text: The sun has both direct and indirect effects on our climate. Solar activity changes on cycles of 11 years and longer. When the sun is more active it is brighter and a little hotter. More important though are the indirect effects. Ultraviolet radiation increases much more than the brightness and causes increased ozone production, which generates heat in the high atmosphere that works its way down, affecting the weather. Also, an active sun diffuses cosmic rays, which play an important role in nucleation of low clouds, resulting in fewer clouds. In all these ways the sun warms the planet more when it is active. An active sun in the 1930s and again near the end of the last century helped produce the observed warming periods. The current solar cycle is the longest in over 100 years, an unmistakable sign of a cooling sun that historical patterns suggest will stay so for decades.