Previously Unknown Loss of Antarctic Ice Discovered by NASA – “Antarctica Is Crumbling at Its Edges”

The biggest unknown in global sea level rise predictions is how quickly Antarctica's ice sheet will melt as the planet warms. The results of two analyses conducted by scientists at NASA's Jet Propulsion Laboratory (JPL) in Southern California provide unexpectedly fresh information regarding the Antarctic Ice Sheet's recent mass loss.

A recent study in the journal Nature illustrates how the Antarctic shoreline has evolved over the past 25 years as a result of iceberg calving, or the breaking off of ice from a glacier front. The ice sheet's edge has been losing icebergs more quickly than it can be replaced, the scientists discovered. With this unexpected discovery, the amount of ice that has been lost from the Antarctic's floating ice shelf since 1997 has increased from 6 trillion to 12 trillion metric tons. The ice shelves have become weaker due to ice loss through calving, allowing Antarctic glaciers to flow more quickly into the ocean and hastening the rate of sea level rise worldwide.

The other study, which was just published in the journal Earth System Science Data, demonstrates in unprecedented detail how the Antarctic ice sheet has almost doubled in size in the western portions over the past ten years as ocean water melting has spread from the continent's outer edges into its interior. The complementing reports work together to give the most comprehensive picture yet of how the frozen continent is evolving.

According to JPL researcher Chad Greene, primary author of the calving study, "Antarctica is collapsing at its edges." And the continent's enormous glaciers tend to accelerate and enhance the rate of the rise in the ocean's surface when ice shelves weaken and shrink.

The majority of Antarctic glaciers flow into the ocean, where they freeze into shelves of ice that can be up to 2 miles (3 km) thick and 500 miles (800 km) across. Glaciers are supported by ice shelves, which prevent the ice from slipping into the ocean. When an ice shelf is stable, it goes through a natural cycle of calving and restocking that keeps its size largely constant over time.

The Antarctic ice sheet's elevation changes between 1985 and 2021 are displayed. Ice height increases (blue) where accumulation outweighs melting, but it decreases (red) as the ice sheet melts when in touch with ocean water. The ice shelves are displayed in gray. The missions that provided the data are mentioned below. NASA/JPL-Caltech credit

The ice shelves of Antarctica have been weakened and made thinner by melting from below in recent decades as a result of the warmer ocean. There hasn't been a thorough analysis of how climate change might be affecting calving across the continent, even though satellite altimeters track the thinning process by monitoring the changing height of the ice.

The difficulty in interpreting satellite imagery is one of the causes. For instance, Greene said, "imagine trying to distinguish between a white iceberg, white ice shelf, white sea ice, and even a white cloud in a satellite image. That's always been a challenging job. However, we now have enough information from several satellite sensors to draw a precise image of how the shoreline of Antarctica has changed recently.

Greene and his coworkers used satellite images of the continent from 1997 in the visible, thermal infrared (heat), and radar wavelengths for the current study. They documented the boundaries of ice shelves along 30,000 linear miles (50,000 kilometers) of the Antarctic coastline by fusing these observations with knowledge of ice flow obtained from an ongoing NASA glacier mapping effort.

The researchers believe it is improbable that Antarctica will grow back to its pre-2000 extent by the end of this century since losses from calving have substantially exceeded natural ice-shelf expansion. All of Antarctica's greatest ice shelves look to be destined for significant calving events in the next 10 to 20 years, according to the findings, which also imply that much bigger losses might be anticipated.

Almost 3 billion data points from seven spaceborne altimetry instruments were integrated in the companion study by JPL researchers to create the longest continuous data collection on the changing height of the ice sheet, a sign of ice loss, going back to 1985. The highest-resolution monthly maps of ice loss change ever made were created using centimeter-accurate radar and laser readings of ice elevation.

Under the massive ice sheet covering Antarctica, hundreds of meltwater lakes can be found. NASA's Ice Cloud and Land Elevation Satellite-2 (ICESat-2) is assisting researchers in "seeing" beneath the ice by using a potent laser altimeter instrument in space.

The new record's unmatched level of detail shows how long-term trends and yearly weather patterns affect the ice. Even the rise and fall of the ice sheet is depicted in the animation above, which shows how subglacial lakes kilometres below the surface frequently fill and empty. As the study's principal author, Johan Nilsson of JPL remarked, "Small changes like this, along with a better knowledge of long-term patterns from this data set, will help researchers understand the processes that impact ice loss, leading to improved future projections of sea level rise."

Years of work and countless processing hours on NASA's servers were required to synthesize and analyze the enormous measurement archives into a single, high-resolution data set. All of the effort was worthwhile, in Nilsson's opinion: "Condensing the data into something more broadly useful may bring us closer to the huge discoveries we need to better understand our planet and to help prepare us for the future implications of climate change."

By JET PROPULSION LABORATORY