Nigel Calder reports on a paper by Dragić et al.. The paper considers the effects of Forbush decreases - when solar flares cause reductions in the number of galactic cosmic rays reaching the Earth. According to the Svensmark hypothesis, this should cause a reduction in cloudiness.

Dragić and his co-authors have looked at the diurnal temperature range - the difference between daytime maxima and nighttime minima after Forbush increases. If clouds are indeed reduced, then the diurnal temperature range should increase, ie colder nights and warmer days.

The results look good for Svensmark's ideas.

The results [are] hard (impossible?) to explain by any mechanism except an influence of cosmic rays on cloud formation.

(H/T Pharos in Unthreaded)