The climate data record has been analysed to look for periodic variations. The origins of several such variations have been identified, for example the Milankovich effect for the ice ages and the thermohaline circulation. This analysis (Ghill, 1991) also showed episodes of several tens to several hundreds of years with no clear geophysical origin. Such periods match variations in the number of sunspots and the concentration of cosmogenic isotopes, i.e. in solar activity, thus opening a new chapter in the study of how the Sun’s activity affects Earth’s climate (Damon and Peristykh, 2004; Muscheler, 2004).