Polar ice melt offers unexpected solution to a global climate disaster

The Atlantic Meridional Overturning Circulation (AMOC), a system of Atlantic Ocean currents that redistributes heat and nutrients between the tropics and the North Atlantic, is one of the planet’s tipping points. That means there is a critical threshold that, once crossed, could trigger abrupt, irreversible climate shifts.

According to predictions, melting of the Greenland Ice Sheet (GIS) could destabilize the AMOC. However, new research published in the journal Science Advances suggests that meltwater from the West Antarctic Ice Sheet could prevent it from collapsing altogether.

Meltwater threat

Scientists have known for some time that the GIS poses a significant threat to AMOC. When its meltwater pours into the North Atlantic, it can slow down or stop the sinking of dense water that helps drive this ocean current system. But less well known was whether the West Antarctic Ice Sheet (WAIS), located far away in the Southern Ocean, could also influence AMOC. So scientists from Utrecht University in the Netherlands decided to model what would happen if both Greenland and Antarctica started melting rapidly.

The researchers used a complex computer model, CLIMBER-X (an Earth system model of intermediate complexity, or EMIC), to examine how the AMOC would respond to different speeds and timing of ice sheet collapse.

Stabilizing effect

The most significant finding was that the West Antarctic Ice Sheet’s meltwater didn’t always increase the risk of an AMOC collapse. Under some conditions, such as when its melting was rapid and began to slow down as Greenland’s melt peaked, it could prevent a total collapse.

This happens because Antarctic meltwater changes how layers of water behave in the Southern Ocean, which eventually sends slightly saltier water toward the North Atlantic. Over time, this helps the water stay dense enough to keep the AMOC moving, at least in the model. However, even with this stabilizing effect, the AMOC weakens by about 60% and would take about 3,000 years to recover.

The finding confirmed similar results from previous, simpler conceptual models. “Our results clearly demonstrate that the AMOC stabilization driven by WAIS meltwater fluxes is not only present in conceptual models, but can also be found in EMICs,” wrote the researchers.

Timing is key

However, if the timing is wrong, such as if the WAIS melt peaks too late or is too slow, this stabilizing effect vanishes. In fact, WAIS meltwater could even accelerate the AMOC’s tipping point.

Even though this would be catastrophic, the study’s authors emphasize that WAIS melt itself is far worse. “Such a marked event is far too dangerous to bet on given its many severe consequences including, for example, a total contribution to global sea level rise of up to 4.3 m.”

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