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The world is underestimating the geological consequences of global warming, which could trigger catastrophic earthquakes and tsunamis as the melting of ice sheets reduces the weight on the crust below and unleashes intense seismic activity, a leading earth scientist has warned.
The biggest threat in the north Atlantic comes from the thinning of Greenland’s ice cap, Bill McGuire, professor of earth sciences at University College London, told the British Science Festival in the UK town of Chelmsford on Thursday. Within decades, that could spark huge submarine earthquakes off the coast of Greenland, causing tsunamis with disastrous consequences for North America and probably Europe, he said.
A possible precedent was the “great Storegga tsunami” that devastated the coasts of Scandinavia and the British Isles 8,200 years ago. An offshore earthquake, triggered by the release of pressure after northern Europe’s ice sheets had melted, set off a vast landslide of submarine sediments under the Norwegian Sea. Geological evidence shows the resulting tsunami wave reached 15 to 20 metres high in the Shetland islands and 3 to 6 metres high further down the North Sea.
“As the Greenland ice cap melts, the uplift in the crust is going to trigger earthquakes,” said McGuire. “We don’t know enough about the sediments off the Greenland coast to predict confidently what might happen there, but it is certainly possible that within decades there could be a tsunami right across the north Atlantic.”
Its impact might be comparable to the 2004 Boxing Day tsunami that killed more than 200,000 people around the Indian Ocean, he said.
Greenland has lost 4tn tonnes of ice over the past 20 years through melting and iceberg calving, raising global sea levels by about 1cm, Donald Slater, a glaciologist at Edinburgh university, told the science festival. It will contribute a further 10cm rise this century.
The loss of ice from Greenland and to a lesser extent Iceland and Svalbard is lifting up the earth’s crust around the north Atlantic, McGuire said. Sensitive GPS instruments on coasts around the ocean are beginning to detect this uplift, which is taking place at a rate ranging from a few millimetres to 2.5cm a year.
“The whole central part of Greenland is below sea level, forced down by the weight of the 3km thick ice cover, so the crust has a long way to bounce back,” he said.
On the other side of the Arctic, Alaska — the most seismically active part of North America — is already experiencing more frequent earthquakes. On July 28 a magnitude 8.2 quake, the strongest in the US for 50 years, occurred just off the coast of south-west Alaska.
“When it comes to the geological impact of climate change, Alaska can be seen as the canary in the coal mine,” said McGuire.
He denied being alarmist. “When global temperatures may be rising at the fastest rate in the history of our planet, I’m proud to be raising the alarm,” he said. “Almost every forecast so far about climate change has been an underestimate.”
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