In the remote, alien area of the world where the Amundsen Sea meets the coast of West Antarctica, tall, frozen cliffs loom over the water. They are the edges of massive glaciers—rivers of ice that spill into the ocean. In recent years, these icy rivers have been flowing and melting at an alarming rate, threatening to add a substantial amount of water to the sea that would eat away at global coastlines.
For a long time, scientists had suspected that man-made climate change was likely causing this area of West Antarctica’s ice to thin, but they had not established a direct connection or mechanism. The issue is critical because this is where the majority of the continent’s ice loss is occurring. Now a new study published this week in Nature Geoscience appears to have solved the puzzle. A team of researchers in the U.S. and the U.K. found that global warming has caused a shift in wind patterns that are ultimately bringing more warm ocean water into contact with the region’s ice.
Climate scientists first began to notice that all was not right with West Antarctica’s ice a couple of decades ago, but its melt proved a bit enigmatic. For the most part, air temperatures are still too cold for surface melting to explain why the ice is thinning. That fact suggested the ocean was likely the culprit—yet the top layer of seawater is also too cold to thaw the ice. And while there is a deeper layer of warm ocean water that sometimes reaches the Amundsen Sea and laps away at the undersides of two giant glaciers in the region—called Pine Island and Thwaites—rising global temperatures were not directly warming that water.
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“This is an area where the [warm] ocean waters that melt the ice have been out of contact with the atmosphere for thousands of years,” explains Paul Holland, an ice-ocean scientist at the British Antarctic Survey and one of the authors of the new study. “They're very old waters, so they wouldn’t have been [heated] by global warming.” Thus, the question for Holland and his team was if—and how—climate change had affected these deep-ocean waters. They suspected that wind might be the missing connection.
Holland and his colleagues combined wind data, satellite observations of sea-ice drift and climate-model simulations to understand how wind patterns near Antarctica have evolved since the 1920s (which is how far back the simulations extend) and how any changes may have affected glaciers that flow into the Amundsen Sea. They compared different simulations to parse which effects came from natural fluctuations in the climate versus anthropogenic climate change.
They found that wind patterns indeed appear to have changed over the past century—and in a way that can explain the increased melting of the West Antarctic ice sheet. In the 1920s, the team reports, the winds over the Amundsen Sea would have predominantlyblown toward the west, mostly keeping the warm ocean water at bay. But today the wind patterns flip-flop between blowing eastward and westward. When the waters blow toward the east, the deep layer of warm ocean water can creep in. “When the wind blows east, you get these rivers of warm water coming into the [Amundsen Sea] and melting the ice,” Holland explains. “It’s basically like turning on a hot tap when the wind blows toward the east and turning off the tap when the wind blows toward the west.”
The reason climate change is causing this shift is because of the fundamental way wind works on the earth and responds to warming, Holland says. The earth’s surface is warming unevenly, which influences where areas of high and low pressure are situated in the atmosphere overhead. Because winds flow between those highs and lows, warming affects the broad patterns of winds across the globe. In West Antarctica, warming is shifting a key band of winds southward and making it stronger, which ultimately causes the winds over the Amundsen Sea to blow east.
Other scientists say that this study provides critical insights into what is going on in Antarctica and what could continue tohappen as the planet warms. While many questions remain, “this study increases our scientific confidence that the retreat of West Antarctic ice contributing to sea-level rise was triggered by human-caused global warming,” says Richard Alley, ageoscientist at Pennsylvania State University,who also studies Antarctica but was not involved in this work.
Ted Scambos, a senior research scientist at the University of Colorado Boulder,who was also not involved with the new study, agrees. “We had been able to detect that Pine Island and Thwaites [glaciers] were thinning rapidly and flowing faster,” he says. “Something had changed, and they’re maybe starting down the road of taking all the ice off West Antarctica. How did that happen?” The study’s findings are “a good framework for the climate events that lead to ice loss from this area of West Antarctica,” he adds.
The region’s future is, to some degree, in our hands. The study authors also looked at how Antarctica’s wind patterns would respond if humans are able to reduce the production of greenhouse gases—or if they do not do so. “If we carry on emitting greenhouse gases at an uncontrolled rate, then by 2100, we’ll have winds that reliably blow toward the east”—meaning the winds that bring in the layer of deep warm water, Holland explains. But if humans rein in their emissions so that they start falling by 2050 and ultimately stabilize at half of the current rate, wind patterns could be kept in their current state. “It will require some serious and urgent effort on the part of humankind,” Holland says, “but is less ambitious than the target of the Paris climate agreement.”
That stabilized point may still not be an ideal situation, because West Antarctic ice is already melting at a faster rate than it would have without a human-altered climate—yet it is better than nothing. “If we are able to restrict the amount of further warming, then the effects of this change in the future will be less extreme,” says Scambos, who is co-leading a major study of Thwaites Glacier. “We probably can’t stop everything, but we can put the brakes on if we begin to act.”