Tuesday, June 11, 2024
Year : 2, Issue: 24
by Quamrul Haider
Punishing heatwaves is not the only measure of global climate change that is undergoing an abnormally rapid change. Numerous other indicators, such as violent storms, long-lasting droughts, devastating floods, raging wildfires, and permafrost thawing, among others, suggest a more general global warming trend. An indicator that does not get much attention but will nevertheless have reverberating effects across the globe is the melting of glaciers and ice sheets, particularly in Antarctica.
As climate change drives global temperatures ever higher, glaciers and ice sheets in the polar and mountainous regions will inevitably melt. According to a paper published in Nature Climate Change (June 2020), Antarctica has warmed at over three times the global rate since 1989. As a result, glaciers in Antarctica, which contain about 90 percent of all the ice on Earth, are flowing into the oceans where they melt and raise the sea level. From 1979 to 1989, some 40 billion tonnes of glacial ice in Antarctica melted each year. A study published in 2019 in the Proceedings of the National Academy of Sciences reported that the amount jumped to 252 billion tonnes each year starting in 2009.
Since 1880, global sea levels have risen roughly 23 centimetres. Over the past decade, the sea level is rising at a much faster rate of 3.9 millimetres per year, as measured by NASA’s satellite-based radar altimeters. The rise is mostly due to a combination of water melting from glaciers and ice sheets, as well as thermal expansion of seawater as it warms.
Scientists are particularly concerned about Thwaites Glacier, a massive block of ice in West Antarctica, approximately the size of Florida. It is nicknamed the “Doomsday Glacier” because if it were to collapse and melt, it could single-handedly cause global sea levels to rise by as much as 65 centimetres. As one of the fastest melting glaciers currently losing 50 billion tonnes of ice annually, Thwaites already accounts for four percent (0.15 millimetre) of the planet’s sea level rise. In the 1990s, it was losing just over 10 billion tonnes of ice a year.
When all the glaciers in Antarctica will melt, sea level will rise some 70 metres, according to the US Geological Survey. Moreover, if the rest of the glaciers on Earth melts too, 7.6 metres will be added on top of Antarctica’s drastic total, wiping out most of the low-lying countries in the world, while in urban settings along coastlines, it will threaten infrastructure vital for local jobs and regional industries.
The coastal edge of Thwaites that interacts with the ocean stretches 120 kilometres, while its thickness from bedrock to surface measures between 800 metres and 1,200 metres. A platform of ice called an ice shelf that floats above the Pine Island Bay acts as a brace, holding this frosty goliath back on the land, thereby slowing its journey to the sea. Thwaites also acts as a natural dam to the surrounding ice in West Antarctica and hence provides an important defence against the sea-level rise.
Ice shelves are highly vulnerable to a warming ocean. Accordingly, scientists believe that a complete collapse of Thwaites’ ice shelf will spell the beginning of the end for the glacier. Without its ice shelf, the glacier will discharge all of its ice into the Amundsen Sea, which, after melting, will be devastating for coastal communities around the world. That is why scientists are interested in studying the interaction between ice shelves and oceans in an increasingly hotter world, in part because they are concerned about the stability of the ice shelves of Antarctica’s other glaciers.
In a study published in May 2024 in the journal Proceedings of the National Academy of Sciences, researchers at the University of California, Irvine, using high-resolution images from satellites and hydrological data, found evidence of the intrusion of warm, high-pressure seawater at depths many kilometres beneath the grounded ice of Thwaites, causing “vigorous melting.”
The widespread contact between the warm seawater and the glacier is rapidly melting the submerged ice at the underbelly and detaching it from the bedrock. In other words, seepage of warm water under Thwaites’ base is “eating away at the ice shelf,” which, in turn, is slackening its grip on the underwater seamount that keeps the glacier stable. Consequently, it is highly probable that Thwaites could disintegrate much faster than previously thought, six times faster than in the 1980s.
The researchers also noted the development of cracks and crevasses on the ice shelf of Thwaites, indicating that it is being structurally weakened. Because cracking and fracturing can have reinforcing feedback effect, the ice shelf will be further weakened, thus hastening its disintegration. Indeed, all evidences suggest that the ice shelf’s “final collapse” could occur sooner rather than later, probably in less than a decade.
The findings by the researchers are alarming because the disintegration of Thwaites due to the deadly punch-jab-uppercut combination of melting from below, ice-shattering and eroding ice shelf could trigger the collapse of other glaciers held in check by Thwaites, potentially raising the global sea level by more than three metres in the coming decades. This is surely an ominous sign of the impending effects of climate change from the world’s largest glacier.
Previous computer models that forecast Thwaites’ future did not account for seawater intrusions past the grounding line, which is the boundary between grounded and floating ice, although a study a decade ago concluded that such intrusions could double the speed of the glacier’s melting. It is therefore expected that findings from all the studies will be used to fine-tune models to predict the Doomsday Glacier’s future and make projections about sea-level rise more accurate.
Finally, there may be uncertainties about exactly what will happen in West Antarctica because predicting the speed of ice loss of glaciers and sea-level rise is not an easy task. And modelling glaciers, which are hydrologically dynamic, remote, and difficult to study, is a technological challenge. Yet, one thing is for sure. Glaciers will accumulate snow in winter and lose ice to melting in summer. But in a warming climate, melting will outstrip accumulation, resulting in a net loss of ice, thereupon adding to the already rising global sea levels.
Author is professor emeritus at Fordham University in New York, US.
