But actual temperatures have not cooperated with the computer models. Temperature records show a rise of 0.5 degree Celsius over the century, peaking before 1940. In 1610 Galileo began the telescopic observations of sunspots that make up our modern view of the sun.
Sunspots are cooler, darker areas of strong magnetic fields.
The number of sunspots peaks and the direction of the field changes every 11 years or so, making a 22-year magnetic cycle. In the 1980s NASA satellites collected data that showed the sun was brightest during peak sunspot periods. The chart nearby illustrates how the sun's changes, marked by sunspots, may affect climate. Changes in the length of the magnetic cycle and in Northern Hemisphere land temperatures are closely correlated over three centuries. If the recent NASA data are indicative, those changes in the sun's magnetism would track changes in the sun's brightness, for which direct measurements are lacking.