New studies disprove cosmic ray and solar influence theories of global warming

Ecologist 06/02/2009

Get into an argument with a climate change sceptic, and sooner or later they'll trot out the old arguments about it being all due to cosmic rays, or the sun.

Now, two new studies will help you set them straight. An international group of scientists writing in the journal Atmospheric Chemistry and Physics investigated the hypothesis that a reduction in the amount of cosmic radiation hitting the earth reduces the size and number of cloud droplets, which leads to more sunlight reaching the earth’s surface and consequent temperature rise.

Using satellite data, the researchers looked at what happened to cloud droplet size, water content, and depth during so-called ‘Forbush decrease’ events – periods in which the intensity of rays hitting the earth decreases by up to 30%. They could find no statistically significant association between the Forbush events and any of the cloud factors they studied.

‘Reduced cosmic rays did not lead to reduced cloud formation, either during the [Forbush events] or during the days that followed,’ said Professor Jon Egill Kristjansson of the University of Oslo. ‘Indeed, following some of the events we could see a reduction, but following others there was an increase in cloud formation. We did not find any patterns in the way the clouds changed.’

Meanwhile, a Swiss–Russian research team working to reconstruct the temperature record of a Siberian glacier for the last 750 years has concluded whilst there was a strong link between solar activity and the area’s temperature until 1850, they discovered that the rise since 1850 could not be explained by the sun’s behaviour.

Using ice-cores drilled from the Belukha glacier in the Siberian Altai, the team took 3,600 samples of the levels of oxygen isotopes from the ice. The radioactive oxygen atoms give an indication of past temperature.

They discovered that the significant temperature increase of the 20th century could not be explained by solar activity. ‘While changes in the solar activity were a main driver of temperature variations in the pre-industrial period, the temperatures in the Altai have shown a much higher rate of increase than that of solar activity during the past 150 years,’ said Anja Eichler, scientist at the Paul Scherrer Institute. ‘The strong increase in the industrial period, however, correlates with the increase in the concentration of the greenhouse gas CO₂ over this time.

‘The results of our regional study indicate that changes in solar activity explain less than half of the increase in temperature in the Altai since 1850. This agrees with global studies, based on reconstructed northern hemispheric temperatures.'