Testing the proposed causal link between cosmic rays and cloud cover

Institute of Physics Publishing News – April 2008


Cosmic Rays

It is now known that most cosmic rays are atomic nuclei. Most are hydrogen nuclei, some are helium nuclei, and the rest heavier elements.

T Sloan and A W Wolfendale, of the Physics Departments of the University of Lancaster and Durham University, respectively, have published a study casting serious doubt on the supposed link between cosmic rays and cloud cover. The abstract is listed below and the entire paper can be downloaded in PDF format here

Testing the proposed causal link between cosmic rays and cloud cover

Abstract. A decrease in the globally averaged low level cloud cover, deduced from the ISCCP infrared data, as the cosmic ray intensity decreased during the solar cycle 22 was observed by two groups. The groups went on to hypothesize that the decrease in ionization due to cosmic rays causes the decrease in cloud cover, thereby explaining a large part of the currently observed global warming. We have examined this hypothesis to look for evidence to corroborate it. None has been found and so our conclusions are to doubt it. From the absence of corroborative evidence, we estimate that less than 23%, at the 95% confidence level, of the 11 year cycle change in the globally averaged cloud cover observed in solar cycle 22 is due to the change in the rate of ionization from the solar modulation of cosmic rays.

Received 31 January 2008, accepted for publication 14 March 2008
Published 3 April 2008

See also Taking Cosmic Rays for a spin
Pattern of Strange Errors Plagues Solar Activity and Terrestrial Climate Data (pdf)
Damon & Laut, EOS, TRANSACTIONS AMERICAN GEOPHYSICAL UNION, VOL. 85, NO. 39, doi:10.1029/2004EO390005, 2004

The last decade has seen a revival of various hypotheses claiming a strong correlation between solar activity and a number of terrestrial climate parameters. Links have been made between cosmic rays and cloud cover, first total cloud cover and then only low clouds, and between solar cycle lengths and northern hemisphere land temperatures. These hypotheses play an important role in the scientific debate as well as in the public debate about the possibility or reality of a man-made global climate change. Analysis of a number of published graphs that have played a major role in these debates and that have been claimed to support solar hypotheses shows that the apparent strong correlations displayed on these graphs have been obtained by incorrect handling of the physical data. The graphs are still widely referred to in the literature, and their misleading character has not yet been generally recognized. Readers are cautioned against drawing any conclusions, based upon these graphs, concerning the possible wisdom or futility of reducing the emissions of man-made greenhouse gases.

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