Washington, Mar 3 (IANS): The sea level may rise twice as high by 2100 as previously estimated as a result of climate change, a new NASA study says.

According to the findings detailed in the journal Proceedings of the National Academy of Sciences, rise in sea level may increase by up to 65 centimeteres in the next 80 years, enough to cause significant problems for coastal cities, Space.com reported on Friday.

"This is almost certainly a conservative estimate," said Steve Nerem, Professor at the University of Colorado-Boulder, who led the NASA Sea Level Change team that conducted the study.

This acceleration has been driven mainly by increased ice melting in Greenland and Antarctica, the study said.

The findings are based on 25 years of NASA and European satellite data.

"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 is not likely," Nerem said in a statement.

Rising concentrations of greenhouse gases in Earth's atmosphere increase the temperature of air and water, which causes sea level to rise in two ways.

First, warmer water expands, and this "thermal expansion" of the ocean has contributed about half of the seven centimetres of global mean sea level rise that has been observed over the past 25 years, Nerem said.

Second, the water from melting land ice flows into the ocean, which also increases sea level around the world.

The rate of sea level rise has risen from about 2.5 millimetres per year in the 1990s to about 3.4 millimetres per year today, the researchers said.

These increases have been measured by satellite altimeters since 1992, including the TOPEX/Poseidon, Jason-1, Jason-2, and Jason-3 missions, which have been jointly managed by NASA, France's Centre national d'etudes spatiales, the European Organisation for the Exploitation of Meteorological Satellites, and the US National Oceanic and Atmospheric Administration.

The researchers said that the speed of the acceleration can be affected by geological events such as volcanic eruptions or by climate patterns such as El Nino and La Nina.

They used climate models and other data sets to account for the volcanic effects and to determine the El Nino /La Nina effects, ultimately uncovering the underlying rate and acceleration of sea level rise.