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The Chilling Stars – Henrik Svensmark & Nigel Calder *****

Every once in a while you come across a book that really makes you think, because it presents a theory that’s a surprise, yet the more you read the text, the more it seems to make sense. The Chilling Stars is just such an book. In it, science journalist Calder and scientist Svensmark put forward a striking case for the argument that cosmic rays – high speed particles from outside the solar system – have a huge impact on our global temperature.
At first sight this seems crazy, and Svensmark and his colleagues had to put up with a huge amount of resistance when they initially came up with their theory, but with time, many observations have raised the likeliness of this theory to something like that of dark matter – one that we aren’t certain of, but has a lot in its favour.
The idea is that these high energy particles (or more precisely the secondary particles that are generated when the cosmic rays impact the atmosphere) act as triggers for cloud formation. When there are a lot of cosmic ray particles getting through, there are more clouds, when there are less cosmic rays there are less clouds. This is significant for climate change because low clouds cool the planet. This is frustrating for climate change modellers because, though mostly recognizing that low clouds do have a cooling effect, climate change models can’t predict cloud effects, so tend to ignore them.
The level of cosmic ray bombardment we suffer is largely in the hands of two mechanisms – the sources out in the galaxy from which the cosmic rays originate, and the Sun. The solar wind provides us with a barrier that significantly reduces cosmic ray impact on the Earth. Variations in both mechanisms have resulted in big changes in the cosmic ray impact on the Earth. Svensmark and his colleagues have evidence that strongly suggests a link between cosmic ray levels and historical warming and cooling. The result is a whole new take on global warming.
Perhaps the only unfortunate aspect of the book is a bitter approach to conventional climate change scientists, who are portrayed as having a vested interest in showing that carbon dioxide levels are the only driver of global warming. It’s particular sad that the book was used as part of the basis for a much criticized and highly unbalanced TV documentary that didn’t do justice to Svensmark’s theories because of its negative attitude to human-caused climate change theories. It seems likely that both mechanisms have contributed to recent climate change effects – and Calder and Svensmark don’t do enough to reflect the increasing reality of climate change impact on the world – but it’s not surprising they are a little defensive after the reception this theory first received. It’s important to stress that this book’s theory could well provide an explanation for the cycles of heat and cold that have happened in the Earth’s past, but that cosmic ray climate change cannot be used in an attempt to dismiss the major contribution of human-caused global warming: this is now pretty well universally accepted.
I would also say, although Calder uses the tricks of a good science writer, bringing in a human touch on a regular basis, The Chilling Stars doesn’t always sparkle as a great popular science book should – but I think the importance of the subject and the fascinating nature of the tie-in of cosmic rays to Earth weather is more than enough to overcome this and make this a well-deserved five star read.
Review by Brian Clegg


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