Once a Cinderella, earth sciences are now the most exciting and vital studies on the planet. Waking the Giant is a major contribution. In the first part, it details the salient aspects of the earth’s climatic history to establish the current state of global warming. But the crucial aspect of the book is the thesis that climate change and volcanic activity are linked.
At first surprising and unlikely, this idea becomes blindingly obvious when you understand the movement of the earth’s crust under the weight of almost 2 miles of ice and then its partial removal. Some facts about this are well known. When the polar ice sheet contracted at the end of the last Ice Age, Scandinavia began a rise of perhaps 1000 ft. This process is still going on, one consequence of which is that Britain is being flipped about its axis, Scotland rising and southeast England sinking at the rate of about 1 mm per year.
The quest to understand the links between the air, the oceans, and the rocks has produced some remarkable correlations. GPS techniques have shown that the movement of water and ice around the world through the seasons causes the earth to bulge slightly on an annual cycle. In the Northern Hemisphere winter it contracts by 3 mm whilst the Southern Hemisphere expands and vice versa in the summer.
McGuire looks at many possible triggers for the incidence of volcanic eruptions and earthquakes. The most important one is that rebound after ice has melted. Volcanoes and faultlines are in a precarious state of equilibrium. A shift caused by rebound after ice is just the kind of mechanism to tip them into activity. The geological record shows that there was an increase in volcanic activity during the most intensive period of deglaciation from 12,000 to 5000 years ago.
Waking the Giant describes some of the major episodes and their consequences for human life, the most terrifying in recent history being the 1783 and 1815 eruptions of the Grímsvötn volcano in Iceland and the Tambora volcano on Java, respectively which blighted harvests in Europe for several years after. But these pale into insignificance compared to the giant Sumatran Toba volcano of 74,000 years ago. It was so large its signature in terms of ash deposited in the geological record is unmissable. It is thought to have come close to wiping out the human race. Even worse was the geologic catastrophe of 252 million years ago that destroyed 95% of living species – the greatest extinction on record. This is now thought to have been caused by a massive eruption of magma plates in Siberia: the Siberian Traps.
The geological processes that caused the Siberian Traps and the Toba eruption are still active. In particular, the possibility that global warming will release the vast store of frozen methane hydrates could produce mayhem on a major scale.
We have been lulled into complacency by the fact that human civilisation developed against the only possible backdrop – an extended period of benign climate. It’s the only world we have known. But it’s not the only world we are going to get.