See Spot. See Spot Cool.

Another question from the ever-curious Papou [paraphrased]: I've been reading about the cycle of sunspot activity, and how some believe it connects to climate change. What are your thoughts on this?

Let's start off by discussing sunspots. The sun is essentially a big ball of plasma, a state of matter that's particularly good at holding electromagnetic fields. Under certain circumstances, some magnetic field lines in the sun will bunch together, and change the flow of particles around a spot. This causes the spot to cool enough to appear dark:

Getty Images via Scientific American

In the 1890s, an astronomer couple named Annie and Edward Maunder noticed that there was an unusually low number of sunspots during the years 1645 to 1715, which came to be known as the Maunder Minimum. That period is also known as the Little Ice Age*, due to the unusually cold weather. Some people draw a link between these two, and suggest that sunspot activity is responsible for changes in global climate.

In cases like this, it's important to remember the science adage, "correlation does not imply causation." This means that just because two quantities change in a similar way, it does not mean that one causes the other. Obviously, if one thing causes another, they will be correlated, but you need more than that to prove causation: You need to explain how they're linked, and show that that explanation is backed up by data.

Sunspots actually fail on both counts: Sunspots are dark because they're cooler than the rest of the sun. The Little Ice Age, though, happened during a minimum in the number of sunspots, and tracking the temperature through time shows little correlation:

Wikipedia

While it's important to consider alternate theories to popular beliefs, it's also important to discard them when they are shown to be inaccurate. As I discussed several months ago, I am not an expert in climate science, so I defer to the vast majority who identify CO2 emissions as the leading cause.

*Nifty cultural note unrelated to Physics: Charles Dickens is largely credited with giving us our collective image of a white Christmas through his story A Christmas Carol. Christmases that include snow, however, are quite rare, and it's likely that Dickens only imagined it this way because he grew up at the end of the Little Ice Age, where they were more common.