There Goes the Sun

Colorado Media Matters recently called out KCOL radio host Keith Weinman for repeating the assertion that global warming is being caused by the sun’s activity.

This “the sun did it” conclusion is often posited by climate skeptics who have steadily seen the scientific basis of their arguments cut out from under them. KCOL’s Weinman shows, if nothing else, that shout radio may not be the best forum to dispute scientific hypotheses.

Weinman said, among other things:

“And the trends on Mars are the same as the trends on the planet Earth. What do Mars and the planet Earth have in common? The sun. That’s all. The sun is a burning ball of hydrogen and it varies in the radiation and the heat that it puts off. It’s not absolutely totally consistent; it has varied over time. And that’s the major, that’s the major thing that’s going on here.”

Weinman noted that there is global warming on Mars that may be the result of changes in solar activity. If he’s going to drag the planets of the solar system into the debate, it’s only fair to include Venus, which has an atmosphere about 95 percent carbon dioxide and a surface temperature of 450 degrees Celsius (842 degrees Fahrenheit).

The earth has an average surface temperature of about 14.4 degrees C (58 degrees F) and Mars minus-53 degrees C (-63 degrees F). Neither Mars nor Venus is much like earth. But fair’s fair. Talk about Mars, talk about Venus. Venus is more like the earth than Mars is. Venus is similar in size, gravitation and composition to earth. It’s believed that Venus once had oceans, which have burned up in the runaway greenhouse that is Venus’s atmosphere.

As we continue to pump greenhouse gases into the atmosphere, while the sun’s output (contrary to what Weinman asserts) remains relatively stable — which we’ll get to in a minute — I’ll leave it to the reader to decide which planet provides the better object lesson.

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Nobody disputes that the sun influences climate. But some recent research attributes a large portion of the modern increase in surface temperature to solar activity. Some global warming skeptics have seized these conclusions as the true culprit behind the warming earth, not man-made increases in carbon dioxide.

In the February 8 , 2007 issues of the Proceedings of the Royal Society A, Danish Space Research Institute’s Henrik Svensmark and colleague argued that when the solar magnetic field weakens, more cosmic rays reach the earth. This increases aerosols that form cloud nuclei. He says, “In 1900 the cosmic rays were generally more intense than now and most of the warming during the 20th Century can be explained by a reduction in low cloud cover.”

In a 2006 contribution to Geophysical Research Letters, Duke University physicist Nicola Scafetta says, “The sun might have contributed approximately 50 percent of the observed global warming since 1900.” Scaffetta’s work reached a wider audience than many solar physicists aspire to when U.S., Sen. James Inhofe (R-Okla.) cited his paper in a speech last fall calling climate change “the most media-hyped environmental issue of all time.”

Climatologists are unimpressed. The IPCC’s Fourth Assessment Report on “The Physical Science Basis” of climate change says, “The peak-to-trough amplitude of the response to the solar cycle globally is estimated to be approximately 0.1

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