The great defrost: Mridula Ramesh, on the perils of a melting Antarctica - Hindustan Times
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The great defrost: Mridula Ramesh, on the perils of a melting Antarctica

Mar 02, 2024 12:34 PM IST

It's been a rapid slide for the continent of ice, which was expanding until 2014. Mridula Ramesh on an ancient past, near future,and trade-offs to be made today

Antarctica — the continent of extremes and contradictions — tells the story of how climate affects life on Earth. It is the world’s coldest and driest continent. Yet, it holds most of the planet’s fresh water, frozen in the giant, kilometres-thick ice sheet that covers its land. This water is, and should remain, largely frozen, because from our perspective, the problem starts when it begins to melt.

Sea ice reached a new low last year – the fourth new low here in seven years. The continent of ice is crumbling at its edges. One of these chunks is A23a (see aerial view above). The world’s largest iceberg – about four times the size of Delhi – is currently drifting and melting into the Southern Ocean. (Courtesy Ian Strachan / Eyos Expedition)
Sea ice reached a new low last year – the fourth new low here in seven years. The continent of ice is crumbling at its edges. One of these chunks is A23a (see aerial view above). The world’s largest iceberg – about four times the size of Delhi – is currently drifting and melting into the Southern Ocean. (Courtesy Ian Strachan / Eyos Expedition)

To understand why, let’s go back in time. For much of the time between 270 million years ago (mya) and today, forests grew in Antarctica. A 2016 United States Geological Survey report describes coal deposits in East Antarctica, which are essentially the fossilised remains of ancient forests. Seed fossils of the genus Glossopteris, an extinct plant that grew between 290 and 250 mya, have been discovered there. Fossil remains of the Lystrosaurus, a hardy herbivore that resembled a cross between a Komodo dragon, a turtle and a pig, have also been found.

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Then, in a real back-to-the-future scenario, a massive eruption occurred about 250 mya in the Siberian Traps, causing a huge spike in atmospheric carbon worldwide, which led to lethal greenhouse-gas heating.

In the millennia that followed, most life on Earth perished, in what is now called the Great Dying. Cool Antarctica may have served as a refuge. Fossils recovered here from this period include the Kombuisia antarctica, a small egg-laying herbivore with a beak. Earth turned into a hothouse without polar ice caps. The ice held in those sheets melted, causing sea levels to rise tens of metres higher than their levels today.

Life flourished in Hothouse Earth, but it was a different kind of life: colossal cold-blooded reptiles ruled while mammals cowered in fear. Hothouse Earth indicates what might happen if we don’t act on climate. Antarctica shows what might happen next.

***

In March 2022, a demonic heatwave ravaged Antarctica, causing temperatures to rise to as much as 40 degrees Celsius above normal. Fortunately, the heatwave struck in winter, and temperatures remained too low to cause widespread melting. But scientists think it caused the Conger Ice Shelf to collapse.

Ice shelves are formed when a glacier or an ice sheet pours into the ocean. They fringe the Antarctic coastline, acting as mini dams, holding back and delaying the melting of glaciers and ice sheets themselves.

From time to time, calving occurs, when parts of an ice shelf break away to form icebergs. But collapses, like the one from last March, are rarer and troubling. Especially since this is happening in East Antarctica, the more stable side.

Meanwhile, on the unstable side of the continent, a study by the British Antarctic Survey (BAS) found that deep warm ocean water was destabilising the West Antarctic Ice Sheet (WAIS), so much so that even stringent greenhouse-gas emission cuts may not be enough to save it.

Antarctica in winter; September 2023. (NASA / Scientific Visualization Studio)
Antarctica in winter; September 2023. (NASA / Scientific Visualization Studio)

When WAIS melts, sea levels could rise by about 5 metres, submerging parts of the world, including Shanghai, Kolkata, large parts of Florida and about half of Bangladesh. This collapse could become one of Earth’s tipping points, a development that indicates that the planet has reached a new equilibrium, akin to whether or not one is diabetic. With similar ramifications for our planet’s health.

Other scientists still think parts of WAIS may not collapse, and any collapse would take centuries to occur… too long for our short attention spans to care about.

***

But another shift is already underway. Take a look at the image above, of Antarctica as seen in a satellite view. The white gleams in contrast with the dark seawater, because snow and ice reflect sunlight, while water absorbs it. This reflectivity of ice, known as albedo (from the Latin “albus”, meaning “white”), plays a crucial role in keeping Earth cool.

As glaciers grow, the albedo effect cools their surrounds, helping them expand. Indeed, some 650 mya, a runaway albedo effect caused glaciers to cover practically the whole planet, turning Earth into something resembling the planet Hoth in the Star Wars universe.

The inverse can also occur easily. When ice sheets melt, white turns black, warming the waters, causing more melting, and so on, until the ice sheets disappear. This is what likely contributed to Hothouse Earth.

A 2021 paper published in Nature Geoscience shows that we may be in the early phases of such a cycle. Recent developments in satellite remote sensing have enabled scientists to reliably assess changes in Earth’s energy balance. This technology has been used to gain a better understanding of how changes in the reflectivity of polar regions affect this energy balance.

