So if the Antarctic glacier melt is now ‘beyond the point of no return’, why is sea ice at record levels?


rignot-fullIn a previous post, I raised attention to the news that a rise in sea level of more than a metre is now inevitable. But if that’s the case, why is current Antarctic sea ice observations indicating a record amount of sea ice this year? Does this disprove global warming and prove there won’t be a sea level rise?

One way we can have a look at this argument is by comparing sea ice and glacier ice. First of all sea ice forms on the surface of the sea and is floating. It does not contribute to sea level rises as it is already displacing it’s weight in water. As ice it’s only pushing the sea up as much as it would if it was water anyway. On the other hand glaciers are grounded. They are sitting on top of solid rock, rather than floating. See this video of what’s meant by a grounding line. As the ice moves off rock and starts floating on water, it will now begin to displace water. This will push the sea level up by the same amount as if the ice were liquid water added to the sea.

Sea ice is typically 1-2 metres thick in the Antarctic. The glaciers in West Antartica are up 3 kilometres thick. That’s 3000m thick to put it in the same terms. It’s several orders of magnitude bigger.

Sea ice in the Antarctic typically covers between 17-20 million square kilometres in winter, according to the National Snow and Ice Data Centre. So up to 20 million square kilometres of ice that’s around 2 metres thick. A quick calculation puts that at 40 000 cubic kilometres of ice.

The West Antarctic Ice Sheet is estimated to contain 25.4 million cubic kilometres of ice. Why estimated? Because it’s hard to get a precise determination of the land shape under the ice, you can’t get a precise figure. It is the best information we have. The diagram below compares the two.

Comparing Antarctic Sea Ice and West Antarctic Ice Shelf Volume

Comparing Antarctic Sea Ice and West Antarctic Ice Shelf Volume

It gives you a sense of the difference here though. 25 400 000 cubic kilometres of ice is moving faster than ever before and still accelerating towards the sea in just one third of Antarctica.┬áIt’s pretty crazy to suggest that the growth of that ~40 000 cubic kilometres around the whole continent is evidence against Antarctic melting.