As scientists watch the world's ice melt away, predict sea level rises, and sound the alarm about climate change, they have been struggled to demonstrate a direct link between that and human activity, at least when it comes to the western Antarctic ice sheets – until now.
Atmospheric warming has been linked by researchers to the loss of ice in the Antarctic Peninsula, the northernmost part of the continent. But air temperatures have remained quite low in the rest of Antarctica, including West Antarctica, causing scientists to look to the ocean as the cause for ice loss there, researchers say.
But authors of a study published Monday in the journal Nature Geoscience have documented changes in the character of the winds that sweep past West Antarctica's most fragile glaciers. They've found that changes in the direction or strength of those winds are altering the ocean water that comes into contact with the ice, causing the glaciers to melt.
Until now, researchers had been stymied by the loss of ice in the western Antarctic because they were studying air temperatures, and those have remained quite low in most of Antarctica, according to a statement from the research team. This time the scientists turned their attention to the ocean that slides by the glaciers, and found some compelling evidence linking human activity to the ice melt.
Natural variations in the winds have a cycle lasting about a decade, but the researchers also documented a "longer-term change in the winds that can be linked with human activities," the researchers said in a statement from the British Antarctic Survey, one of three institutions involved in the study.
They noted that the changes could lead to a significant sea level rise by 2100.
Combining satellite observations with climate model simulations, the research team studied changes in the winds over the ocean near West Antarctica since the 1920s as greenhouse gases have become more concentrated and prevalent.
"Human-induced climate change has caused a long-term change in the winds, and that warm ocean conditions have gradually become more prevalent as a result," the team concluded.
"This is the first evidence for a direct link between human activities and the loss of ice from West Antarctica," said study lead author Professor Paul Holland. "Our results imply that a combination of human activity and natural climate variations have caused ice loss in this region, accounting for around 4.5 cm of sea-level rise per century."
"These results solve a longstanding puzzle," said co-author Eric Steig, a University of Washington professor of Earth and space sciences, in a separate statement. "We have known for some time that varying winds near the West Antarctic Ice Sheet have contributed to the ice loss, but it has not been clear why the ice sheet is changing now."
"We knew this region was affected by natural climate cycles lasting about a decade, but these didn't necessarily explain the ice loss," said study coauthor Pierre Dutrieux of Columbia University's Lamont-Doherty Earth Observatory. "Now we have evidence that a century-long change underlies these cycles, and that it is caused by human activities."
Antarctica has been melting for quite some time, with huge chunks of glacier calving off into the ocean.
The West Antarctic ice sheet contains a good 6% of the world's fresh water, according to National Geographic. Global sea levels would rise by at least 10 feet if it were to melt. While scientists don't expect that to happen soon, Nat Geo said, some parts are more vulnerable than others.
In May, a report showed that nearly a quarter of the western Antarctic ice was unstable.
The latest news wasn't all dire, as long as humans start to listen and change behavior.
"An important finding is that if high greenhouse-gas emissions continue in future, the winds keep changing and there could be a further increase in ice melting," Holland said. "However, if emissions of greenhouse gases are curtailed, there is little change in the winds from present-day conditions. This shows that curbing greenhouse gas emissions now could reduce the future sea-level contribution from this region."