26 Feb 2010: Much debate exists about if, in reality, the Earth's cloud cover is impacted by cosmic rays, to what extent, and how that may -- in turn -- impact the Earth's climate. Following are highlights of a post by Dr. Roy W. Spencer on the subject of "Geomagnetic Forcing of Earth's Cloud Cover During 2000-2008." Roy had been working with 9 years of global reflected sunlight data from the CERES instrument flying on NASA’s Terra satellite, he decided to take a deeper look at some data, ... and found results that were "at least a little intriguing." Roy's work took but a few hours and opened his mind to new possibilities...
The following plots show detrended time series of monthly running 5-month averages of (top) CERES reflected shortwave deviations from the average seasonal cycle, and (bottom) monthly running geomagnetic Ap index values from the NOAA Space Weather Prediction Center. As I understand it, the Ap index is believed to be related to the level of cosmic ray activity reaching the Earth. [He addresse
s the reason for detrending in his full article.)
Note that there is some similarity between the two plots. ...[A scatterplot of the data produces an average linear relationship of about 0.05 [Watts] per sq. meter increase in reflected sunlight per 1 unit decrease in Ap index.] This is at least qualitatively consistent with a decrease in solar activity corresponding to an increase in cloud cover.
At face value, ... the geomagnetic modulation of cloudiness has about 10 times the effect on the amount of sunlight absorbed by the Earth as does the solar cycle’s direct modulation of the sun’s output. It also rivals the level of forcing due to anthropogenic greenhouse gas emissions, but with way more variability from year to year and decade to decade. (Can anyone say, “natural climate variability”?)
Dr Spencer's full article
(We will also soon provide a link on a subsequent article in which Roy presents a discussion and data plots that suggest clouds, not CO2, are dominating as a climate driver since 2000.)