MY Review of Books

I’ve finally got round to reading a number of the many climate change-related books that have been published in recent months. These books seem to have caught the public imagination in ways that are different than in the past, and so it’s worth examining how they do. The three I’ve read are; Eugene Linden’s The Winds of Change, Elizabeth Kolbert’s Field Notes from a Catastrophe and Tim Flannery’s The Weather Makers. The first two writers are journalists, while the third is a scientist by background, and while there is some overlap in contents all of them, they are clearly distinct works in quite different styles. I’ll mostly stick to commenting on the science though…

Eugene Linden’s book is very well written and sets up the book as a prosecutorial case that climate change can have (and has had) serious impacts on human society. He picks out a number of purported climate changes – the 8.2 kyr event, two less well-defined changes around 5200 and 4200 years ago, a mysterious (volcanic?) event in 536 AD, the Mayan collapse around 800 AD, and the Norse colony collapse in Greenland to make his case that societies can be vulnerable to abrupt shifts in rainfall, temperature etc. The 8.2 kyr event qualifies as an abrupt change by almost any definition (except that adopted by the NRC panel on the subject curiously) and was most likely tied to the catastrophic final draining of paleo-lake Agassiz and subsequent changes in the North Atlantic ocean circulation (see a summary of some of our recent research on the topic). This mechanism is not relevant to the other highlighted changes, and unfortunately no well supported ’causes’ have yet been demonstrated for the events in 5200 and 4200 BP. Solar forcing has been suggested for the Mayans and for the Little Ice Age, but hard evidence is difficult to come by.

Societal impacts linked to the 8.2kyr event involve potential changes in the Natufian culture in the Levant, but while intriguing, the imprecision of dating and lack of written evidence mean that this link remains speculative. However, evidence for societal impacts are tied to drought on ancient civilisations is much stronger – the ancient ‘Curse of Akkad’ describing the droughts affecting the Akkadian Empire; the Mayan collapse etc. – and this is well brought out in the text.

One example that I wasn’t previously aware of, were the climate events of 536 AD – ‘dry fogs’, crop failures, ‘dim suns’ and yellow snow etc. – features consistent with a large volcanic eruption, possibly near the site of Krakatoa – and which correlates with evidence of a sulphate peak in the North GRIP ice core at the same time. Linden quotes David Keyes as suggesting that the societal impacts of this event included the plague and the onset of the European ‘Dark Ages’. You don’t necessarily need to buy into this to get a sense of how disruptive this event was though.

Linden talks to the right people and makes a strong case, but I think he errs in seeing all of the climate changes as being analogous. The effects of circulation change in the North Atlantic are different to (potentially solar-driven) rainfall variability in the sub-tropics and are different again from the impacts of changing frequency and intensity in El Nino patterns. He unfortunately makes a large over-estimate in describing the magnitude of the 8.2 kyr event (claiming it lead to 5 deg C of global cooling, instead of a local result for Greenland), and then compares other ‘events’ to this more (climatically) well-documented case. There are a few more minor errors – isotopes are denoted by a pre-subscript (18O) instead of a superscript (18O) but we can probably blame the copy-editor for that. Linden appears to take seriously a suggestion that the Mayans were aware of multi-decadal variations in the sun’s irradiance and built them into their calendar – something that seems extremely unlikely to me. Overall though, the evidence for serious climatic impacts on societies is pretty strong and he swayed this member of the jury.

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