70's cooling again: but why?

The good old "1970's cooling" stuff comes up again, this time over at Slate about an article by Chris Mooney. CM blogs about this with "Here We Go Again Over in the "Fray" at Slate, they're having a pointless argument over global "cooling" in response to my recent piece. Will the misinformation ever end?". But in fact, things aren't that bad at all...

Because the comments end up with the right answer: which is to refer to the RealClimate post on the same subject. Excellent.

But re-reading that, and my page http://www.wmconnolley.org.uk/sci/iceage/ I find that one thing is missing, or there only by implication, which is to answer "OK then, so why was there a cooling trend from the 40's to the 70's, if CO2 was increasing?". Which is a fair question. The right answer above answers it about right:

Firstly, the cooling was fairly small, and if it wasn't in the middle of warming periods it probably wouldn't even have been called cooling. The cooling was stronger in the NH (which fits the aerosol explanation), and even there it isn't (in retrospect) nearly as large as some of the datasets of the time seem to have implied.

Secondly, its quite explicable within the standard theory: as usual, its all in the IPCC TAR, specifically SPM and figure 4 and fig 12.7 . Which is to say, its mostly the sulphate aerosols. Those figures can be over interpreted though: as it says elsewhere " These results show that the forcings included are sufficient to explain the observed changes, but do not exclude the possibility that other forcings may also have contributed". Which is to say... that modelling will get better, we may well tighten up these results, and may even discover something unexpected: but its certainly wrong to say the cooling is inexplicable.

1 comment:

John Creighton said...

It is not obvious to me from Michael Mann’s data in MBH98 that NH decreased in the 1970s. Of course I am somewhat skeptical of his data. It appears that temperatures have risen as a result of more CO2 in the atmosphere but I don’t think it is clear if CO2 concentrations or solar flux changes are the greatest contributors to but I think they are somewhat comparable.

Also in question (atleast to me) is if people are the primary contributor of the CO2 concentrations in the atmosphere. I am curious if you know of any accurate measurements of CO2 emissions by the human race. I’d like to do some regression to see if both people and the sun have a significant effect on the CO2 concentrations.