manchester climate monthly

MCFly reader (and artist!) Jane Lawson (see video here) reviews a book that has been four billion years in the making.

The cosily-named Goldilocks Planet is a review of 4 billion years of the Earth’s climate history written by Jan Zalasiewicz and Mark Williams, two geologists at the University of Leicester. It covers evidence going back to the Hadean Eon, as Earth re-stabilised following the collision with Theia that set up the basic machinery that regulates Earth’s climate, defining the spin and tilt of Earth and setting up the Earth-Moon system which controls day-night cycles and seasons. Zalasiewicz and Williams take us through the following four billion years, through the warm Archaean era, the evolution of simple life, the Earth’s first glaciation around 3 billion years ago, the establishment of an oxygen-bearing atmosphere around 2.4bn years ago, the more than a billion years of relative stability before the next major glaciation, the invention of sex about 1bn years ago (so Philip Larkin was way out), the more frequent but less extreme glaciations of the Phanerozoic Era, the appearance of modern animal groups around half a billion years ago, through a couple of hyperthermals and on into the last Ice Age, the Holocene and now the Anthropocene.

The book describes the many different types of evidence – ocean sediments, ice cores, fossilised tooth enamel and the like, summarises the different interpretations put on this evidence and introduces many significant figures from the investigation of Earth’s climate, often with names that have become part of the geographical/geological record, such as Louis Agassiz and Carl Larsen. A lay reader such as myself will find out a lot about silicate weathering (a major mechanism for removing carbon dioxide from the atmosphere), the disposition of land masses, different aspects of the Milankovitch cycles, and their effects on climate. Zalasiewicz and Williams are scrupulous in pointing out the degrees of uncertainty in drawing conclusions about ancient, and comparatively recent, climate events but build a coherent picture of periodic releases and reabsorptions of carbon and fluctuations in temperature, bringing us to the comparatively stable period we inhabited until very recently, the Holocene/Anthropocene.

At times their reluctance to be definite is frustrating – referring to the current warming, they say “it is highly likely – much more likely than not – that the temperature trend is anthropogenic.” Would it really have been a departure from scientific rigour to have said “almost certainly”? “Highly likely”, in the face of what we are seeing, seems the kind of language that allows denialists to say “well even the scientists aren’t definite about it.” Later on, eight pages after giving the information that 2012 is the 34^th consecutive year hotter than the twentieth century average and that average annual temperatures on the Antarctica Peninsula have risen by nearly 3 °Celsius in the last fifty years, they write that they consider it “very likely that climate has already started to change towards greater global warmth”. You don’t say!

In their defence, they are used to dealing with immense geological timescales, where fifty years is not even the blink of an eye, or even the passage of a nerve impulse across a single synapse. But elsewhere they make the point that our intervention is unique in geological terms; rather than releasing two to four trillion tons of carbon over tens of millennia, as calculated for the Toarcian and Paleocene /Eocene hyperthermals, we have released half a trillion tons in just a couple of hundred years.

The last time carbon dioxide levels were this high was three million years ago in the Pliocene, when sea levels were ten to twenty metres higher than today and large ice masses in West Antarctica grew and collapsed repeatedly. Average global surface temperature was warmer than today by about 3° C – in the range predicted for the late 21^st century. The long-term forecasts given by the authors are even less cheery; for any readers with children, in your children’s lifetimes sea levels will exceed levels not seen since before Antarctica ice sheet started growing, some 33 million years ago.

So how useful is this book in helping us respond to the situation in which we find ourselves? There are two perspectives in this book that I haven’t come across that often. The first was the emphasis on the oceans; even if the authors still admit to some possibility of uncertainty about whether the world is warming and whether that warming is anthropogenic, they admit to none about the increasing acidification of the ocean and its consequences – the killing off of the coral reefs and most carbonate-shelled plankton, with the attendant consequences on the rest of the ecosystem and the impoverishment of the seas.

And the second is the emphasis on the relative stability of the Holocene, as compared to other interglacial periods. The climate, especially over the last half a million years, has been particularly febrile, changing every few thousand years, often abruptly. If such a change happens now, after we have settled most of the globe, especially the low-lying areas that became available once sea level had stabilised around 5,000 years ago, it will be, to understate, very disruptive of human society: “The Earth climate system is clearly in a long-term state in which it can turn on a sixpence…and react strongly and quickly to relatively modest stimuli.” Or, in the words of the oceanographer Wallace Broecker: “climate is an angry beast” and we are currently poking it with a stick.

Finally, they make the welcome point that the cutting of emissions is unlikely to “damage” the economy to anything like the extent that the global banking crisis did, or to cost as much as a couple of medium-sized wars on foreign soil.

Where does this leave us? Who will find this book fruitful? It is not a page-turner of the order of, say, Jared Diamond’s Guns Germs and Steel, or Bill Bryson’s A Short History of Nearly Everything. It is quite dry and at times the chronology isn’t quite as clear as it might be. It’s a great resource for those, like me, who enjoy accumulating information and building up a picture of large-scale processes. There are some juicy nuggets, such as the fact that in the last Ice Age, ice sheets covered north London but not south London, or that it was Goethe who coined the term “Ice Age”. For anyone who is still undecided about whether a temperature rise beyond two degrees is a Bad Thing, there is plenty on what a return to Pliocene conditions is likely to involve. Although the level of caution about stating that anthropogenic warming is happening takes me aback, and I can only wonder about the pressures on scientists that make them favour phrases like ‘highly likely’, the authors clearly do intend it as a clarion call to action, on the behalf of the oceans if nothing else. For anyone wanting to back up discussions of current trends with an in-depth knowledge of previous climatic behaviour, it’s extremely useful. These are first and foremost scientists not writers , and it does show, but the book builds a fascinating picture of Earth’s climate over the past four billion years and the many factors that have gone to shape it.

http://www.janelawson.co.uk/

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