Could Cosmic Rays cause Global Warming?
18 Apr, 2008 06:57 pm
The International Panel on Climate Change (IPCC) has come to the conclusion that it is 90% probable that global warming is caused by man made greenhouse gases largely emitted since industrialisation. This implies that the IPCC estimate that the probability that it is wrong in this conclusion is 10%. Can cosmic rays provide the undiscovered effect?
Can cosmic rays provide the undiscovered effect? In recent years much publicity has been given to the work of two groups of scientists who observed that the amount of low altitude cloud seems to follow the changes in the rate at which cosmic rays fall on the Earth. This led the groups to propose that cosmic ray particles falling on the Earth's atmosphere influence the cloud cover. Is this the New Effect which is needed to produce global warming, assuming that the computer models of the effects of greenhouse gases are wrong?
The observation that the low cloud cover decreases as the cosmic ray rate decreased at the 11 year peak in the solar activity (sun spot maximum) in 1990 led the 2 groups to propose that ionization from cosmic rays is responsible for the production of clouds i.e. less ionization leads to less cloud and vice versa. The rate at which cosmic rays fall on the Earth has been observed to decrease over the past century. So, if cosmic rays produce clouds and there are now fewer cosmic rays we will have less cloud cover than we once had, allowing more of the sun's heat to penetrate to the Earth's surface to produce the observed global warming. If the proposal is true, it implies that we are wasting our time cutting greenhouse gas emissions to combat global warming. We could simply carry on as usual until the cosmic ray rate returns to normal. Hence the proposal has vast significance.
Before we accept this far reaching conclusion we must apply some caution. One cannot accept that one effect causes another just because they occur at the same time. The number of cases of sun burn and the consumption of ice cream both peak in summer but you cannot conclude that eating ice cream causes sun burn. For this reason we set out to try to find further evidence to support the hypothesis that the low cloud cover depends on the rate at which cosmic rays fall on the Earth. and so provide the undiscovered effect needed in the event that the computer climate models are wrong. We made three tests.
The first test we did was to use the shielding effect of the Earth's magnetic field. The modulation of the cosmic ray rate during the 11 year solar cycle depends on the magnetic latitude. We looked to see if the changes in the cloud cover observed by the two groups changed in the same way with magnetic latitude. We found that the low cloud cover was independent of magnetic latitude and so this did not support the hypothesis of the groups. A statistical analysis showed that less than 23% of the changes observed by the two groups can be ascribed to changes in the cosmic ray rate.
The second test that was done was to study the short term increases in the cosmic ray seen during magnetic storms. No corresponding increase in cloud cover was observed as would be expected from the hypothesis of the two groups. The third thing we did was to look to see if the cloud cover decreased during the frequent decreases in the cosmic ray rate known as Forbush decreases. No significant decrease in low cloud cover was observed during these Forbush events although the statistical precision of the observations was poor.
In conclusion, we could find no evidence in support of the hypothesis that changing cosmic ray rates contribute significantly to changing cloud cover and thereby to global warming. Therefore, cosmic rays are not the new effect that would allow us to declare that the IPCC is wrong.
Terry Sloan and Arnold Wolfendale. Based on a recent publication in Environmental Research Letters.