An international team of researchers has concluded that the Antarctic Ice Sheet actually plays a major role in regional and global climate change — a discovery that may also help explain why sea ice in the Southern Hemisphere has been increasing despite the warming of the rest of the Earth.
The research team’s hypothesis was that climate modelers were overlooking one crucial element in the overall climate system — an aspect of the ocean, atmosphere, biosphere or ice sheets — that might affect all parts of the system or climate change.
The Antarctic Ice Sheet, in fact, has demonstrated dynamic behavior over the past 8,000 years.
There is a natural variability in the deeper part of the ocean adjacent to the Antarctic Ice Sheet — similar to the Pacific Decadal Oscillation, or El Niño/La Niña but on a time scale of centuries — that causes small but significant changes in temperatures.
When the ocean temperatures warm, it causes more direct melting of the ice sheet below the surface, and it increases the number of icebergs that calve off the ice sheet.
Those two factors combine to provide an influx of fresh water into the Southern Ocean during these warm regimes.
The introduction of that cold, fresh water lessens the salinity and cools the surface temperatures, at the same time, stratifying the layers of water.
The cold, fresh water freezes more easily, creating additional sea ice despite warmer temperatures that are down hundreds of meters below the surface.
The discovery may help explain why sea ice has expanded in the Southern Ocean despite global warming.
The same phenomenon doesn’t occur in the Northern Hemisphere with the Greenland Ice Sheet because it is more landlocked and not subject to the same current shifts that affect the Antarctic Ice Sheet.
The Antarctic Ice Sheet covers an area of more than 5 million square miles and is estimated to hold some 60 percent of all the fresh water on Earth. The east part of the ice sheet rests on a major land mass, but in West Antarctica, the ice sheet rests on bedrock that extends into the ocean at depths of more than 2,500 meters, or more than 8,000 feet, making it vulnerable to disintegration.
Scientists estimate that if the entire Antarctic Ice Sheet were to melt, global sea levels would rise some 200 feet.