Source: The Guardian
Author Bill McGuire
Article published Tue 7 Aug 2007 15.45
Never mind higher temperatures, climate change has a few nastier surprises in store. Bill McGuire says we can also expect more earthquakes, volcanoes, landslides and tsunamis
Unlike most apparently intractable problems, which have a tendency to go away when examined closely and analytically, the climate change predicament just seems to get bigger and scarier the more we learn about it.
Now we discover that not only are the oceans and the atmosphere conspiring against us, bringing baking temperatures, more powerful storms, floods and ever-climbing sea levels, but the crust beneath our feet seems likely to join in too.
Looking back to other periods in our planet's history when the climate was swinging about wildly, most notably during the last ice age, it appears that far more than the weather was affected. The solid earth also became restless, with an increase in volcanic activity, earthquakes, giant submarine landslides and tsunamis. At the rate climate change is accelerating, there is every prospect that we will see a similar response from the planet, heralding not just a warmer future but also a fiery one.
Several times in the past couple of million years the ice left its polar fastnesses
and headed towards the equator, covering much of the world's continents in ice sheets over a kilometre thick, and sucking water from the oceans in order to do so. As a consequence, at times when the ice was most dominant, global sea levels were as much as 130m lower than they are today; sufficient to expose land bridges between the UK and the continent and Alaska and Russia.
Each time the ice retreated, sea levels shot up again, sometimes at rates as high as several metres a century. In the mid 1990s, as part of a study funded by the European Union, we discovered that in the Mediterranean region there was a close correlation between how quickly sea levels went up and down during the last ice age and the level of explosive activity at volcanoes in Italy and Greece.
The link was most obvious following the retreat of the glaciers around 18,000 years ago, after which sea levels jumped back up to where they are today, triggering a 300% increase in explosive volcanic activity in the Mediterranean in doing so. Further evidence for a flurry of volcanic action at this time comes from cores extracted from deep within the Greenland ice sheet, which yield increased numbers of volcanic dust and sulphate layers from eruptions across the northern hemisphere, if not the entire planet.
But how can rising sea levels cause volcanoes to erupt? The answer lies in the enormous mass of the water pouring into the ocean basins from the retreating ice sheets. The addition of over a hundred metres depth of water to the continental margins and marine island chains, where over 60% of the world's active volcanoes reside, seems to be sufficient to load and bend the underlying crust.
This in turn squeezes out any magma that happens to be hanging around waiting for an excuse to erupt. It may well be that a much smaller rise can trigger an eruption if a volcano is critically poised and ready to blow.
Eruptions of Pavlof volcano in Alaska, for example, tend to occur during the winter months when, for meteorological reasons, the regional sea level is barely 30cm (12in) higher than during the summer. If other volcanic systems are similarly sensitive then we could be faced with an escalating burst of volcanic activity as anthropogenic climate change drives sea levels ever upwards.
Notwithstanding the recent prediction by the Intergovernmental Panel on Climate Change (IPCC) that sea levels in 2100 will be a measly 18-59cm (7-23in) higher, Jim Hansen – eminent climate scientist and director of NASA's Goddard Institute for Space Studies – warns that we could see a one to two metre rise this century and several more in the next. Other climate scientists too, forecast substantially greater rises than the IPCC, whose prediction excludes any consideration of future changes in polar ice sheet behaviour. A worst-case scenario could see a return to conditions that prevailed around 14,000 years ago, when sea levels rose 13.5 metres (44ft) - the height of a three-storey house - in the space of about 300 years.
Such a dramatic rise in coming centuries would clearly spell catastrophe for our civilisation, with low-lying regions across the planet vanishing rapidly beneath the waves. Just a one metre (3.28ft) rise would threaten one third of the world's agricultural land, two metres (6.56ft) would make the Thames flood barrier redundant and four metres (13.12ft) would drown the city of Miami, leaving it 37 miles (60km) off the US coast.
As sea levels climb higher so a response from the world's volcanoes becomes ever more likely, and perhaps not just from volcanoes. Loading of the continental margins could activate faults, triggering increased numbers of earthquakes, which in turn could spawn giant submarine landslides. Such a scenario is believed to account for the gigantic Storegga Slide, which sloughed off the Norwegian coast around 8,000 years ago, sending a tsunami more than 20 metres (66ft) high in places across the Shetland Isles and onto the east coast of Scotland. Should Greenland be released from its icy carapace, the underlying crust will start to bob back up, causing earthquakes well capable of shaking off the huge piles of glacial sediment that have accumulated around its margins and sending tsunamis across the North Atlantic.
The Earth is responding as a single, integrated system to climate change driven by human activities. Global warming is not just a matter of warmer weather, more floods or stronger hurricanes, but is also a wake-up call to Terra Firma. It may be no coincidence that one outcome of increased volcanic activity is likely to be a period of falling temperatures, as a veil of volcanic dust and gas reduces the amount of solar radiation reaching the surface. Maybe the Earth is trying to tell us something. It really would be worth listening before it is too late.
Bill McGuire is the director of the Benfield UCL Hazard Research Centre. His book Surviving Armageddon: Solutions For a Threatened Planet is published by OUP. His next book, What Everyone Should Know About the Future of Our Planet: And What We Can Do About It, is published by Orion in January next year.
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