SENSibility 10: The “Cosmic Ray” Theory of Global Warming Takes a Hit

One of the favourite theories of climate change skeptics is in big trouble.

Danish scientist Henrik Svensmark has championed the idea that global warming is not caused by greenhouse gas emissions, but rather by cosmic rays. Cosmic rays are deflected away from Terry (or the earth, if you must) by the planet’s magnetic field and by the sun’s solar wind. If Svensmark is right, then more cosmic rays will hit Terry when the solar wind is weak, and less when the solar wind is strong. The climate is impacted because as more cosmic rays hit Terry when the sun’s solar wind is weak, they create more charged particles in the atmosphere which in turn creates more clouds which in turn cools the climate. When the sun’s output of solar wind is strong, fewer cosmic rays will hit Terry and the planet will warm up because less cloud cover will form.

So, there should be a correlation between periods when more or fewer cosmic rays were hitting Terry (i.e., when the solar wind is weak or strong) and the formation of cloud cover. However, according to a study by scientists at Lancaster University, there is no such correlation. Cosmic rays, it would appear, make only a very weak contribution to cloud cover formation. Terry Sloan, one of the scientists on the Lancaster team, summed up the implications of the study: “We tried to corroborate Svensmark’s hypothesis, but we could not; as far as we can see, he has no reason to challenge the IPCC – the IPCC has got it right. So we had better carry on trying to cut carbon emissions.”

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