January 23, 2014
North Atlantic Warming May Be A Contributor To Antarctic Climate Change
April Flowers for redOrbit.com - Your Universe Online
A team of New York University climatologists has concluded that the gradual warming of the North and Tropical Atlantic Ocean is adding to climate change in Antarctica. The conclusions rely on more than three decades of atmospheric data and reveal new ways in which Antarctic climate change is affected by distant regional conditions.
"Our findings reveal a previously unknown—and surprising—force behind climate change that is occurring deep in our southern hemisphere: the Atlantic Ocean," says Xichen Li, a doctoral student in NYU's Courant Institute of Mathematical Sciences. "Moreover, the study offers further confirmation that warming in one region can have far-reaching effects in another."
The Antarctic region has experienced dramatic climate change over the past few decades, with the peninsula exhibiting the strongest warming of any region on Earth. Greenhouse gas increases and stratospheric ozone loss has been blamed for climate changes during the summer in Antarctica. It is less clear, however, what forces drive the winter climate change. Efforts to uncover the atmospheric culprit are further stifled because the effects of these changes during the cold season are complex.
Scientists have known for a long time that Antarctica's climate is affected, in part, by changes in the distant Pacific Ocean climate. However, the phenomenon created by the Pacific has shorter-term influences, like El Nino. The longer-term forces that have produced warming along the Antarctic Peninsula, or the sea-ice redistribution in the southern hemisphere's winter over the past several decades, are more baffling to scientists.
The NYU team decided to look in a different direction than traditional research: the Atlantic Ocean. So far, the Atlantic had been overlooked as a force behind Antarctic climate change.
The research team looks specifically at the North and Tropical Atlantic's Sea Surface Temperature (SST) variability, which are changes in the ocean's surface temperature. They focused on this metric, the Atlantic Multidecadal Oscillation (AMO), for the last three decades because it had not previously been considered in seeking explanations.
The researchers used a time-series analysis—matching changes in the North and Tropical Atlantic's SST with subsequent changes in the Antarctic climate—finding strong correlations. The team observed changes in sea-level pressure in the Antarctic's Amundsen Sea that followed warming events in the Atlantic waters. They also found that the warming patterns preceded redistribution of sea ice between the Antarctic's Ross and Amundsen-Bellingshausen-Weddell Seas.
According to David Holland, a professor at NYU's Courant Institute and past director of NYU's Center for Atmospheric Ocean Science and past director of NYU's Center for Atmospheric Ocean Science, the study consisted of two parts. These elements incorporated both the use of observational data and computer modeling.
The first portion of the study used observational data to find a correlation between the Atlantic and Antarctic data sets. The researchers caution, however, that a correlation simply means that two things appear to happen in conjunction, but does not explain what may be causing a phenomenon.
A global atmospheric model, which allowed the researchers to create a simulated warming of the North Atlantic, was used in the second part of the study. As the researchers suspected, the model responded by "changing" the climate in Antarctica.
"While our data analysis showed a correlation, it was the use of a state-of-the-art computer model that allowed us to see that North Atlantic warming was causing Antarctic climate change and not vice versa," he said.
The researchers say their findings raise deeper questions. For example, is Antarctic sea-ice change fundamentally different from the well-reported changes in the Arctic? Arctic sea-ice, in contrast to Antarctic sea-ice, had diminished significantly. With declines in some areas and increases in others, the Antarctic ice has redistributed itself in ways that have confused researchers.
"From this study, we are learning just how Antarctic sea-ice redistributes itself, and also finding that the underlying mechanisms controlling Antarctic sea ice are completely distinct from those in the Arctic," Holland concluded.
The study findings were published in a recent issue of Nature.