* Seas to rise 16.5 to 69 cm with moderate warming-ice2sea
* Melt of Greenland, Antarctica less severe than expected
By Environment Correspondent Alister Doyle
OSLO, May 14 (Reuters) - A melt of ice on Greenland and Antarctica is likely to be less severe than expected this century, limiting sea level rise to a maximum of 69 cm (27 inches), an international study said on Tuesday.
Even so, such a rise could dramatically change coastal environments in the lifetimes of people born today with ever more severe storm surges and erosion, according to the ice2sea project by 24, mostly European, scientific institutions.
Some scientific studies have projected sea level rise of up to 2 metres by 2100, a figure that U.N. Secretary-General Ban Ki-moon has called a worst case that would swamp large tracts of land from Bangladesh to Florida.
Ice2sea, a four-year project to narrow down uncertainties of how melting ice will pour water into the oceans, found that sea levels would rise by between 16.5 and 69 cm under a scenario of moderate global warming this century.
"This is good news" for those who have feared sharper rises, David Vaughan, of the British Antarctic Survey who led the ice2sea project, told Reuters in a telephone interview.
"But 69 cm is a very real impact ... it changes the frequency of floods significantly," he said. And seas would keep rising for centuries beyond 2100, in a threat to coastal cities and low-lying islands such as the Maldives or Tuvalu.
Ice2sea said a thaw of Antarctica, Greenland and glaciers from the Alps to the Andes would contribute between 3.5 and 36.8 cm to sea level rise this century. The fact that water expands as it warms would add another 13 to 32 cm, Vaughan said.
Some other scientists disputed ice2sea's projections.
"I think the numbers are too low," Dorthe Dahl-Jensen, an ice expert and professor at the Niels Bohr Institute in Copenhagen, told Reuters. She said ice2sea wrongly assumed a slowdown in the rate of ice discharge from Greenland.
Sea levels rose by 17 cm last century and the rate has accelerated to more than 3 mm a year. A third of the current rise is from Antarctica and Greenland - equivalent to emptying 138 million Olympic-sized pools into the sea every year.
One factor likely to offset sea level rise, ice2sea said, is that warmer temperatures will result in more snow, especially over Antarctica, locking in the moisture on land. It also played down worries of a runaway melt of Greenland, and of the breakup of major Antarctic ice shelves.
Governments want to know future sea levels to plan sea barriers and regulations for everything from vacation homes to nuclear power plants by the coast. And every extra centimetre means big costs.
A Dutch commission planning to bolster sea defences, for instance, has advised spending more than 100 billion euros ($130 billion) by 2100 to strengthen dykes and other barriers for a worst case scenario of a 1.2 metre North Sea rise by 2100.
The ice2sea study also said that a survey of experts' opinions showed there was a less than one-in-20 risk that melting ice sheets would contribute more than 84 cm to sea level rise this century. Taken with thermal expansion, that would mean a sea level gain of just over a metre, Vaughan said.
Almost 200 governments have agreed to work out a U.N. deal, by the end of 2015, to combat global warming that would help limit temperature rises and rising seas.
A leaked report by a U.N. panel of climate scientists, due for release in September and drawing on ice2sea data, estimates sea level rise at between 29 and 82 cm by the late 21st century, above the estimates in its last report in 2007 of between 18 and 59 cm.
Many studies since 2007 have had higher upper numbers, including by the World Bank, the U.S. National Oceanic and Atmospheric Administration (NOAA) and a report for the Arctic Council. NOAA put the upper limit at 2 metres. ($1 = 0.7703 euros) (Editing by Alison Williams)