Do solar variations change climate?



Most specialists now agree that the average temperature at the Earth's surface has increased by about half a degree Celsius since the beginning of the 20th century. The cause of this global warming, however, is a matter for intense debate and controversy, ranging from one extreme attributing it all to the increasing greenhouse effect brought about by human activities, to the opposite position attributing the warming to natural climate variability. Some model calculations have shown that the greenhouse effect can account for the size of the observed temperature increase, but the models are still relatively crude and cannot account for the shape of the increase. As a result, most researchers now think that some combination of natural and anthropogenic causes is at work.