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Aerial view of the Totten Ice Shelf during the 61st Japanese Antarctic Research Expedition in late 2019. Totten contributes to ice loss in East Antarctica, but this was offset by the increased snowfall from 2021 to 2023.
Photo Credit: Yoshihiro Nakayama
Scientific Frontline: Extended "At a Glance" Summary: Antarctic Ice Mass and Climate Variability
The Core Concept: A recent brief period of net ice mass gain in Antarctica was driven by a temporary anomaly in tropical ocean temperatures rather than a long-term reversal of climate-driven ice loss.
Key Distinction/Mechanism: While global warming is expected to eventually increase atmospheric moisture and snowfall at the poles, researchers determined that the excess snowfall between 2021 and 2023 was caused by natural, cyclical warming in the tropical warm pool, which altered atmospheric circulation patterns, directing more moisture to East Antarctica.
Major Frameworks/Components:
- Ice Mass Balance: The net change in an ice sheet's mass, determined by the difference between accumulation (snowfall) and ablation (melting and calving).
- Tropical Warm Pool: A large area of warm ocean water in the western Pacific and eastern Indian Oceans that significantly influences global weather patterns.
- Isotope Tagging: A computational method used by researchers to trace the origins of atmospheric moisture (water molecules) falling as precipitation.
- Natural Climate Variability: Cyclical fluctuations in the climate system, distinct from long-term anthropogenic climate change.
Branch of Science: Earth Sciences, Atmospheric Science, Climatology, and Glaciology.
Future Application: Improving the accuracy of global climate models and long-term sea-level rise projections by correctly differentiating short-term natural climate variability from long-term anthropogenic trends.
Why It Matters: The Antarctic Ice Sheet stores the majority of Earth's freshwater and represents the greatest source of uncertainty in projecting future sea-level rise; correctly interpreting changes in its mass is crucial for global climate predictions.
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| Excess snowfall accumulated over East Antarctica between July 2021 and April 2023. Green indicates above-average precipitation, while brown shows below-average precipitation. Image Credit: Yunhe Wang |
Between 2021 and 2023, Antarctica appeared to be growing. Heavy snowfall fueled by wetter weather caused parts of the continent to gain mass, leading some to question whether climate change is really causing the ice to melt. However, a new study shows that the precipitation increase was an anomaly related to unusually warm tropical ocean temperatures, not part of a long-term trend.
Antarctica has been “shrinking” for decades as warm water melts ice from below and sends large chunks crashing into the ocean. Annual precipitation cannot keep up with the rate of melt, causing a net mass loss. However, the snow that fell on East Antarctica, a vast area that contains nearly 80% of Earth’s land-bound ice, added mass faster than the ice was melting. Although mass loss continued in West Antarctica, the general trend seemed encouraging.
“In the early 2020s, there was an exceptional amount of snowfall over parts of Antarctica. Because Antarctica is so big, it doesn’t take that much extra snow thickness to counter the loss of ice from the edges of the ice sheet, which led to the perception that the loss of ice is slowing down,” said coauthor Eric Steig, a University of Washington professor of Earth and space sciences.
The question nagging researchers was whether this would continue into the future. To answer it, they needed to trace the origins of the precipitation.
Because warm air can hold more moisture than colder air, higher latitudes could eventually see wetter conditions due to global warming. Scientists recognize that the average amount of moisture in the air will increase as global temperatures rise. Some saw the heavier snowfall as evidence that this expected trend was materializing in Antarctica.
“Warmer conditions favor storms shifting toward the poles, which could offset ice loss through snowfall,” said coauthor Qinghua Ding, a professor of atmospheric and climate science at the University of California, Santa Barbara.
But the data told a different story. Using a computational method that involves “tagging” water molecules, the researchers linked the extra precipitation in Antarctica to the tropical warm pool, a warm patch of ocean in the western Pacific and eastern Indian oceans that makes an outsized contribution to extreme weather.
Water temperature in the warm pool was notably higher than average between 2021 and 2023, triggering changes in atmospheric circulation that directed more moisture toward East Antarctica.
Historical evidence shows that multiyear warming of the warm pool is normal. Every few decades or so, it heats up for several years before reverting to its average temperature.
“When something changes, it is very tempting, even to scientists, to think, ‘Oh, there’s a new normal happening,’ but this analysis shows that’s not the case. This is most likely a short-lived phenomenon,” Steig said.
The connection to global warming from human activity is tenuous, he added. It is difficult to tease apart human impact from natural variability in the tropics, but because we see this pattern repeated in history, it is most likely just part of the natural background variability of the tropical climate system.
However, researchers have connected increased carbon dioxide emissions to the climatic conditions accelerating ice loss in West Antarctica.
As a whole, the Antarctic Ice Sheet covers an area larger than the United States and Mexico combined and stores most of Earth’s freshwater. It is also the greatest source of uncertainty in long-term sea-level rise projections. Understanding the balance between ice gain and loss in Antarctica helps researchers make predictions with global implications. Knowing the underlying dynamics provides important guidance for how to interpret new observations.
“There hasn’t been much attention paid to the particular mechanism we identify; this is a reminder to not interpret short-term change as a long-term trend,” Steig said.
“The climate system is complex,” Ding said. “Every year brings new surprises, and we have to stay curious, humble, and open-minded to improve our theories.”
Funding: This study was funded by the National Natural Science Foundation of China, the US National Science Foundation, the US National Oceanic and Atmospheric Administration, the US National Aeronautics and Space Administration, JST PRESTO, Japan, the Japanese Ministry of Education, Culture, Sports, Science and Technology, and the Hungarian Academy of Sciences.
Published in journal: Nature
Title: Multiyear tropical warm pool warming drives slowdown in Antarctic mass loss
Authors: Yunhe Wang, Qinghua Ding, Xiaofeng Li, Thomas J. Ballinger, Yoshihiro Nakayama, Dániel Topál, and Eric J. Steig
Source/Credit: University of Washington | Gillian Dohrn
Edited by: Scientific Frontline
Reference Number: es081926_01
