Climate change is causing Greenland ice masses to melt faster, losing four times more ice since 2003, a new study says.

According to research published on Monday in the Proceedings of the National Academy of Sciences, the ice loss in 2012 - more than 400 billion tonnes - reached nearly four times the rate in 2003.

The largest sustained ice loss came from southwest Greenland, a region previously not seen as a crucial actor in rising sea levels as it is mostly devoid of large glaciers.

"We knew we had one big problem with increasing rates of ice discharge by some large outlet glaciers," said Michael Bevis, the study's lead author and a professor of geodynamics at Ohio State University.

"Now we recognise a second serious problem: increasingly large amounts of ice mass are going to leave as meltwater, as rivers that flow into the sea," he said.

The melting of surface mass, which the study's authors said was a consequence of global warming, is set to "become a major future contributor to sea level rise."

"The only thing we can do is adapt and mitigate further global warming - it's too late for there to be no effect," Bevis said, adding "we are watching the ice sheet hit a tipping point".

To analyse changes in ice mass, the study used data from NASA's gravity recovery and climate experiment (known as Grace) and GPS stations scattered across Greenland.

In December 2018, another study published by scientific journal Nature found that runoff from Greenland's ice sheet, which in places is more than 1.6 kilometres thick, now occurs at a volume 33 percent greater than the 20th century alone.

If all of Greenland's vast ice sheet was to melt, global sea levels would rise by seven metres.

Antarctica ice loss

It was the second alarming report on the effect of climate change on sea level rise in a week. On January 15, Eric Rignot, chair of Earth System Science at the University of Irvine, published a study warning that Antarctica is melting about six times more a year now than 40 years ago.

The sea level increased more than 1.4cm between 1979 and 2017.

"As the Antarctic ice sheet continues to melt away, we expect multi-metre sea level rise from Antarctica in the coming centuries," Rignot said.

A rise of 1.8 metres by 2100 - as some scientists forecast in worst-case scenarios - would flood many coastal cities home to millions of people.

The total amount of ice in the Antarctic, if it all melted, would be enough to raise sea levels 57 metres.

Warming ocean water will only speed up ice loss in the future, and analysts say sea levels will continue to mount for centuries, no matter what humans do now to rein in climate change.

Recent research has shown oceans are heating up quicker than previously thought, setting new heat records in the last few years.