which glaring omission, in his words, "is surprising in view of the important practical consequences of changes in Eg↓, in addition to their theoretical significance for climate change."

Continuing with this line of reasoning, Stanhill contends that "the omission of reference to changes in Eg↓, in the IPCC assessments brings into question the confidence that can be placed in a top-down, 'consensus' science system that ignores such a major and significant element of climate change," which leads him to suggest that "a separate and more fundamental question is whether scientific understanding of climate change is now sufficient to produce a useful consensus view," as we currently have people "asking questions that can be stated in the language of science but that are currently beyond its ability to answer."

We agree with Stanhill's concerns, and contend that until the two-stage global dimming and brightening phenomenon - which involves much greater changes in earth's surface radiative energy balance than that provided by all anthropogenic-induced changes in greenhouse gas concentrations since the start of the Industrial Revolution - can be satisfactorily explained, there is no compelling reason to put any faith whatsoever in what today's climate models imply about the future. And if we have no reason to believe what they suggest, why should we even entertain the foundationless pronouncements of the vast array of politicians who pontificate upon the subject?

Sherwood, Keith and Craig Idso

Stanhill, G. 2007. A perspective on global warming, dimming, and brightening. EOS, Transactions, American Geophysical Union 88: 58.