Scientists say that in the 25 years from 1997 to 2021, 71 of the 162 ice shelves surrounding Antarctica shrank in size, releasing a net of 7.5 trillion tons of meltwater into the ocean. They found that nearly all ice shelves on the west side of Antarctica were losing ice. In contrast, the amount of ice on most of the ice shelves on the east side remained the same or increased.
This graph shows water temperatures around Antarctica. On the west side of Antarctica, the water temperature on the seafloor is close to 2 degrees Celsius, which is hot enough to melt the ice flowing above. The water temperature on the east side is cooler. Source: Dr Benjamin Davison/University of Leeds.
Over those 25 years, scientists calculated that nearly 67 trillion tons of ice was exported to the ocean, offset by an additional 59 trillion tons of ice on ice shelves, resulting in a net loss of 7.5 trillion tons.
An animated video shows how the ice around Antarctica has changed over the past 25 years and summarizes the research project's findings. Image credit: PlanetaryVisions/European Space Agency
Dr Benjamin Davison, a researcher at the University of Leeds who led the study, said: "The picture of ice shelf degradation is mixed and has to do with ocean temperatures and currents around Antarctica. The western half of Antarctica is exposed to warm water, which can quickly erode the ice shelf from below, while much of East Antarctica is currently protected by the cold water belt on the coast from the erosion of nearby warm water."
Geographic and climatic differences
Antarctica is a vast continent, with an area 50 times the size of the United Kingdom. The ocean currents and wind directions in the west side of the sea are different from those on the east side, which causes the seawater temperature under the ice shelf on the west side to rise.
Dr Davidson, a polar Earth observation expert at the School of Earth and Environment, said: "We expected that most ice shelves would undergo a rapid but brief cycle of contraction and then slowly re-grow. Instead, we saw that almost half of the ice shelves were shrinking with no signs of recovery."
Antarctica's total summer surface area is about 14.2 million square kilometers (about 5.5 million square miles), which is much larger than the continental United States, about twice that of Australia, and 50 times that of the United Kingdom. Antarctica is the highest, driest, coldest, windiest and brightest place among the seven continents. It was completely covered by a layer of ice that averaged over a mile thick, and was nearly three miles thick in places. This layer of ice has accumulated over millions of years of snowfall. The Antarctic ice sheet currently contains 90% of the Earth's ice, and if it melted, global sea levels would rise by more than 200 feet. Source: NASA/Goddard Space Flight Center Scientific Visualization Studio LIMA data provided by: Patricia Vornberger (National Center for Scientific Research): Patricia Vornberger (SAIC) LIMA data are produced by the United States Geological Survey (USGS), the British Antarctic Survey (BAS), and the National Aeronautics and Space Administration (NASA).
He believes that human-induced global warming is likely to be a key factor in the disappearance of ice. If it's due to natural changes in climate patterns, there should be some signs of ice regrowth on the western ice shelf. Ice shelves float in the sea around Antarctica and are extensions of the ice sheet that covers much of the continent. Ice shelves act like giant "plugs" at the ends of glaciers, slowing their flow into the ocean. When ice shelves thin or shrink in size, these "plugs" weaken, causing glaciers to lose ice faster.
Researchers observed some of the largest ice losses on the Getz Ice Shelf, which lost 1.9 trillion tons of ice during the 25-year study period. Only 5% of this is due to calving, when large chunks of ice break off ice shelves and enter the ocean. The rest is caused by melting at the base of the ice shelf.
Satellite image showing the Getz Ice Shelf. During the 25-year study period, the Goetz Ice Shelf lost 1.9 trillion tons of ice. This image is a composite of satellite data recorded between January and September 2023. Image source: European Space Agency
Similarly, the Pine Island Ice Shelf also lost 1.3 trillion tons of ice. About a third of that - 450 billion tons - is due to ice sheet breakup. The rest is caused by melting at the base of the ice shelf.
By comparison, the Amélie Ice Shelf on the other side of Antarctica gained 1.2 trillion tons of ice. The waters around it are much colder.
Major assessment of Antarctica
Researchers analyzed more than 100,000 satellite radar images to conduct a major assessment of the ice shelf's "health." If the ice shelves disappear or even shrink, it will have major knock-on effects on Antarctica's ice systems and global ocean circulation, a giant "conveyor belt" that carries nutrients, heat and carbon away from this sensitive polar ecosystem.
Water released into the ocean from ice shelves and glaciers is freshwater. During the 25-year study period, the researchers estimated that 66.9 trillion tons of fresh water flowed into the Southern Ocean around Antarctica from the ice shelves alone.
In the Southern Ocean, dense saltwater sinks to the bottom of the ocean as part of the global ocean conveyor belt. The sinking of seawater is one of the engines driving the ocean's conveyor belt.
Freshwater from Antarctica dilutes the salt in the ocean water, making it fresher and lighter, which takes longer to sink, weakening ocean circulation systems.
Another study published in the journal Nature Climate Change suggests this process may have already begun.
Professor Anna Hogg from the University of Leeds is also one of the authors of the study: "This study makes important findings. We usually think of ice shelves advancing and retreating periodically. Instead, what we see is continuous loss due to melting and breakup. Many ice shelves have already Severe degradation: 48 ice shelves have lost more than 30% of their initial mass in just 25 years This study provides a baseline measurement from which we can see further changes that may occur as the climate warms."
Information about the changes that have occurred in Antarctica in recent years comes mainly from the CryoSat-2 and Sentinel-1 satellites, which monitor Antarctica even on cloudy days and long polar nights.
CryoSat-2, launched in 2010, was the European Space Agency's first exploration mission and the first dedicated to monitoring Earth's polar ice sheets and glaciers.
Professor Noel Gummeren from the University of Edinburgh and Earthwave, one of the study's co-authors: "CryoSat-2 is an excellent tool for monitoring polar environments. Its ability to precisely map the erosion of ice shelves by the ocean below enables precise quantification and zoning of ice shelf losses, while also revealing fascinating details about how this erosion occurs."
The detail captured by these satellite sensors is so rich that scientists are able to track changes in Antarctica from year to year.
Dr. Mark Drinkwater, Head of Earth and Mission Science at the European Space Agency (ESA), said: "Monitoring and tracking climate change over the vast Antarctic continent requires a satellite system that captures data regularly throughout the year. Europe's Copernicus programme's Sentinel-1 satellite mission meets this need. Together with ESA's predecessors ERS-1, -2 and Together with the historical data acquired by environmental satellites, Sentinel-1 has revolutionized our ability to assess the floating ice shelf as a bellwether for the mass balance and health of the Antarctic ice sheet. In the near future, we will further enhance monitoring of the Antarctic through three new polar missions, CRISTAL, CIMR and ROSE-L."