Waking the Giant

By Bryan Walker 18/07/2012

It’s only if we fail to grasp the enormity of the threatened impacts of climate change on the global environment that we can scoff at the notion that even volcanic eruptions and earthquakes may be triggered as a consequence of our continuing to burn fossil fuels. Not that it’s an easy consequence to appreciate, but vulcanologist Bill McGuire’s latest book Waking the Giant: How a Changing Climate Triggers Earthquakes, Tsunamis, and Volcanoes explains it with patient clarity. His book is a fascinating read in its discussion of the past and an alarming one in its analysis of future likelihoods.

The book begins with a straightforward and sobering view of the catastrophe which looms if we continue to fail to act on emissions. The signs of climate change are everywhere apparent and the prospects for the future are bleak. McGuire acknowledges the difficulties of precise prediction of what that future might hold 50 or 100 years from now and suggests that looking back on the past may be the best way to gauge what lies ahead. The main focus of his book is on ways in which Earth’s crust has responded to dramatically changing climates, but he also considers, further back, times of high levels of atmospheric carbon dioxide as possible pointers to what today’s increased greenhouse gases might forebode.

In the latter case he discusses the heat spike, nearly 56 million years ago, of the Palaeocene-Eocene Thermal Maximum (PETM) when the global temperature shot up by 6oC over a 10,000 year time span, with the poles heating by 10oC – 20oC. The cause of this and other warm spikes further back in time seems to have been a sudden rise in the concentration of atmospheric carbon dioxide, and although we have so far in the past two centuries released only one eighth of the amount of carbon that drove the PETM, carrying on with deforestation and the burning of fossil fuel reserves would conceivably bring us close to a similar concentration over a mere fraction of the time.  Continuing as we are could bring a 4oC rise in temperature by 2070.  Coming closer to our own time, McGuire considers the Mid-Miocene Climatic Optimum (MMCO) between 17 and 15 million years ago, which was the last time carbon dioxide levels were higher than they are now, but only in the region of 400-450 ppm which we’re well on the  way to achieving. Mid-latitude temperatures were 3-6oC higher than today. Along with the PETM and the MMCO the third period climatologists find instructive is the much more recent Eemian Interglacial which began a mere 170,000 years ago when global temperatures are estimated to have been 1-2oC higher than today and sea levels 4-6 metres higher. McGuire sees this period as a close analogue for an anthropogenically warmed Earth in the near future.

All of this is not new material, but it is drawn together and explained with compelling clarity and an underlying heartfelt urgency. The choices we make now as to whether we act to slash emissions or not “may decide the fates of millions of species and thousands of human generations”.  It’s a grave responsibility.

In McGuire’s understanding there’s plenty to be concerned about before considering volcanoes and earthquakes, but having made that utterly clear he turns his attention to the geological dimension. The evidence that volcanic eruptions can be triggered by climate change is best found in the rapid climate changes of the ice ages. The sudden switch from an ice world and the enormous changes in the physical environment that involved saw an increase in volcanic activity from two to six times above normal background levels.  McGuire explores the possible reasons for this, which include the removal of ice load, increased precipitation and large changes in global sea levels. The mechanisms are explained and illustrated at satisfying length. Considered en masse the world’s active volcanoes are primed systems sensitive to changes in the hydrological cycle. Past history suggests that the kind of changes expected from anthropogenic global warming will have an effect on volcanic activity.

Moving to consider earthquakes McGuire explains the view that the melting of large ice sheets leads to a combination of spectacular uplift in the lithosphere and increased levels of earthquake activity as tectonic strain beneath and adjacent to the ice sheets is released.  Similarly a relocation of water on a large scale can have loading and unloading effects with the added complication that the pressurisation of pore waters in the rocks adjacent to new or growing reservoirs has been observed to destabilise nearby faults. The new redistribution of water that will accompany the warming of the planet seems bound to cause a response in at least some active faults.

Landslides, including volcano collapse and submarine slides, are next in McGuire’s considerations, with water again playing a key role. His conclusion after a detailed survey of many examples is that we can expect many more incidences of major landslides in a warmer world where water is plentiful, where sea levels are rising, and where the ice that holds together the faces of  mountains is going or gone.

Finally he elaborates on the effects of water relocation, particularly from ice, which the book has already identified as a major factor in the triggering of volcanic or earthquake activity. Here he adds to the localised effects manifested in those phenomena the wholesale change to the planet’s spin characteristics and the pattern of stress and strain in its interior, transmitting the geospheric response widely.

Pulling all this together in a concluding chapter which looks to the future McGuire posits that if we continue with greenhouse gas emissions to the point that we lose the Greenland and West Antarctic ice sheets the resultant surge in sea level is likely to bring a response from the geosphere large enough to be distinguishable from everyday geological activity. The consequences of severe climate change will be disastrous enough without that dimension, but it is a possible addition with which our descendants will have to cope.

Communicating the content of McGuire’s book in broad outline like this doesn’t do justice to the engrossing details with which it is packed, all fully accessible to the general reader and establishing the authority of his discussion. It’s a captivating story, told with due scientific detachment but informed with alarm at the magnitude of the changes we will produce in our world if we insist on burning all the fossil fuels we can find. No one reading the book could say we haven’t been warned.

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