What is ‘zombie ice’, how it threatens to raise global sea levels by over 10 inches?

The melting of the Greenland ice sheet will unavoidably raise the global sea levels by at least 10.6 inches or 27 centimetres, no matter what climate action the world decides to take right now. This is because of ‘zombie ice’, which is certain to melt away from the ice cap and blend into the ocean.

The calculation comes from a recent study published in the journal Nature Climate Change (https://www.nature.com/articles/s41558-022-01441-2) where scientists for the first time calculated minimum ice loss in Greenland, and the corresponding rise in global sea level.

What is ‘zombie ice’?

Also referred to as dead or doomed ice, zombie ice is one that is not accumulating fresh snow even while continuing to be part of the parent ice sheet. Such ice is “committed” to melting away and increasing sea levels.

“This ice has been consigned to the ocean, regardless of what climate scenario we take now….more like a foot in the grave,” the lead author of the study, Jason Box, told Associated Press.

What has led to this?

This is on account of warming that has already happened. The research points to an equilibrium state where snowfall from the higher reaches of the Greenland ice cap flows down to recharge edges of the glaciers, and thicken them. It says that over the last several decades there has been more melting and less replenishment.

What happens next, and by when?

By calculating minimum committed ice loss based on the ratio of recharge to loss, the scientists have projected that 3.3% of Greenland’s total ice volume will melt, and this will happen even if the global temperature is stabilized at the current level. But given that global warming is predicted to get worse, the melting and the corresponding rise in sea level could be much worse. The study says it could reach as much as 30 inches (78 centimetres) if Greenland’s record melt year (2012) becomes a routine phenomenon.

However, the research team has not given a timeline. All that it mentions is that this committed melting is likely “within this century”.

But while some have questioned the timeframe being left out as an unknown, others have said the study gives a solid conservative estimate of what is likely to happen.

The approach is “more grounded in what has already happened” than past ice sheet modeling, John Walsh, chief scientist at the University of Alaska Fairbanks, told The New York Times.

What does a 10-inch rise in sea-level mean?

The inevitable sea-level rise that the study predicts is particularly a bad news for millions that live in coastal zones. According to the UN Atlas of the Oceans, 8 of the world’s 10 largest cities are near a coast. Rising sea levels will make flooding, high tides and storms more frequent and worse as their impact will reach more inland. This, in turn, means a threat to local economies and infrastructure. Also, low lying coastal areas will take a harder hit.

The World Economic Forum’s 2019 Global Risks Report noted that “already an estimated 800 million people in more than 570 coastal cities are vulnerable to a sea-level rise of 0.5 metres by 2050”.

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