According to new research by Colorado State University and National Oceanic and Atmospheric Administration scientists, recent climate changes at the surface of Antarctica are directly tied to changes in wind patterns likely linked to the large ozone hole above the icy continent.
"Recent surface temperature changes over Antarctica can seem confusing," said David Thompson, assistant professor of atmospheric science at Colorado State and lead author of the study. "In some areas temperatures are falling while in other areas temperatures are rising. This research provides a possible explanation for these seemingly inconsistent climate trends."
In the May 3 edition of the journal Science, the researchers report that weather trends in the Southern Hemisphere have been dominated in recent years by the Antarctic Oscillation, a large-scale climate pattern defined by variability in the strength of westerly winds circulating clockwise around the polar cap. The new study shows that this circulation has been changing in systematic ways over the past few decades and that these changes have affected temperatures at the Earth’s surface.
"This research shows that there is a clear trend in the Antarctic Oscillation over the past few decades, and that this trend extends all the way from the Earth’s surface to the stratosphere," said Susan Solomon, co-author of the paper and senior atmospheric scientist at NOAA. "This trend affects surface temperatures, warming some Antarctic areas while cooling others."
Over the past few decades, the Antarctic Peninsula has been warmed by several degrees while the interior of the continent exhibited slight cooling. Ice shelves have retreated over the peninsula and the amount of sea ice has decreased in the Bellingshausen Sea. At the same time, sea ice concentrations have increased over regions of eastern Antarctica and the Ross Sea. Thompson and Solomon show that there are connections between these seemingly disparate events.
The air over Antarctica circulates around a vortex created by the temperature and pressure changes over the cold continent along with the rotation of the Earth. The journal article explains that the vortex has shown a trend toward intensified winds circulating the polar cap. As a result, according to Thompson and Solomon, areas inside the vortex such as the Ross Ice Shelf and eastern Antarctica are cooling. A stronger vortex also implies that more air from the relatively warm ocean is flowing over the Antarctic Peninsula contributing to the warming of that region.
"The trend toward a stronger vortex has contributed substantially to the recent cooling observed over much of Antarctica," said Thompson. "It has also contributed to the warming of the peninsula, but it’s certainly not the whole story in that region."
The westerly circumpolar vortex extends from the surface to the stratosphere and is strongest during midwinter when temperatures are coldest, and weakest during the summer months. The vortex exhibits variability over month-to-month and year-to-year timescales, but has shown a pronounced trend in recent years.
The research goes on to suggest that changes at the Earth’s surface during late spring to early summer may be related to the ozone hole that forms each year over Antarctica. Ozone absorbs incoming radiation and plays a dominant role in heating the stratosphere. However, in the region of the ozone hole, the lack of ozone leads to a far colder stratosphere, strengthening the vortex.
"During late spring, the surface climate trends appear to be related to trends in the stratospheric circulation, which in turn are linked to the ozone hole," said Thompson. "But while ozone appears to be an important player, it is important to note that other climate change mechanisms may also be contributing to the trend in the vortex."