Some context, by Nigel Calder

These pages are generally reserved for scientific rather than "popular" references. However, Nigel Calder was kind enough to send me the following, so I include it as interesting context.

I should perhaps note that there are elements of the text below that are definitely not my opinions. In particular, the assertion that "the IPCC accepts that a steady Milankovitch cooling is in progress" is dubious: the IPCC accepts (as do we all) that insolation at certain latitudes has been declining, but does not link this to cooling.

In "The Weather Machine" BBC Publications 1974 p. 134 I [Nigel Calder] wrote:

"Going by past form, the warm periods between ice ages last about 10,000 years and ours has lasted 10,000 years. One might therefore argue that there is a virtual certainty of the next ice age starting some time in the next two thousand years. Then the odds are only about 20 to 1 against it beginning in the next 100 years."

I would not change a word of this, 25 years on. It arose partly from the first formal confirmation of the Milankovitch effect (which I published in Nature) and partly from testimony by leading climate experts of the day. George Kukla of Cornell/Lamont said in the TV version of The Weather Machine:

"... And the warm periods are much shorter than we believed originally. They are something around 10,000 years long, and I'm sorry to say that the one we are living in now has just passed its 10,000-year birthday. That of course means that the ice age is due now any time."

There was also a shift in ideas about how ice ages started, with Hubert Lamb and Alastair Woodroffe (1970) arguing that ice sheets grew from the bottom up rather than spreading slowly as glaciers from a mountainous centre. I called this concept the "snowblitz" because of the sudden chilling of huge areas by unmelted snow which it implied. It gave a sharper meaning to the idea of the onset of an ice age.

By the way, the IPCC accepts that a steady Milankovitch cooling is in progress, as part of its otherwise rather selective climatological background for discussing current fluctuations. And Milankovitch is nowadays used to date the comings and goings of the ice more reliably than sedimentation rates do -- something I suggested in my Nature paper.

I've just found an offprint of a Royal Institution lecture "Shall We Fry or Freeze?" where I said:

"The chances of a drastic cooling occurring in our lifetime are small - a good deal less, no doubt, than the risk of the man-made disaster of nuclear war - but the risk is not zero ..."

I don't have the year or volume number of their publication, but the page number is p. 253. I think it was 1980 or 81, something like that.

More amusingly on RI p. 254 I noted the wide awareness of the new climatology at that time:

"A New Yorker cartoon depicts the typical grouchy New York drinking man saying to the typical patient bar-tender, 'And what did we *do* with our ten-thousand-year warm spell between ice ages? Nothing.'"