Pasadena, California – The greatest uncertainty in global sea level rise predictions is how ice loss from Antarctica will accelerate as the climate warms.
Two studies published on August 10 and led by researchers at the National Aeronautics and Space Administration’s (NASA) Jet Propulsion Laboratory in Southern California reveal unexpected new data on how the Antarctic ice sheet lost mass. over the past decades.
A study, published in the journal Nature, maps how iceberg calving – the breaking up of ice from a glacial front – has altered the Antarctic coastline over the past 25 years. The researchers found that the edge of the ice cap was losing icebergs faster than the ice could be replaced.
The startling discovery doubles previous estimates of ice loss from Antarctica’s floating ice shelves since 1997, from 6 trillion to 12 trillion metric tons. Ice loss from calving has weakened ice shelves and allowed Antarctic glaciers to flow faster into the ocean, accelerating the rate of global sea level rise.
The other study, published in Earth System Science Data, shows in unprecedented detail how thinning Antarctic ice as ocean water melted spread from the outer edges of the continent to its interior, nearly doubling in western portions of the ice sheet over the past. decade. Combined, the complementary reports provide the most comprehensive view yet of how the frozen continent is changing.
“Antarctica is collapsing at its edges,” says JPL scientist Chad Greene, lead author of the calving study. “And when the ice shelves shrink and weaken, the continent’s massive glaciers tend to accelerate and increase the rate of global sea level rise.”
Most of Antarctica’s glaciers flow into the ocean, where they end in floating ice shelves up to 3 kilometers thick and 800 kilometers in diameter. Ice shelves act as buttresses to glaciers, preventing ice from simply sliding into the ocean. When ice shelves are stable, they have a natural cycle of calving and replenishment that keeps their size fairly constant over the long term.
But in recent decades, ocean warming has destabilized Antarctica’s ice shelves by melting them from below, making them thinner and weaker. Satellite altimeters measure the thinning process by recording the changing height of the ice, but until this study there has been no full assessment of how climate change might affect calving on the continent. .
This is partly because satellite imagery has been difficult to interpret. “For example,” Greene said, “you can imagine looking at a satellite image and trying to figure out the difference between a white iceberg, a white ice shelf, a white pack ice, and even a white cloud. It’s always been a difficult task, but we now have enough data from several satellite sensors to get a clear picture of how the Antarctic coastline has changed in recent years.
For the new study, Greene and his co-authors synthesized satellite imagery of the continent in the visible, thermal infrared (heat) and radar wavelengths since 1997. Combining these measurements with an understanding of the flow ice acquired through an ongoing NASA glacier mapping project, they mapped the edges of ice shelves for about 30,000 linear miles (50,000 kilometers) of the Antarctic coast.
Losses from calving have so outstripped natural sea ice growth that researchers believe Antarctica is unlikely to return to its pre-2000 extent by the end of this century. In fact, the results suggest that greater losses can be expected: Antarctica’s largest ice shelves all appear to be heading for major calvings within the next 10 to 20 years.
Mapping 36 years of ice loss
In the companion study, JPL scientists combined nearly 3 billion data points from seven space-based altimetry instruments to produce the longest continuous dataset of ice sheet height change – an indicator of ice loss – as early as 1985. They used radar and laser measurements of ice elevation, accurate to centimeters, to produce the highest resolution monthly change maps of ice loss ever.
The unparalleled detail of the new record reveals how long-term trends and annual weather conditions affect the ice. It even shows the rise and fall of the ice sheet as subglacial lakes regularly fill and empty miles below the surface. “Subtle changes like these, combined with a better understanding of long-term trends in this data set, will help researchers understand the processes that influence ice loss, leading to better future estimates of sea level rise. sea level,” said lead author Johan Nilsson of JPL. of the study.
Synthesizing and analyzing the massive archive of measurements into a single, high-resolution dataset took years of work and thousands of hours of computation on NASA servers. Nilsson says it was worth it: “Condensing the data into something more broadly useful can bring us closer to the big breakthroughs we need to better understand our planet and help us prepare for the future impacts of climate change. »