A new study of Antarctica, including the first map of iceberg calving, doubles previous estimates of weathering of ice shelves and details the change of the continent.
The greatest uncertainty in forecasting global sea level rise is how ice loss from Antarctica will accelerate as the climate warms.
Two studies published on August 10 and led by researchers at NASA’s Jet Propulsion Laboratory in Southern California reveal unexpected new data about how the Antarctic ice sheet has been losing mass in recent decades.
A study, published in the journal Nature, maps how iceberg calving (the calving of ice from the front of a glacier) has changed the Antarctic coastline over the past 25 years. The researchers found that the edge of the ice sheet has been shedding icebergs faster than the ice can be replaced.
This amazing find doubles previous estimates of ice loss from Antarctica’s floating ice shelves since 1997, from 6 billion to 12 billion metric tons. Ice loss from calving has weakened ice shelves and allowed Antarctic glaciers to flow more rapidly into the ocean, accelerating the global rate of sea level rise.
The other study, published in Earth System Science Data, shows in unprecedented detail how the thinning of Antarctic ice as ocean water melts has spread from the continent’s outer edges into its interior, nearly doubling in western parts. of the ice sheet in the past decade. Combined, the supplemental reports offer the most comprehensive view yet of how the frozen continent is changing.
"Antarctica is falling apart"JPL scientist Chad Greene, lead author of the iceberg calving study, says in a statement. "And when ice shelves shrink and weaken, the continent’s massive glaciers tend to accelerate and increase the rate of global sea level rise.".
Most Antarctic glaciers empty into the ocean, where they end in floating ice shelves up to 3 kilometers thick and 800 kilometers wide. Ice shelves act as buttresses for glaciers, preventing the ice from simply sliding into the ocean. When ice shelves are stable, they have a natural cycle of shedding and replenishment that keeps their size fairly constant over the long term.
But in recent decades, ocean warming has been destabilizing 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 comprehensive assessment of how climate change might be affecting iceberg calving across the continent.
That’s partly because satellite images have 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, white sea ice, and even a white cloud. That has always been a difficult task. But now we have enough data from multiple satellite sensors to see a clear picture of how Antarctica’s coastline has evolved in recent years.".
For the new study, Greene and his co-authors synthesized satellite images of the continent in visible, infrared thermal (heat), and radar wavelengths from 1997. Combining these measurements with an understanding of ice flow gained from an ongoing project mapping NASA Glaciers mapped the edges of ice shelves around 50,000 linear kilometers of the Antarctic coastline.
Losses from calving have so far outpaced the natural growth of the ice shelf that researchers they believe it is unlikely that Antarctica will be able to grow back to its pre-2000 extent by the end of this century. In fact, the findings suggest that further losses can be expected: Antarctica’s largest ice shelves appear to be on track for major calving events in the next 10 to 20 years.
In the companion study, JPL scientists combined nearly 3 billion data points from seven space-borne altimetry instruments to produce the longest continuous data set on the changing height of the ice sheet, an indicator of the ice loss, since 1985. They used radar and laser measurements of ice elevation, accurate to centimeters, to produce the highest resolution monthly ice loss change maps ever made.
The unparalleled detail in the new record reveals how long-term trends and annual weather patterns 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 ice level rise. from sea"said Johan Nilsson, lead author of the study at JPL.
