New study finds that atmospheric response to Antarctic ice melt could help mitigate climate change

A new study shows that Antarctic ice melt could significantly affect the atmosphere and weather patterns across the Southern Hemisphere.

In the study, researchers modelled what happens to the atmosphere when large amounts of freshwater from melting Antarctic ice flow into the Southern Ocean. 

The results from nine different climate models show similar patterns: the lower atmosphere cools, while the stratosphere above warms. The first feature strengthens the jet stream, while the second one weakens the stratospheric polar vortex. 

This is important as the jet stream plays a key role in the earth’s climate by keeping cold air separated from warm air. Similarly, a weak polar vortex is weakening the development of the ozone hole.

What the researchers found

When freshwater flows into the seas around Antarctica, the ocean surface cools and sea ice spreads further. This cools the air close to the surface. At the same time, the layer of air just above the troposphere warms. This effect is strongest in winter and spring, when sea ice formation is at its peak.

Study co-author Tore Hattermann from the iC3 Polar Research Hub comments that:

“What gives us confidence in the mechanism is how consistent the signal was across all models. Even though they differ in detail, they all show the same cooling below and warming above once Antarctic meltwater is added.”

“These findings remind us that melting ice in Antarctica will not only raise sea level. It will also change the atmosphere and weather systems far beyond the Southern Ocean.”

The researchers also found that Antarctic freshwater release could have impacts far beyond the Southern Ocean. Their study predicts:

-              A weakening of the stratospheric Polar vortex and thus a decrease in the ozone hole

-              A strengthening of the polar jet stream

-              A cooling of the eastern tropical Pacific Ocean

-              A delay in the potential weakening of the Atlantic Meridonial Overturning Circulation

-              A reduction of the global warming rate

Why the atmosphere responds this way

The cooling near the surface happens because the glacial meltwater input increases the stability of the water column, which reduces the transfer of heat from the deep ocean to the surface. 

This leads to an extension of sea ice cover, which means that more sunlight is reflected back into space, and the ocean releases less heat to the air, making the lower atmosphere contract. 

When that happens, the boundary between the lower (troposphere) and upper (stratosphere) atmosphere shifts downward, compressing the air just above the ocean and thus making it warmer. Drier air there also loses less heat to space, adding to the warming. In winter, winds and atmospheric waves move extra heat into this layer, further strengthening the effect.

Although the researchers added the same amount of freshwater all year round in their models, the changes in the atmosphere varied with the seasons. The size of the sea-ice cover and the behavior of winds and waves shaped how strong the response was.

How the study was done

The team used a set of nine global climate models. Each model ran a long experiment where a steady amount of freshwater was added around Antarctica, and a control run without extra freshwater. Comparing the two made it possible to see how the atmosphere responded. 

The researchers then looked at temperature changes at different heights, water vapour, winds, and circulation patterns to understand what was happening.

Why this matters

These results suggest that Antarctic meltwater can have a significant effect on the atmosphere and the global climate. Cooling in the lower atmosphere and warming higher up could shift winds, storms, and weather patterns across the Southern Hemisphere. Changes in the upper atmosphere may also affect ozone layer recovery.

The study’s finding that Antarctic meltwater is important not only for the ocean, but for the entire Earth system, can help to inform future climate models.

Find out more

The study “Robustness and mechanisms of the atmospheric response over the Southern Ocean to idealized freshwater input around Antarctica” is available open access in Geophysical Research Letters.

The lead author, Xiaoqi Xu, works with the Chinese Academy of Sciences and GEOMAR. iC3 Polar Research Hub’s Tore Hattermann contributed to the study. 

Tore is a researcher at the Norwegian Polar Institute and at the Department of Geosciences at UiT The Arctic University of Norway. His research focuses on ocean-ice interactions in polar regions. He is particularly interested in how physical processes at the ice-ocean boundary affect ice shelf stability and sea-level rise.