Sunspots vs Global Temperature

Note: Googling for a graph of global temperature over time? See here.

More fish in a barrel, and indeed fish that have already been shot up quite thoroughly, but I’ve been running into Svensmarxists of late.

According to something called the “Daily Tech”, which is the sort of news site that credits Anthony Watts with being a “meteorologist” (he was a TV weatherman for some time; I don’t know if he has an undergrad degree),

many climatologists now believe solar magnetic activity – which determines the number of sunspots — is an influencing factor for climate on earth

which, as we used to say in calculus class, is true for sufficiently small values of “many”. And apparently the number of sunspots is extraordinarily small of late:

NOAA reversed their previous decision on a tiny speck seen Aug 21, which gives their version of the August data a half-point. Other observation centers such as Mount Wilson Observatory are still reporting a spotless month. So depending on which center you believe, August was a record for either a full century, or only 50 years.

Now, what do those “many” climatologists have to say about sunspots? Apparently (I have trouble keeping this straight) they correlate positively with global mean temperature because…

According to Watts, the effect of sunspots on TSI (total solar irradiance) is negligible, but the reduction in the solar magnetosphere affects cloud formation here on Earth, which in turn modulates climate.

This theory was originally proposed by physicist Henrik Svensmark, who has published a number of scientific papers on the subject. Last year Svensmark’s “SKY” experiment claimed to have proven that galactic cosmic rays — which the sun’s magnetic field partially shields the Earth from — increase the formation of molecular clusters that promote cloud growth.

Now, as an actual meteorology Ph.D. (although it’s a well-known met school it also gave a doctorate to Pat Michaels, so make of this credential what you will), I seem to recall that high clouds warm the surface because of something called the “greenhouse effect”, but as far as I know these people think that is all mumbo-jumbo. So do the high clouds correlate with high temps or low on the Svensmark theory? Wikipedia says that according to Svensmark:

Fewer cosmic rays meant fewer clouds–and a warmer world.

(ref: Svensmark, Henrik, “The Chilling Stars: A New Theory of Climate Change”, Totem Books, 2007 (ISBN 1-840-46815-7)

[Update: Dano helpfully points out in the comments that we have already performed the experiment, and it does look like the main effect of contrails, which are high clouds, is greenhouselike; removing them caused a detectably larger diurnal temperature cycle and detectably decreased temperature.]

Oh well. Have it your way. So according to this, since sunspots cannot be lower than they are now, we should be seeing the coldest summer of the century, right? (Less solar magnetism, more cosmic rays, more clouds, cooler temperatures goes the “argument”, I gather.) Well, August data is not in, but July is not looking good for Svensmark.

And while the current year to date is a bit below the trend line (largely owing to a La Nina event), it remains more on the warm side than on the cool. So what on earth could cause these people to confidently assert that sunspots dominate CO2?

Rasmus Benestad has a new article on the Encyclopedia of Earth website examining these claims in a cool, professional style. He finds them wanting, though those not used to reading the primary literature will not immediately grasp how severely wanting. The article is nicely summarized by this image, which compares solar activity (red, pale blue, grey), CO2( green), and observed global temperature (dark blue) over the past 6 solar cycles.

Anyone claiming that sunspots dominate CO2 in the contemporary record has got a whole lot of ‘splainin’ to do. Of course, with enough knobs on your theory you can explain anything. It is interesting to note how quick the skeptics, er, denialists, er, cosmoclimatologists are to reduce the dimension of the problem (to a global temperature trace). Which is why I prefer to call the problem “global climate change” and not “global warming”. If you reduce everything to a scalar it’s a lot easier to come up with theories. (All of which leads to my point about the best theory being the one with the fewest knobs; more on that to follow in a later post.)

Even so, as you can see, there’s not just a little bit of weaseling needed to actually make a case out of the sunspots as the “culprit” in the global warming that is not happening and is good for you.