The global cooling myth

Every now and again, the myth that “we shouldn’t believe global warming predictions now, because in the 1970′s they were predicting an ice age and/or cooling” surfaces. Recently, George Will mentioned it in his column (see Will-full ignorance) and the egregious Crichton manages to say “in the 1970′s all the climate scientists believed an ice age was coming” (see Michael Crichton’s State of Confusion ). You can find it in various other places too [here, mildly here, etc]. But its not an argument used by respectable and knowledgeable skeptics, because it crumbles under analysis. That doesn’t stop it repeatedly cropping up in newsgroups though.

I should clarify that I’m talking about predictions in the scientific press. There were some regrettable things published in the popular press (e.g. Newsweek; though National Geographic did better). But we’re only responsible for the scientific press. If you want to look at an analysis of various papers that mention the subject, then try http://www.wmconnolley.org.uk/sci/iceage/.

Where does the myth come from? Naturally enough, there is a kernel of truth behind it all. Firstly, there was a trend of cooling from the 40′s to the 70′s (although that needs to be qualified, as hemispheric or global temperature datasets were only just beginning to be assembled then). But people were well aware that extrapolating such a short trend was a mistake (Mason, 1976) . Secondly, it was becoming clear that ice ages followed a regular pattern and that interglacials (such as we are now in) were much shorter that the full glacial periods in between. Somehow this seems to have morphed (perhaps more in the popular mind than elsewhere) into the idea that the next ice age was predicatable and imminent. Thirdly, there were concerns about the relative magnitudes of aerosol forcing (cooling) and CO2 forcing (warming), although this latter strand seems to have been short lived.

The state of the science at the time (say, the mid 1970′s), based on reading the papers is, in summary: “…we do not have a good quantitative understanding of our climate machine and what determines its course. Without the fundamental understanding, it does not seem possible to predict climate…” (which is taken directly from NAS, 1975). In a bit more detail, people were aware of various forcing mechanisms – the ice age cycle; CO2 warming; aerosol cooling – but didn’t know which would be dominant in the near future. By the end of the 1970′s, though, it had become clear that CO2 warming would probably be dominant; that conclusion has subsequently strengthened.

George Will asserts that Science magazine (Dec. 10, 1976) warned about “extensive Northern Hemisphere glaciation.”. The quote is from Hays et al. But the quote is taken grossly out of context. Here, in full, is the small section dealing with prediction:

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