Scientists Find Surprising Reason Sea Ice Melt Could Slow the Pace of Sea Level Rise

While Antarctica has not lost as much sea ice as the Arctic, as global warming progresses, the continent has been losing its ice at a faster rate.

In a surprising new study, scientists from The Pennsylvania State University (Penn State) found that sea ice loss in Antarctica causes an increased amount of snowfall over its ice sheets, which leads to them contributing less to global sea level rise, reported Penn State.

“The Antarctic ice sheet (AIS) is the largest freshwater body on Earth and is a major component of the sea level budget. Since the start of the satellite record in 1980, the AIS has been losing mass at an increasing rate. These losses are attributed to increased flow of ice into the ocean and are partially balanced each year by the accumulation of snow across the ice sheet’s surface. The degree to which it snows across Antarctica therefore controls how much the ice sheet contributes to sea level in any given year,” the authors of the study wrote. “Importantly, our findings show that sea ice declines in this region lead to enhanced moisture in the atmosphere which is then transported over the West Antarctic ice sheet resulting in greater snowfall.”

The study, “Identifying the Impacts of Sea Ice Variability on the Climate and Surface Mass Balance of West Antarctica,” was published in the journal Geophysical Research Letters.

The scientists looked at how decreased sea ice in West Antarctica’s Amundsen Sea affected the surface of the ocean. They found that when it was free of ice, there was more atmospheric moisture, which led to heavier amounts of snow falling on the AIS, Penn State reported.

Luke Trusel, co-author of the study and an assistant professor of geography at Penn State, said there was not enough snowfall to offset the effects of ice melt, but including the additional snowfall in climate models could improve forecasts of sea level rise.

Trusel explained that dramatic processes such as calving — when chunks of ice break free from the ice sheet — often get the most attention, but more discreet events like snowfall can be consequential.

“For a place like Antarctica, which is just massive, the amount of snow falling on top of the ice sheet is as important or even more important than other processes like meltwater or ice breaking off,” Trusel said, as reported by Penn State. “We’re tracking both snowfall and melt to understand both ends of the equation — what takes from sea level and what gets returned to the ocean. We want to know how those factors are impacting the ice sheets.”

Most of the snowfall in Antarctica comes from evaporating ocean moisture, but sea ice plays a crucial role in regulating the process.

“Sea ice is significant,” said Jessica Kromer, lead author of the study and a doctoral candidate at Penn State, as Penn State reported. “It reflects sunlight, aids in cooling the planet and influences interactions between the atmosphere and ocean, including oceanic evaporation. We found that precipitation varies so much year to year. In some years, precipitation can take away from sea level or lessen the impact of the ice discharged from the sheets.”

The researchers used climate data along with satellite observations in their analysis of the relationship between the atmosphere, ocean surface and mass of Antarctica’s ice sheets. They found that during periods when sea ice was reduced, more moisture was retained by the atmosphere. When the moisture reached the colder boundaries of the ice sheet, it condensed, leading to an increase in snowfall.

The researchers said the findings suggest that shrinking levels of sea ice will increase evaporation over the ocean as global temperatures rise, leading to precipitation over the Antarctic continent. Sea levels will still rise, but the increase in snowfall can temporarily mitigate it.

“With global warming, there’s an expectation of reduced sea ice,” Trusel said, according to Penn State. “As sea ice diminishes, there could be increased evaporation from the ocean leading to more precipitation over Antarctica. While this might appear to offset the loss of sea ice, the implications are multifaceted. Increased snowfall in Antarctica might slow the sea level rise, but it’s essential to recognize that the ice sheet will continue to contribute to rising sea levels.”

The researchers pinpointed a feedback loop between water vapor and sea ice. When the ocean surface is free of ice, evaporation is intensified, which contributes to more water vapor. The increase in moisture leads to a local amplification of the greenhouse effect, leading to increased downward longwave radiation, which then reduces sea ice the following month.

Kromer said recent satellite data indicated important changes in sea ice patterns.

“While Arctic sea ice has been rapidly declining over the satellite record, the Antarctic experienced a slight increase until 2015, followed by a sharp decline in 2016,” Kromer said, as reported by Penn State. “In 2022, we witnessed a new record low, and this year’s levels are even lower, significantly below previous observations. These recent rapid changes in Antarctic sea ice highlight the urgency of understanding their causes and their potential impact on the Antarctic ice sheet.”

The researchers said the findings draw attention to the need to refine current climate models in order to improve the accuracy of their predictions.

“If we aim to project future sea level changes with precision, it’s essential to enhance our models, particularly in representing sea ice dynamics,” Trusel said, as Penn State reported.