Sea level change not all about us

There are a variety of reasons why sea levels are changing - and scientists arguing the case for man-made climate change must find reliable ways to predict natural variations if they are to paint an accurate picture of our own influence.

This was the premise of an event hosted by the Geological Society in London this week, where scientists from around the world specialising in a variety of disciplines gathered to discuss sea level changes over the millennia – and more recent shifts attributable to human activity.

Delegates heard how accurate mapping of changes ten or even twenty thousand years ago are relevant to the rising sea levels we face today, as a better understanding of the past allows us to make predictions of future trends with increased certainty.

But perhaps most interesting for those without an in-depth knowledge of the science behind sea levels were the myriad factors having an impact that are well beyond the control of mankind.

Among these are the sheer weight of the water and the effect that has on the sea beds below it. As the pressure distorts the ocean floor, so the levels of the surface shift – just like if you changed the shape of the bottom of a bowl of water, you would expect to see a change to where the surface lay.

The melting ice caps are also change the volume of the oceans, of course, but even if volumes remain unchanged, regional sea levels can shift as water is moved around the oceans by persistent winds and currents.

“The challenge we face is separating natural processes from the anthropogenic ones,” said Prof Kurt Lambeck, geophysicist and president of the Australian Academy of Science.

“What’s happening today is influenced by what happened 20,000 years ago, [sea levels are] still responding to events that happened some distance in the past.”

Understanding this ‘background noise’ is vital for those wishing to build up a real understanding of modern-day climate change, he said, outlining how this is being done in any number of ways, from lab-based computer modelling to ingenious field work looking at, for example, where Romans built their fish farms and where coral and other sea life had previously flourished but now floundered.

Sam Bond

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