Sea levels 'could be rising a centimetre a year' by 2100, say scientists

Study authors hail 'game-changing' revelation

Giant tabular icebergs surrounded by ice floe drift in Vincennes Bay in the Australian Antarctic Territory (REUTERS)

Earth’s sea level could be rising by a centimetre per year by the end of the century, scientists believe.

The rate of the oceans’ rise is increasing by about 0.08mm every year – not remaining constant at the 3mm per year previously observed by satellites, researchers said after analysing 25 years-worth of satellite data.

It means the total rise between 1993 and 2100 could be 65cm, according to Steve Nerem of the University of Colorado. At the turn of the next century the rate of rise could be 10mm a year or more, the university said.

He 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.

“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.”

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. Countries with large low-lying areas like Bangladesh would also be endangered.

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 either by warmer water expanding, or through the flow of melting land ice into the oceans.

Dr Nerem’s team included members from the University of South Florida, the National Centre for Atmospheric Research, Old Dominion University and Nasa‘s Goddard Space Flight Centre.

They interrogated satellite measurements logged from 1993 onward, taking account of events like volcanic eruptions and El Niño that can cause fluctuations in the mean sea level.

Those were cross-checked with tide gauges. The findings, which predict a total sea level rise of between 53cm and 77cm by 2100, are published in Proceedings of the National Academy of Sciences.

The researchers wrote that satellite altimetry had previously shown global mean sea level to have risen at a rate of about 3mm a year since 1993.

“Using the altimeter record coupled with careful consideration of inter-annual and decadal variability as well as potential instrument errors, we show that this rate is accelerating” at about 0.08mm a year, ”which agrees well with climate model projections”, they said.

Co-author Gary Mitchum, of Florida’s College of Marine Science, said: “The acceleration predicted by the models has now been detected directly from the observations. 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.”

Additional reporting by agencies