The giant ice sheets of Antarctica and Greenland are melting faster than scientists previously estimated, raising the prospect of faster sea level rise placing at risk low-lying areas of Sydney and similar exposed cities around the world.

New research, including from the US National Oceanic and Atmospheric Administration (NOAA), has lifted the "plausible" sea level rise by 2100 to as much as two metres to 2.7 metres.

That has superseded earlier estimates, such as the 2013 Intergovernmental Panel on Climate Change (IPCC), that placed the likely top range of sea level rise at about one metre if greenhouse gas emission rises continued unabated.

Those higher forecasts have now been included in new mapping by Coastal Risk Australia that combines the estimates with national high-tide data and the shape of our coastline.