According to recent research, portions of the Earth’s ice sheets that may raise the world’s oceans by metres are weak in ways that have not before been recognised and will likely collapse with an additional half degree of warming.
The risk, which will manifest across centuries, may also be higher than anticipated for a sizeable section of the world’s population living in coastal regions.
According to recent study, the number of people threatened by sea level rise has likely been overestimated by tens of millions as a result of faulty satellite data interpretation and a lack of scientific resources in poorer nations.
Since 2000, Greenland and Antarctica’s ice sheets have shed more than half a trillion tonnes each year, the equivalent of six glacial Olympic pools every second.
These kilometer-thick ice cubes have surpassed glacier melt as the single most significant driver of sea-level rise, which has increased thrice in recent decades compared to the majority of the twentieth century.
A 20-centimetre rise since 1900 has intensified the devastating wallop of ocean storms, which have become more intense and widespread as a result of global warming, and is pouring saline water into populous, low-lying agricultural deltas across Asia and Africa.
Until far, climate models have underestimated the contribution of ice sheets to future sea level rise because they focused on the one-way influence of rising air temperatures on the ice rather than the complex interplay between atmosphere, seas, ice sheets, and ice shelves.
Using so-called active ice sheet models, scientists from South Korea and the United States predicted how much ice sheets would raise global oceans by 2150 under three emissions scenarios: rapid and deep cuts as advocated by the UN’s IPCC advisory panel, current climate policies, and a sharp increase in carbon pollution.
Looking simply to the year 2100 is deceptive since oceans will continue to rise for hundreds of years regardless of how quickly mankind reduces emissions.
They discovered that if rising temperatures can be limited to 1.5 degrees Celsius over preindustrial levels, the additional impact of ice sheets will be minimal.
Doomsday glacier
However, current policies, including national carbon-cutting pledges under the 2015 Paris Agreement, would add around a half-metre to the global watermark.
Furthermore, if emissions from either human or natural sources grow, enough ice would melt to lift oceans 1.4 metres.
The study’s most notable conclusion, published this week in Nature Communications, was a red line for accelerated ice-sheet breakup.
According to co-author Fabian Schloesser of the University of Hawaii, “our model has a threshold between 1.5C and 2C of warming — with 1.8C as a best estimate — for acceleration of ice loss and sea level rising.”
There are “tipping points” beyond which total collapse is unavoidable, whether in years or millennia, according to scientists who have long studied the West Antarctic and Greenland ice sheets, which together could rise oceans 13 metres. Finding these temperature trip wires, however, has proven difficult.
However, two studies published this week in Nature revealed unexpected fractures in the Thwaites “doomsday glacier” of Antarctica, a slab the size of Britain that is retreating towards the sea.
Thwaites has retreated 14 kilometres since the 1990s and is one of the continent’s fastest moving glaciers. It is prone to irreversible ice loss since a large portion of it is below sea level.
However, due to a lack of information, it is unclear precisely what is causing the march to the sea.
Misinterpretation of data
The vast tongue of ice Thwaites has pushed out over the Amundsen Sea in the Southern Ocean was penetrated by a multinational mission of British and US scientists by a hole 600 metres deep (the height of two Eiffel towers).
They looked at the buried inside of the ice shelf using sensors and an underwater robot named Icefin that was threaded through the breach.
In certain areas, melting was much greater than anticipated, but it was much less in others.
The astounded scientists found long fractures being driven open by the sea water as well as up-side-down staircase structures with accelerating erosion, resembling an underwater Escher drawing.
According to Britney Schmidt, principal author of one of the studies and an associate professor at Cornell University in New York, warm water is seeping into the fissures and causing the glacier to erode at its most vulnerable area.
According to a fourth study, which was just published in the American Geophysical Union journal Earth’s Future, rising ocean levels will dispense with agriculture, contaminate water sources, and relocate millions of people more sooner than previously imagined.
“The time available to prepare for increasing flooding vulnerability may be significantly less than previously believed,” Dutch researchers Ronald Vernimmen and Aljosja Hooijer found.
According to the new analysis, a given amount of sea level rise – whether 30 or 300 centimetres – will damage twice the region predicted by most models to yet.
Surprisingly, data misunderstanding is largely to blame: radar measurements of coastal elevations used until recently frequently misread tree canopy and rooftops for ground level, adding metres of elevation that were not present.
Tens of millions of people in coastal areas of Bangladesh, Pakistan, Egypt, Thailand, Nigeria, and Vietnam will be most susceptible.
Earlier studies using more accurate elevation data discovered that areas currently home to 300 million people will be exposed to flooding exacerbated by climate change by mid-century, regardless of how aggressively emissions are lowered.
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