New satellite data shows annual sea level rises are 50 per cent higher than last century, as research suggests one in 10 people could be at risk of coastal flooding by 2100
Sea levels are rising significantly faster than previously thought and are on track to rise by more than 1m by the end of the century, putting entire countries and many of the world's largest coastal cities at risk of inundation.
That is the stark warning from scientists presenting new satellite data and climate models at this week's Climate Congress in Copenhagen, which warns that sea levels have been rising an average of more than 3mm a year since 1993 - an increase of 50 per cent on the average rate of sea level increase during the 20th century.
The most recent study from the Intergovernmental Panel on Climate Change (IPCC) predicted that temperature increases would deliver an increase in sea levels of between 18cm and 59cm by 2100.
But the scientists behind the latest study said that sea level rises were already on track to hit the top end of this projection and if, as expected, rates of sea-level rise increase as temperatures climb, we could see sea levels rise by more than 1m by 2100.
Crucially for business and political leaders making short to medium-term decisions, the research also showed that sea levels could reach 10-20cm above current levels by mid-century, sufficient to pose a significant medium-term threat to many low-lying areas.
Professor Stefan Rahmstorf of the Potsdam Institute for Climate Impact Research explained that at the time the ICC was compiled three years ago, there was not sufficient understanding of dynamic ice loss - the process by which glaciers move into the sea - to account for this contribution to sea level increases.
However, recent research in Greenland and West Antarctica has shown that this process is proceeding far faster than previously thought. The research suggests that Greenland alone is now responsible for rises in sea levels of 1mm a year, while the rate at which glaciers are moving into the sea in areas of the Antarctic is increasing at an "almost exponential" rate.
An increase in sea levels of 1m would affect an estimated 600m people, or 10 per cent of the world's current population, putting them at serious risk of coastal flooding.
Dr Konrad Steffen of the University of Colorado said that delatic regions such as Bangladesh, Myanmar, much of south east Asia and parts of Africa, would be at risk of inundation along with many island nations. Meanwhile, many of the world's largest coastal cities, such as New York, London, Shanghai, Tokyo and Kolkata, would also face huge increases in flood risks.
"You have to remember it is not just the steady increase in sea levels that is the problem, it is that combined with the increased flood risk," warned Dr John Church of the Centre for Australian Weather and Climate Research, adding that research looking at the impact of a 50cm increase in sea levels on areas of the Australian coast found that under such a scenario "flooding events we today expect once in 100 years would occur several times a year".
Rahmstorf also warned that there was a very real danger that a tipping point could be reached this century that would result in sea level rises of many metres. "We need to realise that everything does not just stop in 2100," he said, adding that three million years ago during the pliocene era temperatures were just two to three degrees warmer but sea levels were 25m to 30m higher.
He said that while the relatively slow speed at which continental ice melts meant such huge increases in sea level would not happen for many centuries, there was a risk that once temperatures rise, a process will begin that will result in sea level rises of tens of metres.
The findings should serve as a major wake-up call to political and business leaders.
Previous research from the OECD has suggested that sea level rises would result in the amount of property and assets being at risk of coastal flooding by 2070 increasing tenfold to $35tr (£25tr). But even that figure looks optimistic given the current rate of sea level increase and projected impact of further increases in temperature.
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