Researchers confirmed that at the North Pole, as a result of melting ice, a darker Arctic Ocean was absorbing more heat. They also found that this heating was offset by the cooling caused by the still expanding Antarctic sea ice pack. Until 2014. Then things changed.

In 2016, the annualised average extent of the Antarctic sea ice pack hit a record low. It hit another in 2017. Another in 2022 and yet another in 2023.

Antarctic cooling was no longer counteracting Arctic warming. Aku Riihelä of the Finnish Meteorological Institute, who led this study, tells me that, while the data analysis is not final, it would be safe to say that the change in reflectivity of the polar regions in recent years was adding as much heating as 20% of the present carbon-dioxide-caused heating, up from about 10% in prior decades.

Sriharikota, we have a problem.

***

Bryant Coast in November and December. The sea ice broke up in December, over a month early, leading to the death of about 9,000 emperor penguin chicks in a record-setting die-off. (Sentinel-2 L2A; NSIDC; Richard Sidey / Eyos; Falklands Maritime Heritage Trust / National Geographic)
Bryant Coast in November and December. The sea ice broke up in December, over a month early, leading to the death of about 9,000 emperor penguin chicks in a record-setting die-off. (Sentinel-2 L2A; NSIDC; Richard Sidey / Eyos; Falklands Maritime Heritage Trust / National Geographic)

There are already tragic victims of this change. Antarctica’s sea-ice cycle has been dubbed the “beating heart” of the planet, as it swells in the austral winter (peaking in mid-September) and then melts, reaching a low in February. Between September and February, about 15 million sq km of sea ice melt. (That’s more than four times the size of India.)

Sea ice melting does not cause sea levels to rise, but the dynamics affect the nutrient cycle, both in the Antarctic and globally, thanks to the giant ocean currents. Poignantly, sea-ice melting affects emperor penguins, who rely on this ice to breed.

There are few places on Earth as hostile as Antarctica’s sea ice in the dead of winter, which is when and where these penguins breed and lay their eggs. The chicks are born as winter warms to spring, in about July-August, but a chick’s coat becomes waterproof only by December-January. Which leaves them vulnerable to hypothermia and drowning when sea ice melts early, as is happening more often.

In 2022, a study used satellite remote sensing to track five penguin-chick colonies in the Bellingshausen Sea and found them thriving in early November. But by early December, four colonies appeared to have been abandoned. In three of these sites, sea ice had disappeared. Indeed, sea ice in the Bellingshausen Sea at this time was at its lowest since records began.

In any given year, most penguin chicks die. That’s the lot of an emperor penguin. But here, entire colonies perished; about 9,000 chicks were lost. With only about 200,000 breeding pairs left, that is substantial.

The emperor penguin is a great example of life clinging on despite the odds. And now it appears to be losing its grip. That’s as disheartening a message as one can get.

***

So much of our understanding of our climate comes from studying Antarctica. Let me end with two key elements of such study: ozone levels and ice cores.

Our discovery of the ozone hole came from BAS observations that showed a dramatic thinning of the ozone layer over Antarctica in the late 1970s. We know that stratospheric ozone shields life from ultraviolet radiation, so this was a problem. BAS meteorologist Jonathan Shanklin and colleagues wrote a report in the mid-1980s linking chlorofluorocarbons to Antarctica’s ozone hole. Within two years, world leaders ratified the 1987 Montreal Protocol, for the phasing out of ozone-depleting compounds.

Now here’s the twist. Given the severity of the changed climate and the fact that emissions are not falling fast enough, some are proposing what was considered a fringe theory, of cooling the climate by injecting dust into the stratosphere to block out some incoming sunlight (a technique called stratospheric aerosol injection or SAI).

There are any number of dangers to this approach, including the possible weakening of the Indian monsoon, and a widening of the Antarctic ozone hole. Indeed, a 2022 report published by a group including the World Meteorological Organisation, the United Nations Environment Programme and others suggested that such an injection of dust could take the ozone hole right back to its largest extent. Talk about unhelpful action.

On to ice cores: Scientists have drilled down into Antarctic ice and retrieved air pockets, to study climate and greenhouse-gas concentrations over 800,000 years. They have dug into sea beds around Antarctica (and elsewhere) to extract fossils of tiny molluscs called foraminifera, to study prehistoric climate over half a billion years.

About 56 mya, they found, global temperatures were about 8 degrees Celsius higher than today. Atmospheric carbon-dioxide levels were at roughly 560 ppm. We are currently at 422 ppm. Without drastic emissions cuts, we could hit 560 ppm this century.

Now the tale gets darker. Scientists have found that warming was somewhat milder in the tropics and much higher at the poles. They further found that most of our current climate models were missing this polar amplification. This means that the bleak future that models project are, if anything, too optimistic. All of which tells us that we should cut emissions unless we want to get to Hothouse Earth again. And yet, there is talk of how all the melting will make it easier to mine for minerals in Antarctica. Well, hell may have oodles of gold — but you’d still have to go there to get it. Makes this trade-off pretty straightforward, doesn’t it?

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