If the title of Matt Ridley’s new book, The Rational Optimist, sounds a little familiar, that’s because it borrows heavily from the world view of one Bjorn “The Skeptical Environmentalist” Lomborg. Both contrarians dismiss global warming as nothing to worry about, although Ridley seems even less convinced that the planet is actually experiencing anthropogenic global warming. I don’t have time to read it — but I did manage to take a look at the kind of thinking that Ridley uses at his blog.
This week, Ridley wrote about what his research in the “Holocene Optimum,” uncovered. What he found, he says, is that it was much warmer about back then than it is today, and:
if the heat of 7,000 years ago, so widespread around the globe and so pronounced in the far north, did not cause planetary catastrophe, why should the lesser warmth of this century?
The problem is Ridley’s version of the mid-Holocene warming is restricted to the Northern Hemisphere. The rest of the planet wasn’t particularly warm at all. In fact, according to a primer on the subject from the U.S. National Climatic Data Center, that warming was a product of changes in the Earth’s orbit which …
… can be easily calculated and predict that the northern hemisphere should have been warmer than today during the mid-Holocene in the summer AND colder in the winter. The paleoclimatic data for the mid-Holocene shows these expected changes, however, there is no evidence to show that the average annual mid-Holocene temperature was warmer than today’s temperatures.
In summary, the mid-Holocene, roughly 6,000 years ago, was generally warmer than today, but only in summer and only in the northern hemisphere. More over, we clearly know the cause of this natural warming, and know without doubt that this proven “astronomical” climate forcing mechanism cannot be responsible for the warming over the last 100 years.
This is not controversial or new. In a 2002 Paleoceanography paper, a pair of Japanese researchers note that there models show that during the mid Holocone “there is about a 0.35°C cooling of the global mean SST [sea surface temperature]” and that “anomaly is in broad agreement with the observed proxy data.”
Here’s how a Wikipedia author sums it up:
In terms of the global average, temperatures were probably colder than present day (depending on estimates of latitude dependence and seasonality in response patterns). While temperatures in the Northern Hemisphere were warmer than average during the summers, the tropics and areas of the Southern Hemisphere were colder than average which comprised an average global temperature still overall lower than present day temperatures.
Also, George Monbiot quickly deals with some of the errors in Ridley’s book.