Scientific Method —

The Maunder Minimum is back! (Maybe. And we probably won’t notice)

A press release gets lots of people shouting "what do you think now, scientists?"

A new ice age is not actually coming. But you wouldn't know that based on headlines from places like The Telegraph. The "reasoning" behind the headlines is that a new study suggests the Sun is headed for a severe low in its activity, and the last time that happened coincided with a cold period called the Little Ice Age. Ergo, another one is on the way.

Pretty much every aspect of this reasoning is wrong.

To understand why, we have to understand sunspots. Sunspots are the product of magnetic activity inside the Sun, and they appear as darker, cooler areas on the star's surface. You might think that they would cause less light to reach Earth, but the areas around the sunspot brighten up, more than compensating for the dark areas. As a result, there's a simple relationship: the more sunspots, the more solar output reaches Earth.

Normally, sunspots come and go with the 11-year long solar cycle—more during peak activity, less during the Sun's quieter times. But superimposed on that cycle are longer-term trends in activity that we don't understand very well. For example, solar activity has been trending downward since the 1980s, and it's not entirely clear why. But it's still much more active than it was during a roughly 70-year period around 1700, when the Sun experienced what's called the Maunder Minimum, with very few sunspots visible the entire time.

That period happened to coincide with the Little Ice Age, which saw global temperatures dip and glaciers advance, with Europe experiencing notably colder weather. The lack of solar activity provided a nice explanation for this, so the two were assumed to be connected.

Why is this topic back in the news? Blame can be assigned to a press release put out by the Royal Astronomical Society. The release described a talk that would be taking place at the organization's National Astronomy Meeting, focusing on a new model of solar activity. The model, based on a more complex version of the Sun's internal magnetic dynamo, suggests that there are two cycles going on at the same time. When they're in alignment, the solar cycle results in dramatic peaks of activity. When they oppose each other, you get greatly reduced activity—something like a Maunder Minimum.

The people behind the new model say that the Sun is due for a period like this by around 2030. Hence, a new Little Ice Age, at least in the view of some headline writers.

Where does the logic break down? To begin with, meeting presentations generally don't go through rigorous peer review. That doesn't mean they're not interesting or significant, just that the results should be viewed with a bit more skepticism. And the model has only been validated against three cycles—roughly 30 years worth of data. While we don't have magnetic data on the Sun that goes back very far, we clearly have sunspot data back to the 1600s, so the data could have undergone more rigorous validation.

But even if the model does turn out to be right, will it mean a new Little Ice Age? Absolutely not. To begin with, recent work indicates that the drop in solar activity was a relatively minor contributor to that cold period. Instead, volcanic activity seems to have been the major trigger. In terms of the amount of sunlight that reaches the Earth, there's simply not that big of a difference between low- and high-sunspot periods.

In fact, the difference will be completely swamped by the rising impact of greenhouse gasses. At best, a new Maunder Minimum will only reduce the total warming slightly for a brief period.

All good reasons why this sort of breathless coverage shouldn't have been written. But perhaps the strongest reason is that we've been here before; this article is essentially a rewrite of one we published in 2009—the last time that people were talking about a new Maunder Minimum/Little Ice Age.

So why did these articles get written? Presumably because they seem to suggest that climate scientists are in for a big surprise, and the steady diet of warming they've predicted is going to be off the menu. There's a large audience of people who are hoping to hear just that, and the story has been widely circulated among them—we've received at least two requests to cover it. (One of the ironies here is that the "climate skeptic" crowd that is embracing this study also tells us not to trust models of complex systems and doesn't think 150 years worth of temperature data is informative, yet it has latched on to a model validated with 30 years of data.)

The Maunder Minimum is a fascinating area of study given that we still don't know why it happened—or enough about the internal dynamics of the Sun that drove it. But it would be nice if people would stop reading far more into these studies than is justified. If nothing else, it would save us from having to rewrite this story a third time somewhere down the line.

This post originated on Ars Technica

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