A world-leading glaciologist visiting New Zealand says scientists are fast running out of time to fully understand dramatic changes under way in climate change's sleeping giant: Antarctica.

Professor Eric Rignot, based at the University of California, Irvine and NASA's Jet Propulsion Laboratory, will this week give a free talk in Wellington, outlining growing concerns scientists have about the frozen continent and pressing the urgent case for action on climate change today.

Rignot has studied the world's largest glaciers in Greenland and Antarctica since the early 1990s, when NASA and other international space agencies first started collecting satellite data on them.

He is best known for ground-breaking research in 2014 which revealed the rapidly melting section of the West Antarctic Ice Sheet appeared to be in an irreversible state of decline, with nothing to stop the glaciers in this area from melting into the sea.

In an interview with the Herald, Rignot said while historical measurements stretched back a century, some of the most worrying discoveries in Antarctica had come only in recent decades.

The first evidence of warmer water causing melting at Pine Island Glacier, now known to be responsible for a quarter of Antarctica's ice loss, was made in 1996.

The glacier is part of the 25 million square kilometre West Antarctic Ice Sheet, which satellite measurements estimate is losing more than 150 cubic km of ice each year.

Rignot further noted the first physical measurements of warmer water affecting the much larger East Antarctic Ice Sheet, at Totten Glacier, were recorded only in 2015.