Global warming skeptics everywhere are jumping on the solar bandwagon: “It’s not greenhouse gases, it’s the sun! Let’s burn some coal to celebrate!”
There are, of course, many, many problems with the solar theory as an explanation for recent warming. To me, the most damning is that the correlation has failed in the last few decades. As highlighted in an interesting news item in this week’s Science:
[Courtillot] and his team acknowledge that “anomalous warming” in the past 2 decades apparently cannot be linked to solar or geomagnetic activity, although they decline to ascribe it to greenhouse gases.
On the other hand, the mainstream theory that today’s warming is caused by carbon dioxide (along with other anthropogenic effects and known natural variability) provides an explanation not just for the “anomalous warming,” but for just about every climate variation over the last 100 million years.
In addition, the solar activity theory doesn’t solve any of the few remaining problems with our standard theories of how the atmosphere operates. For example, it is well known that the tropical upper troposphere has not warmed as much as would be expected from the observed surface warming. But the solar theory provides no explanation to resolve this discrepancy. Thus, those that reject carbon dioxide as an explanation because of the upper troposphere temperature trends must also reject the solar activity theory. For more on the problem of the upper troposphere, see this RealClimate post. (See also Ray Pierrehumbert’s dissection of Courtillot’s theory here and here).
As a scientist, I’m always looking for the most parsimonious explanation for a physical phenomenon. If a single, physically reasonable explanation works, why invoke an entire menagerie of explanations, each more dubious than the last? That’s why the IPCC concluded that greenhouse gases are very likely responsible for most of the recent warming. And that’s why virtually all climate scientists agree with the IPCC reports.
[An unrelated note: the article also describes Courtillot as “one of a handful of credible scientists who reject IPCC’s bottom line.” They apparently don’t find the “Inhofe 400” credible, either.]