Free Death from the Skies! by Ph. D. Philip Plait Page A

the future more energetic eruptions impinge on our atmosphere, we may be able to measure the effects of that as well. That’s just another fun way the Sun can slam us.

CLIMATE OF CHANGE
    With all this talk of magnetic storms, flares, and CMEs damaging the Earth, are we missing something more obvious? The Sun is, after all, far and away the major source of heat in the solar system. While the Sun seems rock-solid in its energy output, we have already established that it’s a variable star. Sunspots wax and wane on an eleven-year cycle; could this possibly lead to a change in the amount of energy we receive from the Sun? And if more or less sunlight hits the Earth, could that then lead to climate change on Earth, and a potential mass extinction?
    It should be noted immediately that time and again, people have tried to tie the Sun’s eleven-year cycle with events here on Earth. The stock market, baseball scores, even personality traits have been (dubiously at best) linked to sunspot numbers. The problem is, if you look at enough cycles, some are bound to line up superficially. You have to be able to separate the wheat from the chaff, which can be very difficult.
    Scientists have been arguing for years over whether there is some correlation between solar activity and weather on Earth. It seems that there is, but the factors involved are subtle and difficult to pin down. If they were clear, there’d be nothing to argue over. However, there are some connections that appear to be firmly in place . . . and sunspots do play a role. But the direction of that role might surprise you.
    Sunspots are dark, cooler patches of the Sun’s surface. You might think, then, that if there are lots of sunspots, we get less light and therefore less heat from the Sun. So, lots of sunspots equals cooler climates.
    But spots are only dark in visible light. There are bright regions surrounding sunspots called faculae (literally, Latin for “little torches”) that form because of the complicated connection between the Sun’s surface magnetic field and the hot gas bubbling up from deeper regions. The gas in the faculae is hotter, and therefore brighter. On average, sunspots are 1 percent darker than the Sun’s surface, but faculae are 1.1 to 1.5 percent brighter. This means that when the Sun is covered in spots, it’s actually brighter in visible light than it is when there are fewer spots!
    The primary source of heat for the Earth’s surface is the visible light from the Sun. Studies have shown that when the Sun is at the peak of its cycle—when sunspots and faculae are more prevalent—the overall solar irradiation of the Earth increases by just about 0.1 percent. This is a small but significant increase—it causes a global temperature increase on Earth of about 0.1 to 0.2 degree Celsius (about 0.2 to 0.4 degree Fahrenheit). The opposite is also true; during the sunspot minimum, the Earth’s average temperature decreases by a fraction of a degree.
    Let’s face it: this is a pretty small effect. By itself, it hardly changes anything on Earth. However, heating of the Earth’s surface from the Sun is only one way the climate can be affected. There are lots of other sources of climate change, as we are now all too aware. In many cases, these sources by themselves don’t do much to the climate.
    But what if two or more of these effects add up?
    Things can get bad. We need only to look back in time a short way to see how.
    The existence of sunspots had been known for centuries, even before the invention of the telescope. But once telescopes were trained on the Sun, the view naturally improved. People have been monitoring the size and number of sunspots nearly continuously since the early 1600s.
    In 1887, an astronomer named Gustav Spörer noticed that the records of sunspots appeared to show an absence of spots between the years 1645 and 1715. For literally seventy years, the Sun’s face was virtually blank, clean of solar acne. In the late