The Goldilocks Planet: The Four Billion Year Story of Earth's Climate

七月 19, 2012

Summarising 4 billion years of Earth's climate history for a general readership is no mean feat and the authors of this book, two geologists at the University of Leicester, have achieved it very well overall. Jan Zalasiewicz and Mark Williams take us on a long climatic journey from the early Hell-like conditions during the Hadean and Archean aeons, when Earth's atmosphere was dominated by methane and ammonia, to the earliest (rare) glaciations of 2.8 and 2.4 billion years ago that broadly marked the transition into the Proterozoic with the attendant (some say linked) rise of an early bacteria-oxygenated atmosphere 2.2 billion years ago. This was followed by the extensive glaciations after 750 million years ago that some say covered the entire planet ("Snowball Earth") and, shortly thereafter, the first appearance of complex multicellular life forms around 600 million years ago (known as the "Cambrian explosion", although new data suggest more of a slow fizzle).

The past 600 million years of the Phanerozoic aeon have seen broad swings in global climate from "ice house" to "greenhouse" conditions; the last ice house broadly began some 65 million years ago (with the first ice forming over Antarctica about 40 million years ago) and we are still in it, the last Ice Age having ended only 10,000 years ago. The role of extraterrestrial "astronomical" forces in dictating the timing of glaciations over the past 2.5 million years (the Quaternary) is well told here. The authors' narrative is engaging and wafts the reader along from one event to another.

On the whole, this is a balanced, well-written, mostly comprehensive and well-argued book. As a long-term university lecturer and researcher of ancient glacial climates, I would certainly recommend it to the wider non-academic public and also to students as a "dipper" before embarking on their own journeys through the maze that is the journal literature. It is a very easy read and additional cited references point to more exhaustive treatments of select topics elsewhere.

There are, however, a couple of negatives. First, the illustrations are a disappointment: black and white, few in number and surprisingly uninformative as to what precisely ancient palaeotemperatures were. Second, the climate of the most recent past is only fleetingly treated. The Holocene (the past 10,000 years since the most recent Ice Age) is "a climate plateau", according to the authors, one of the most stable phases of climate of the past 400,000 years. But there is little mention of the Hypsithermal (the Holocene's warmest period), the Neoglacial (the subsequent cooling period) and the various shorter phases of warming and cooling that have so greatly influenced the evolution of human societies (eg, the Little Ice Age). The temperature changes from one to another may not have been great, but the effects were profound globally. To my mind, William Ruddiman's 2005 book Plows, Plagues, and Petroleum: How Humans Took Control of Climate, which the authors do not cite, is a better guide to the Holocene and the interplay of human activity and climate. Moreover, what of the role of climate change in the appearance of our species about 2.5 million years ago, and our subsequent evolution and eventual migration out of Africa? These gaps are missed opportunities to underscore the central importance of climate change.

At the end of the book, the authors sensibly steer well clear of any hand-wringing or preaching about "what should we do about climate change", and instead present published predictions about our climatic future. These are many and varied, and often directly opposed, underscoring the sheer uncertainty of the science. This lack of agreement isn't a position of weakness and doesn't reflect the failure of scientists - or, those leaked University of East Anglia emails to the contrary, the scientific method - to get to grips with the problem. It is a statement of fact; a challenge to politicians not to make knee-jerk reactions; and an invitation to future generations to get involved and make a career in the still-emerging field of global change science.

The Goldilocks Planet: The Four Billion Year Story of Earth's Climate

By Jan Zalasiewicz and Mark Williams. Oxford University Press. 336pp, £16.99. ISBN 9780199593576. Published 26 April 2012



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