Sea levels are increasing at an accelerating rate that could see them rising by a whole centimetre per year by 2100, research has shown.
The end-of-century surge rate would put many low-lying regions of the world at risk of flooding, including major coastal cities such as Miami and Shanghai.
Scientists analysing 25 years of satellite data discovered that global sea level is not rising at a steady 3mm per year, as previously thought. Instead, the rate of increase is speeding up, adding an extra 0.08mm with every passing year.
If the trend continues, it is likely to lead to an annual average sea level rise of at least 10mm per year by 2100.
Lead scientist Professor Steve Nerem, from the University of Colorado at Boulder, US, said: “This acceleration, driven mainly by accelerated melting in Greenland and Antarctica, has the potential to double the total sea level rise by 2100 as compared to projections that assume a constant rate, to more than 60cm instead of about 30cm.
“And this is almost certainly a conservative estimate. Our extrapolation assumes that sea level continues to change in the future as it has over the last 25 years. Given the large changes we are seeing in the ice sheets today, that’s not likely.”
Some more pessimistic forecasts have suggested sea level rises of several feet by the end of the century if greenhouse gas emissions continue unabated.
Rising concentrations of carbon dioxide and other greenhouse gases in the atmosphere raise the temperature of air and water.
This can impact on sea levels in two ways, either by warmer water expanding, or through the flow of melting land ice into the oceans.
Thermal expansion is said to have contributed about half of the 7cm of global average sea level seen in the past 25 years.
The new research, published in the journal Proceedings of the National Academy of Sciences, involved an in-depth study of satellite measurements of the height of the Earth’s surface made since 1992.
The scientists checked their results using tidal data and took account of volcanic eruptions and other natural phenomena that can cause sea level to fluctuate.
Co-author Dr Gary Mitchum, from the University of South Florida, US, said: “I think this is a game-changer as far as the climate change discussion goes.
“For example, the Tampa Bay area has been identified as one of 10 most vulnerable areas in the world to sea level rise and the increasing rate of rise is of great concern.”