Tuesday, October 11, 2011

Climatequake: Will global warming rock the planet



FEW things are more likely to prompt instant ridicule from climate sceptics than the idea that there might be a link between global warming and geological disasters such as earthquakes, volcanic eruptions and tsunamis. "Earthquakes are caused by tectonic plate movements - they are not caused by Bubba driving his SUV down the highway," is typical of the responses found in the denialist blogosphere.

Yes, the Earth moves all by itself, but it is becoming increasingly clear that climate plays a role in when and how often. What happens on the surface can suppress quakes and eruptions - and trigger them. There are already signs of such effects in the world's northern regions, which are warming fastest.

So seriously is the issue being taken that an upcoming special report on extreme events and disasters related to climate change, commissioned by the Intergovernmental Panel on Climate Change, will include a section on it. So what exactly is going on and what can we expect during the next century and beyond?

The idea that climate change can affect events such as earthquakes is not as outlandish as it might first seem. While the power of earthquakes comes from the movements of tectonic plates deep beneath the surface, even these stupendously massive structures can be influenced by what is happening at the surface. The rapid erosion of huge quantities of material by the monsoon rains in India, for instance, has affected the motion of the Indian plate over the past few million years.

On a more immediate timescale, there is already plenty of evidence that human activity can trigger earthquakes. The building of vast dams has often been linked to seismic activity, for instance. Some blame the Great Quake of Sichuan in 2008, which killed 80,000 people, on the recently constructed Zipingpu dam just 5 kilometres away from the epicentre.

Mining and drilling activities can also trigger small earthquakes, and at least one geothermal project has been cancelled because of fears of further quakes. And if small geothermal projects can trigger quakes, it is not so surprising that altering the climate of the entire planet will have an effect too.

The crux of the problem is simple: anything that increases or decreases the load on the Earth's crust causes stresses and strains. When this happens slap bang on top of one of the world's many volcanoes or geological faults, where the crust is already under strain, it can make the area more or less likely to erupt or slip. And there is a very heavy substance whose movements depend largely on the weather and the climate: water.

During past ice ages, vast ice sheets several kilometres thick built up over northern Eurasia and north America. The weight of the ice pinned down faults and suppressed the flow of magma. When the ice melted, there was a flurry of earthquakes and volcanic eruptions as faults began to move again.

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