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The Sun is Getting Restless

NASA's Solar Dynamics Observatory (SDO) captured this image of a very long solar filament on Dec. 6. According to NASA, "Filaments are elongated clouds of cooler gases suspended above the Sun by magnetic forces. They are rather unstable and often break away from the Sun." Credit: NASA

If you find that the Earth is warming up, the first place to look for a cause is the sun. Even though it's 93 million miles away — so far that light takes a full eight minutes for a sunbeam to get here — the incredible energy from what is essentially a thermonuclear explosion that's been going on for billions of years so far is our main source of energy. Even the fossil fuels we use for heat, transport and electricity ultimately come from the sun, since they're made mostly from plants that drew sustenance from solar energy eons ago. 

As it turns out, careful measurements of the sun's energy output over the past several decades have shown that the sun hasn't gotten appreciably brighter, even as global temperatures have continued to rise, so that's not the explanation (which is one more reason climate scientists are convinced human-generated greenhouse glases are to blame). Or to be more precise: the sun has gotten brighter, but then it has gotten dimmer again. And then brighter. And then dimmer. This well-known behavior is tied in with the 11-year solar cycle, which is most notable for the waxing and waning of sunspots. When the sun reaches the so-called solar maximum, sunspots are most numerous; solar flares arc up above the star's fiery surface; blobs of hot particles spew out into space and the sun itself gets a bit brighter. During a solar minimum, the spots become sparse and everything else dials back a bit.

We've just left the most recent solar minimum, and a few gorgeous new satellite images show what a more active sun looks like. One shows a giant arc of hot plasma that's just been spotted erupting from the sun by NASA's Solar Dynamics Observatory).

NASA video of the magnetic filament snaking around part of the sun, stretching more than 700,000 kilometers. Credit: NASA's Solar Dynamics Observatory.

Another comes from the STEREO mission, a pair of spacecraft that watch the sun from two different angles at once to get images of the sun in 3-D.

There's all sorts of science in these images, but for climate-watchers the big question — still unanswered — is whether solar cycles have begun to change somehow. It's happened before: during the 1600s, the sun went into a decades-long decline known as the Maunder Minimum, where there were very few sunspots at all, and presumably (although there was no way to measure it at the time), the sun cooled off. It's probably no coincidence that the Minimum overlapped part of the Little Ice Age, during which Europe experienced unusually cool summers and very harsh winters. But that period of cooling began centuries earlier, so at best it only explains part of what was going on. Still, a study last spring showed that temperatures in Europe, at least, do respond to sunspot changes.

Even now, climate scientists think that a small part of the current warming episode can be attributed to changes in overall solar brightness over the past century, outside of the normal solar cycle. For most of the warming, greenhouse gas emissions are the most plausible explanation. But if the sun should enter a new Maunder Minimum — and it's too early to know whether the current solar wakeup rules that out — that could affect projections of where temperatures will be headed during the coming century. (So, for that matter, would a massive volcanic eruption that would throw huge amounts of dust in the air, block the sun and counteract global warming).

Neither of these scenarios is part of mainstream climate models, for the very good reason that there's no reason to expect them to happen in the next century. That's not the same as a certainty that they won't, though.

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