It is almost exactly 400 years since Galileo turned his telescope on the sun and saw it to be an imperfect orb covered in spots, quite unlike the teachings of Greek cosmology. If his observations had been made four centuries later, he would have drawn a different conclusion. The sun has recently shed its spots, prompting sceptics to renew their claims that climate change is not anthropogenic but rather heliogenic. Sunspots are a bit of a mystery. They appear as dark patches in the photosphere-the surface layer of the sun-that come and go. Normally the number of sunspots peaks every 11 years, coinciding with times when the sun’s magnetic field is at its strongest. As the field wanes, the number of sunspots falls to a trough at which point the sun’s magnetic field reverses direction and starts to regain its strength. As early as 1801 William Herschel, a British astronomer, suggested that when sunspots were plentiful the Earth would be warmer. He supported his hypothesis by reference to variations in the price of wheat published in Adam Smith’s ‘Wealth of Nations. More recently, solar scientists and climatologists have played down the role that sunspots might play in […]