So I decided to use the method I used to earlier investigate a possible solar cycle impact on US temps, to see if I could find a *global* solar cycle signal. Answer? Ehhhhhh (waves flat hand in manner of the universal gesture for “not much there, there.”)
Blue is the average temperature profile (with low frequency component and volcanic signal removed) of temperature anomalies over a solar cycle, in months from minimum, and in red, the average sunspot cycle, standardized to have mean zero and the same standard deviation. If there is a signal of the solar cycle here, it’s highly out of phase and still difficult to find in the noise. To be sure, there is a minimum in temperatures around 32 months after the sunspot minimum and a maximum about fourteen months before, but there are all these random wiggles obscuring any clear relationship even with some lag. Nevertheless, if we essentially “fish” for a signal, we can at least get something that isn’t zero-since the solar brightness does vary, even if climate were highly insensitive to perturbation (moreso than even I think it is) there should be some change from the small variation in solar brightness, and if there are amplifying mechanisms then the sensitivity would have to be very small indeed to accommodate almost no actual temperature change over the solar cycle. So if we make it so the mid points between solar cycle extrema line up with the mid point between temperature extrema, we get a lag of about 45 months, consistent with what we found for the US. And we get a bit of a relationship:
Interestingly, this seems to imply that typical solar cycles have a temperature variation of about .05 K. The IPCC report, and frankly the work of a lot of scientists I respect, cite a number twice this large. The heck gives?
I have a theory. The main cite for the estimate of the solar cycle signal is Douglass and Calder. But Douglass and Calder estimate the magnitude of the solar cycle signal on lower tropospheric temperature. Since variations (though not trends) tend to be larger in the troposphere, it isn’t terribly surprising that there should be a larger signal in the troposphere. I also view the removal of ENSO from climate data increasingly as an erroneous and philosophically wrong approach to signal detection in climate. ENSO is a part of the climate system, it is not in some manner magically immune to radiative forcing. Lastly my approach to accounting for the confounding impact of volcanic eruptions is, I personally believe, superior.
It is worth noting that just because the impact of the sunspot cycle itself, over the short term, is a small effect, does not preclude the possibility of secular trends in solar activity, damped by the oceans thermal inertia, causing long term climate trends. To answer that question we need a full model that accounts for those effects, contains the right sensitivity and response time, and an accurate history of the forcing from all solar effects. These amount essentially to a long list of unknowns.
It’s also worth nothing that if the forcing over the solar cycle is actually rather large, due to a cosmic ray effect on clouds, such a small temperature change would require a low sensitivity or an inordinately high degree of thermal inertia-the latter however is probably inconsistent with relatively short time lags observed for solar and volcanic effects. Of course, even if there weren’t an additional forcing apart from solar brightness alone, such a small signal is compatible with a low sensitivity.