Antarctic Ice

Many of the world's big cities are built near the ocean. This means that rising sea level caused by climate change threatens the homes and livelihoods of millions of people who live along the coast. According to Professor David Holland, the main sources of water that will lead to elevated sea level are the melting ice sheets of Antarctica and Greenland. Holland and a member of his team from the Center for Global Sea-Level Change (CSLC) at NYU Abu Dhabi have recently published a paper in Nature that found that one of the most sensitive and critical areas of the Earth's ice in West Antarctica is being affected by changes in the north and tropical Atlantic, which has been warming for over 30 years.

Climate change is truly a global phenomenon; changes in one part of the globe can influence climate in another, since ocean currents and winds link distant regions. But the team's conclusion is surprising because initially there is no reason to think that the far-off north and tropical Atlantic would affect Western Antarctica.

But this seems to be the case, and their analysis demonstrates the complexities of global climate, said Holland, who is professor of math and atmospheric ocean science at NYU New York and head of CSLC. The paper's lead author, Xichen Li, is a doctoral student at NYU's Courant Institute of Mathematical Sciences and affiliate of CSLC.

The future of rising sea level will in part be determined by the way the ocean interacts with large ice sheets like the one found in West Antarctica. These massive glaciers flow slowly over land and eventually meet the sea. Where ice sheet meets ocean, warm ocean water speeds up the melting of the ice.

"To date, the focus of our work has been studying the melting of ice sheets on location by carrying out field programs in Antarctica and in Greenland," Holland said. But for the paper published in Nature, the researchers wanted to understand how warm ocean water was being directed to West Antarctic glaciers in the first place.

They started with a problem.

Scientists have long known that the Antarctic Peninsula in West Antarctica is subject to climate change. Indeed, over the past few decades, the Peninsula has warmed more than anywhere on the planet, and this warming has led to the melting of land ice in the area. The sea ice that surrounds the Peninsula, however, has not necessarily declined, but has redistributed itself in odd ways.

Scientists have also known that the climate of this remote region — which lies about 600 miles south of Tierra del Fuego — is affected by changes in the Pacific Ocean, and that changes in the Pacific cause short-term changes to the climate of the Peninsula. But fluctuations in the Pacific couldn't account for the warming of the Peninsula or for the redistribution of sea ice around it. So, for this paper, researchers focused on the Atlantic, which had been overlooked as a force behind Antarctic climate change.

It is remarkable that the recent 30-year trend in North Atlantic Ocean warming is driving climate change in West Antarctica, Holland said. And it's worrying that "West Antarctica is precisely the most sensitive place on Earth for future sea-level change," he added. "This opens the possibility of significant sea-level change of a few meters in the next century, which could have a huge impact on low-lying costal areas."

Holland and his team plan to carry on with the work that was done for the recent paper and to expand on their findings: "We plan to do further climate modeling to help us better understand the connection between the north and tropical Atlantic and the waters off West Antarctica. Moreover, we are trying to develop the capability to project sea-level change for the next century and beyond."

Additional authors of the paper are Edwin Gerber, assistant professor at NYU’s Courant Institute of Mathematical Sciences; and Changhyun Yoo, post-doctoral fellow at the Courant Institute.

In the image above several glaciers in the Antarctic Peninsula pass between sharp mountain peaks and converge in a single calving front, as seen by Operation IceBridge while returning from a survey of the Ronne Ice Shelf on Nov. 1, 2012. NASA's Operation IceBridge is an airborne science mission to study Earth's polar ice. For more information about IceBridge, visit: www.nasa.gov/icebridge. Photograph By: Jefferson Beck/NASA IceBridge, National Science Foundation