Britain will spend billions to defend against rising tides over the coming decades, but experts are sharply divided as to how far and fast the waters will rise, reveals Roger Highfield
An apocalyptic vision of a deluged Britain is one of the most potent, chilling and seductive images to emerge from the debate about climate change. All at sea: A 60-metre rise in sea levels could leave the Houses of Parliament semi-submerged, and would fundamentally redraw the map of Britain.
The power of such pictures helps account for the success of Al Gore’s Oscar-winning environmental documentary, An Inconvenient Truth; its warnings over rising sea levels helped win the former US Vice-President a Nobel Prize.
But just before Gore shared the prize for raising global awareness of climate change, a High Court judge ruled that the film contained errors, not least an “alarmist” assertion that the sea would rise up to 20ft “in the near future” as the ice in Greenland or Western Antarctica melts.
He pointed out that scientists believed that the ice would take millennia to melt: “The Armageddon scenario [Mr Gore] predicts, insofar as it suggests that sea level rises of seven metres might occur in the immediate future, is not in line with the scientific consensus.”
But as the Intergovernmental Panel on Climate Change (IPCC), which shared the Nobel with Gore, prepares to deliver its latest report next week, the truth is that there is no such scientific consensus at all.
While scientists agree that sea levels rose by six inches over the course of the 20th century, Professor David Vaughan of the British Antarctic Survey admits that estimates of future rises remain alarmingly hazy.
A Doomsday scenario, such as our map of Britain after a 60m rise in sea levels (inset), is highly unlikely - it would involve the bulk of the planet’s ice melting. But a rise of just a metre or more would wipe out the Norfolk Broads and the Wash, boosting the risk of devastating storm surges.
“With around 17 million people living near the coast in the UK, this is something we cannot afford to ignore,” says Prof Vaughan. One financial disaster zone would be the Thames Estuary, in which 1.25 million people live, 1.5 million commute and there are assets worth up to £100 billion.
In some areas, insurance cover might be withdrawn, leading to the collapse of the property market. The Environment Agency’s “Thames 2100” project, so named because it aims to protect the capital for the rest of this century, is intended to upgrade London’s defences by 2030.
This alone could cost around £20 billion – and Prof Vaughan warns that because billions more could be spent on coastal defences over the coming decades, we must have a better understanding of how to use this money efficiently and wisely, with a minimum of alarmist hysteria.
Later this month, in the Natural History Museum’s annual science lecture, Prof Vaughan will explain how the IPCC, the pre-eminent body engaged in crystal-ball gazing, cannot make firm predictions about sea-level rises - because scientists remain in the dark about how the Earth’s ice will behave, despite the efforts of 2,500 experts in more than 130 countries, including Prof Vaughan himself.
Understanding the effects of vanishing ice sheets “is the number one priority in the coming decade”, he insists. These experts are not concerned about sea ice: just as the level of a gin and tonic remains unchanged as the ice cubes in it melt, so the fate of sea ice is mostly irrelevant to sea levels.
It is land ice that is the problem: if it all melted, sea levels would rise a staggering 70m. Fortunately, 57 of those metres are locked up in Eastern Antarctica, which has been stable for 20 million years and looks likely to cope with global warming.
But there are bodies of land-borne ice that give cause for concern in Greenland and Western Antarctica, which could contribute up to seven and five metres respectively. Prof Vaughan’s research focuses on the ice sheet cloaking 99 per cent of Antarctica, the coldest, windiest and most remote spot on Earth, which holds 70 per cent of the planet’s fresh water.
Previously, it was thought that the 6,500ft-thick blanket was gaining more ice than it was losing. In recent years, however, sophisticated satellite measurements have revealed that the West Antarctic ice sheet, which is some eight times smaller than that in the east, is thinning over an area the size of Texas.
The ice lost, up to two metres a year, is enough to add 0.4mm annually to sea levels, though it is hard to say whether this is part of the natural life cycle of the continent. That is also why experts remain sceptical when Green groups join the dots between TV footage of vast icebergs “calving” and global warming; icebergs are launched every decade or so as glaciers - great rivers of ice - slide into the ocean.
Even so, Prof Vaughan is worried. The flow of Pine Island Glacier, the largest in the west of the continent, has accelerated over the past 15 years. The picture is equally bleak when it comes to Greenland, which has seen “decades of rapid warming”.
Over 30 years, the extent of Arctic sea ice has shrunk by 2.7 per cent per decade. Some models predict an Arctic free of sea ice in summer by 2100. But the reason for the controversy, and the row over Gore’s claims, is that there are many uncertainties, mostly arising from the lack of data on what ice sheets did in the past.
In particular, there are insufficient long-term satellite data to unpick the effects of natural climate change from that caused by man. To add to the muddle, temperatures in Greenland do not seem to exceed those seen during a warm period in the 1930s.
Antarctica shows no evidence of overall warming, though its peninsula, which extends towards South America, has recently grown hotter five times more rapidly than the rest of the world, warming by almost 3ºC over 60 years.
In fact, the effects of warming on Antarctica are still not understood. Higher temperatures increase atmospheric water content and the rate of snowfall that feeds the glaciers. How much more quickly this will enable glaciers to slip into the seas (their top speed is currently around six miles a year) is hard to say, because these rivers of ice run on an abrasive mix of rubble and rocks that bulldoze the underlying geological record, erasing traces that could help link temperature and melting.
There are also “second order effects”. The most important concerns the way the warming oceans expand, just as a railway track stretches in sunshine. This could add inches to sea levels.
Another depends on the gravitational tug of the ice itself: the great lump of Antarctic ice exerts a pull on nearby waters, so that when it melts, and its gravity lessens, this piled-up water ripples back worldwide.
Current climate forecasting focuses on the atmosphere, when it is the warmth of neighbouring oceans, and the way they circulate, that has the biggest effects on the Antarctic ice. Scientists know that they do not know how these factors work together, because current predictions underestimate changes seen in both Greenland and Antarctica.
All this confusion, and the multiplicity of factors to take into account, helps explain why the topic is so strongly argued over. Prof Vaughan says the main message is not to panic – the effects of melting will be gradual, in the order of three metres per century if the evidence of the past 20,000 years is anything to go by.
But even then, the costs of holding back the flood could be huge. That is why, as Prof Vaughan insists, “scientists need to nail down their predictions of sea level rise pretty quickly”.
The Natural History Museum’s Annual Science Lecture is a leading forum for scientific debate. Prof David Vaughan will deliver 'Flood Warning? The Global Impact of the Melting Ice Sheets’ on Tuesday, November 27, at 7.30pm. Admission: £12, concessions and members £9, students £6. Call 020 7942 5555 or see
http://www.nhm.ac.uk/visit-us/whats-on/special-events/annual-science-lecture/. See the impact of rising sea levels at
http://flood.firetree.net/
