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The Effect of Sunspots on the Earth's Climate
Even though sunspots are darker, cooler regions on the face of the sun, periods of high sunspot activity are associated with a very slight increase in the total energy output of the sun. Dark sunspot areas are surrounded by areas of increased brightness, known as plages. Some parts of the solar spectrum, especially ultraviolet, increase a great deal during sunspot activity. Even though ultraviolet radiation makes very little contribution to the total energy that comes from the sun, changes in this type of radiation can have a large effect on the earth's atmosphere, especially the energy balance and chemistry of the outer atmosphere. Though the connection between sunspot activity and the earth's climate is still being debated, it is known that a period of unusually low sunspot activity from 1645-1715, called the Maunder Minimum, coincided with a period of long cold winters and severe cold temperatures in Western Europe, often called the "Little Ice Age."

Drought ImageAccording to Fisher, "It's controversial whether the solar cycle has an effect on the earth's climate. One thing that is known for sure is that solar activity, which is what we call the general feature of having magnetic fields on the sun, changes the sun's luminosity--that is, how much energy is coming out of the sun--on the level of a few tenths of a percent. That could change the earth's climate in this cyclical way, but it's controversial." The controversy is due to the complexity of the earth's climate. It is difficult to disentangle the many factors that contribute to climate change. For instance, how do you separate the effects of global warming from the possible effects incurred by changes in solar activity?

Dearborn is also cautious about ascribing climate effects to sunspot cycles: "People have speculated, but I don't think the connection is absolute yet....there is some speculation that sunspots result in climate effects, but that's a very, very hard area, and one that requires much more research before we can be certain of climate effects."

As far as we can currently tell, variations in the sunspot cycle seem to have far less impact on the earth's climate than human actions, such as burning fossil fuels or clear-cutting forests, do. However, more research into sunspots needs to done. In the next section, you can conduct some of your own research into sunspots.

 


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Observatory  1998 The Exploratorium.