Global climate change: sunspots revisited.

For nearly two centuries, scientists have speculated about the possible effect of sunspots on global climate, but the mechanism that might be involved has remained a matter of considerable controversy. A central question is how total solar irradiance - the amount of energy received by the earth from the sun - is affected by sunspot activity, which follows an 11-year cycle.

It has been commonly assumed that total solar irradiance would decrease as the number of dark sunspots increased. Direct satellite measurements of irradiance, however, have shown just the opposite to be the case. This means that given more sunspots, more energy is delivered to the atmosphere and global …