On Cosmic Rays and Clouds
By Ed Caryl
There have been several papers and articles recently about Svensmark’s theory that claim cosmic rays produce cloud nuclei, which in turn produce clouds that affect the Earth’s climate. My recent article showed the relationship between atmospheric transmission, the Earth’s albedo, and temperature.
Photo by Krish Dulal.
If cosmic rays produce micro-particles that grow into cloud nuclei, and if these particles are large and numerous enough to interfere with sunlight, it should be possible to show a relationship between cosmic rays and atmospheric transmission, and thus clouds.
Relationship between albedo and atmospheric transmission
The transmission is measured in a clear-sky situation. Albedo reflection is mostly from clouds. If aerosols impede transmission and aerosols ultimately produce clouds, then there should be a relationship.
Figure 1: Relationship between albedo and atmospheric transmission.
The problem with Figure 1 is that we only have a few annual data points for albedo. There isn’t a single database for global cloudiness with any temporal extent other than the above data. Two of the points are due to a volcanic eruption. Without those points only a slight relationship remains.
Figure 2: Relationship between albedo and atmospheric transmission after subtracting the two years of Pinatubo volcanic dust.
This result seems to suggest that only large dust and sulfate particles make much difference to clouds and albedo. This may explain the next result.
Figure 3: Monthly data plot of atmospheric transmission and the Oulo, Finland neutron count proxy for cosmic rays. Source of neutron data here.
The problem with this plot is that the volcanic eruptions just happened to occur at negative cycles of the neutron count. We know (or are at least fairly certain) that volcanoes and cosmic rays are not related in any way. For that reason, in the next plot, data from the two years after each volcanic eruption was deleted to avoid a false appearance of correlation.
Figure 4: Monthly data plot of atmospheric transmission versus Oulu neutron count.
Without the volcanic activity in the plot there is no relationship between atmospheric transmission and cosmic rays as measured by the neutron count at Oulu, Finland. The R-squared value is below 0.01, and in the wrong direction. The relationship is completely random.
This result does not necessarily falsify Svensmark’s theory. There may be an explanation as to why cosmic ray flux does not show up in atmospheric transmission. As suggested above, perhaps the particles are too small, or too infrequent compared to other aerosols, but it is another mystery that demands an explanation.