Nasa has said that Antarctica's ice sheets are thickening quickly enough to offset the melting caused by global warming. While that's welcome news, it doesn't tell the whole story.

In a study published in the Journal of Glaciology, Nasa scientists used satellite data to find that between 2003 - 2008, there had been a net gain of 82 billion tonnes of sheet ice per year.

The news no doubt thrilled climate change deniers like Republican Senator Jim Inhofe, who once brought a snowball on to the Senate floor to prove climate change is a 'hoax'.

However, the study also shows that between 1992 - 2001, the net gain was 112 billion tonnes of ice, so at the current rate, the gains will only outweigh ice cap loss for a few decades at the most.

On top of that, huge millennia-old ice sheets are still collapsing, and there's evidence that this loss of sea ice could already be having an irreparable effect on Antarctica's interior frozen land ice reservoir.

At the same time the Nasa study was published, computer modelling by the Potsdam Institute for Climate Impact Research found that in western Antarctica, ice sheet collapse may be changing geological stress levels on the continent. That affects how ice moves elsewhere, and could be destabilising the land ice.

And if the land ice melts, the researchers predict massive sea level increases - more than three metres within a few centuries, which would flood vast parts of the Earth.

The new Nasa study that found net ice gains also contradicts a 2013 report by the Intergovernmental Panel on Climate Change (IPCC), which concluded there had been a net loss of 147 billion tonnes of Antarctic ice per year between 2002 - 2011.

Even if Antarctica's melting isn't contributing to sea level rise, the IPCC attributed the 0.27mm sea level rise to ice cap melting last year.

So if the extra water isn't coming from Antarctica, there's something else contributing to sea level rise - and we don't know what it is.

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