We should be worried, and it looks increasingly probable that we should be worried – that's what these new studies on the west Antarctic ice sheet tell me.



The interesting thing for me as a glaciologist is that the authors are guys that are normally pretty conservative but – by saying the collapse of the ice sheet has started – have taken it to the next level.

It's long been known there's this potential threat. But until now, it wasn't clear if the ice sheet there was genuinely unstable.

They're talking about a whole extra chunk of sea level rise. It wasn't included in the recent IPCC [UN climate science panel] report, and if you take the higher numbers here it doubles previous sea level rise expectations.

Sea level rise is the single biggest threat to humanity from ice sheets. A collapse of the ice sheets is the largest potential source of sea level rise out there.

Most of the sea level rise we've seen so far is from thermal expansion [ocean warming and therefore expanding] and alpine glaciers melting.

The sea level rise caused by west Antarctica collapsing will change the coastline of the whole world.

The rise won't be even around the world – the coast of north-eastern US and along the south of China will see particularly high increases.

The rise in the sea level itself isn't the most important or damaging aspect – what's important is that it means sea storm surges will have a much greater effect and will be made far more likely. Places that had a one in 100 year risk of a serious storm surge may become a one in 10 years likelihood, meaning people have to abandon that place.

It's not just cities – ecosystems along the coasts will be affected too.



The rise is pretty exceptional in historical terms, at rates that haven't been seen since the end of the last ice age. And this is the first time we are seeing rates like this with a very large human population.

We have to adapt to it. For us as a society, that's a really big deal, it's going to have a destablising effect, it's going to be very expensive, and it's going to be very hard.

There are a couple of caveats in the new papers, around processes that may slow down the collapse. These mean that the authors of both studies cannot be absolutely definitive about the irreversibility of ice loss.

We need to know more about the possible buttressing effect that newly-forming ice shelves will have, which could slow down the ice streams, and we need to have more information on the melting caused by the oceans, which is what’s behind these changes. The authors suggest that these are unlikely to change the big picture of retreat that they describe though.

I'm not very surprised by the new studies. All the signs have pointed towards an ongoing retreat, the forcing is there, and that points towards an increasing loss of ice. Most people thought there was a good chance that instability would kick in. But we didn't know when.

• As told to Adam Vaughan. Hamish Pritchard is a glaciologist for the British Antarctic Survey.

