Galactic Cosmic Rays vs Global Temperature Oceanographer Paul Farrar (2000) argued that, based on the spatial distribution of the cloud variation during Svensmark's study period, the variation was due to an El Niño which was synchronized with the cosmic ray signal used by Svensmark during the data period of his study. A (2003) critique by physicist Peter Laut of Svensmark's theory reanalyzed Svensmark's data and suggested that it does not support a correlation between cosmic rays and global temperature changes; it also disputes some of the theoretical bases for the theory. Svensmark replied to the paper, stating that "...nowhere in Peter Laut's (PL) paper has he been able to explain, where physical data have been handled incorrectly, how the character of my papers are misleading, or where my work does not live up to scientific standards" Mike Lockwood of the
UK's Rutherford Appleton Laboratory and Claus Froehlich of the World Radiation Center in Switzerland published a paper in 2007 which concluded that the increase in mean global temperature observed since 1985 correlates so poorly with solar variability that no type of causal mechanism may be ascribed to it, although they accept that there is "considerable evidence" for solar influence on Earth's pre-industrial climate and to some degree also for climate changes in the first half of the 20th century. Svensmark's coauthor Calder responded to the study in an interview with LondonBookReview.com, where he put forth the counterclaim that global temperature has not risen since 1999. Later in 2007, Svensmark and Friis-Christensen brought out a Reply to Lockwood and Fröhlich which concludes that surface air temperature records used by Lockwood and Fröhlich apparently are a poor guide to Sun-driven physical processes, but
tropospheric air temperature records do show an impressive negative correlation between cosmic-ray flux and air temperatures up to 2006 if a warming trend, oceanic oscillations and volcanism are removed from the temperature data. They also point out that Lockwood and Fröhlich present their data by using running means of around 10 years, which creates the illusion of a continued temperature rise, whereas all unsmoothed data point to a flattening of the temperature, coincident with the present maxing out of the magnetic activity of the Sun, and which the continued rapid increase in CO2 concentrations seemingly has been unable to overrule.
Galactic Cosmic Rays vs Cloud Cover In April 2008, Professor Terry Sloan of
Lancaster University published a paper in the journal
Environmental Research Letters titled "Testing the proposed causal link between cosmic rays and cloud cover", which found no significant link between cloud cover and cosmic ray intensity in the last 20 years. Svensmark responded by saying "Terry Sloan has simply failed to understand how cosmic rays work on clouds". Dr. Giles Harrison of
Reading University, describes the work as important "as it provides an upper limit on the cosmic ray-cloud effect in global satellite cloud data". Harrison studied the effect of cosmic rays in the UK. He states: "Although the statistically significant non-linear cosmic ray effect is small, it will have a considerably larger aggregate effect on longer timescale (e.g. century) climate variations when day-to-day variability averages out". Brian H. Brown (2008) of
Sheffield University further found a statistically significant (p 3 months) and GCR gave correlations of p=0.06.
Debate updates More recently, Laken et al. (2012) found that new high quality satellite data show that the
El Niño Southern Oscillation is responsible for most changes in cloud cover at the global and regional levels. They also found that galactic cosmic rays, and total
solar irradiance did not have any statistically significant influence on changes in cloud cover. Lockwood (2012) conducted a thorough review of the
scientific literature on the "solar influence" on climate. It was found that when this influence is included appropriately into climate models causal climate change claims such as those made by Svensmark are shown to have been exaggerated. Lockwood's review also highlighted the strength of evidence in favor of the solar influence on regional climates. Sloan and Wolfendale (2013) demonstrated that while temperature models showed a small correlation every 22 years, less than 14 percent of global warming since the 1950s could be attributed to cosmic ray rate. The study concluded that the cosmic ray rate did not match the changes in temperature, indicating that it was not a causal relationship. Another 2013 study found, contrary to Svensmark's claims, "no statistically significant correlations between cosmic rays and global albedo or globally averaged cloud height." In 2013, a laboratory study by Svensmark, Pepke and Pedersen published in
Physics Letters A showed that there is in fact a correlation between cosmic rays and the formation of aerosols of the type that seed clouds. Extrapolating from the laboratory to the actual atmosphere, the authors asserted that solar activity is responsible for approximately 50 percent of temperature variation. In a detailed 2007 post on the scientists' blog
RealClimate, Rasmus E. Benestad presented arguments for considering Svensmark's claims to be "wildly exaggerated". (
Time magazine has characterized the main purpose of this blog as a "straightforward presentation of the physical evidence for global warming".) ==Selected publications==