On the Sun as the Cause of Climate Change

So I've reached the point where I've heard enough people tell me that "The Sun is responsible for climate change, and the mainstream view is just another example of alarmist propaganda by the fascist environmental movement!" where I feel like it's necessary to say something about it. Doesn't it seem odd to anyone that the overwhelming majority of people who've studied the climate for their entire lives disagree with a view that's been around for well over a decade, but a significant chunk of the general public still believes it to be true? And doesn't it seem even odder that between the two groups, it's usually only the scientists who've actually read the work on which the solar hypothesis is grounded?

Accordingly, I hereby declare that anyone who wants to say that the Sun is responsible for climate change, and people are not, should have to actually at least some research. To be clear, I have no problem with the view that "The relationship between solar variability and the climate system is poorly understood, and therefore represents an area of considerable uncertainty in climate research." But that's what the alleged "eco-fascists" think. If you're going to take the view that the mainstream is wrong and stupid, I think you should have to at least figure out what the mainstream thinks. Don't worry; I'll help!

The first place to start is the IPCC's very short answer to the question, "Can the Warming of the 20th Century be Explained by Natural Variability?" in Chapter 9 of its report, on pages 702-703. Basically, the IPCC concludes that the 20th century's climate pattern doesn't seem to bear the characteristics that we would expect if it were caused by natural variability, and does bear the characteristics that we would expect from a greenhouse gas driver (in my opinion, the most convincing piece of evidence is the cooling of the stratosphere, but perhaps unidentified and therefore unquantified solar influences on atmospheric chemistry and circulation could be responsible for that).

Because the simple answer won't satisfy anyone, the next step is the IPCC's discussion of "Solar Variability" in Chapter 2 of its report, on pages 188-193, part of its examination of various radiative forcings on the climate system. In it, the IPCC basically says that the direct effect of changes in solar irradiance can't explain the changes we've observed, but we don't really understand all of the indirect effects of the Sun on the climate system. Still, it doesn't seem like the Sun is responsible, because we haven't regularly observed the patterns we would expect to see if it were responsible. So while it's possible that we just don't understand what's really going on, and the Sun really does play a critical role in shaping the Earth's climate, there isn't really any evidence that would be decisive in this regard.

While I think those resources provide a pretty decent summary of the state of the science, I think some people might think that they come off as not really taking the question of solar forcings seriously. Accordingly, a more comprehensive examination of the issue (which is heavily relied on in the IPCC's discussion) can be found in a Hadley Center report on "The Influence of Solar Changes on the Earth's Climate." I haven't read the report myself, but I would assume that it does a good enough job that anyone who really wants to know what mainstream scientists think about the Sun's influence on the climate would be able to find what they're looking for.

I suspect, though, that when they point to the Sun as the cause of climate change, most people are relying on what they've heard about the work of certain scientists, most popular among whom I perceive to be Henrik Svensmark of the Danish National Space Center. Accordingly, it's probably worthwhile to bring up Peter Laut's controversial paper, "Solar Activity and the Terrestrial Climate: An Analysis of Some Purported Correlations," in which Svensmark and others are basically called bad scientists (though with a little more tact) because they manipulated data and used questionable scientific practices in order to justify their conclusions. Laut and Paul Damon published another shorter article titled, "Pattern of Strange Errors Plagues Solar Activity and Terrestrial Climate Data," which basically summarized the pair's earlier work and besought the general public to please stop drinking Svensmark & Co.'s Kool-Aid.

Needless to say, Svensmark & Co. weren't too pleased about this, and responded accordingly. Regarding the first paper, Svensmark released this rebuttal, and after the second one was published, Svensmark and Eigel Friis-Christensen (an important member of Svensmark & Co.) had this to say. The highlight, I think, has to be the conclusion of the latter, which says, "In summary, Laut's methodology consists of first writing false accusations, then totally neglecting the refutations, and finally referencing his very own claims as corroboration when publishing new accusations. This is in our view an interesting, but also the very only, conclusion that can be drawn from the article." So I guess one should take Laut's criticisms with a grain of salt, given the vigor with which they were disputed by their targets. I'm honestly not in a position to evaluate them, given my lack of statistical training. But if you're going to subscribe to Svensmark's views, I do think it's worthwhile to take his detractors into account.

At the end of the day, I don't think it's fair to conclude that the sun is responsible for climate change, and humans are completely innocent. As I wrote in this article, we have every reason to believe that greenhouse gases and other anthropogenic influences have played some role in shaping the state of the climate, and will continue to do so in the future. By the same token, I do think that we would be wrong to completely ignore the possibility that the sun has played more of a role than it's currently given credit for. But to say that the mainstream is espousing propaganda to fuel some sinister agenda because certain physical mechanisms aren't well understood seems flat wrong. That's especially true in light of the lack of any really convincing evidence in favor of the solar hypothesis, and the amount of effort spent to understand the nature of the Sun's influence by the mainstream climate science community.