Shrinkage in key Antarctic Glaciers

Antarctica's ice sheets have been shrinking at a rate of about 1 millimeter per year since 1979, according to data published today in Nature Geoscience. That’s about the same pace of retreat seen over the past 40 years in some mountain ranges around the world, including parts of North America, Europe and Asia.    Researchers say the findings show that the melting of the West Antarctic Ice Sheet (WAIS) is more than just a local phenomenon. WAIS contains enough water to raise global sea levels by 20 feet if it were to melt completely.   Scientists believe that the warming climate may be triggering the collapse of the WAIS. Other researchers have speculated that the WAIS could disappear entirely in the coming decades.  

The new research shows that the WAIS has lost 6 trillion tons of ice since 1978 — almost 2 inches of ice each year. The loss is equivalent to roughly half of all the ice on the entire WAIS at any given point.   Over the past decade, scientists have observed a dramatic increase in the amount of warm air trapped beneath the surface of the WAIS. The influx of warmer air helps explain how the ice sheet melted faster than anticipated during warm summer months. While the study focused on the WAIS, the findings suggest that other major ice sheets in Greenland and East Antarctica could start losing mass soon.  The results add to evidence that the planet is experiencing its warmest temperatures since modern humans evolved, and that changes in the atmosphere are altering the way Earth’s systems work.  

The findings were based on analysis of marine sediment cores taken from the ocean floor off Antarctica’s coast. These cores provide a snapshot of conditions thousands of years ago. In recent years, scientists have estimated that the WAIS loses about 10 billion tons of ice annually. But the new data indicate that the ice sheet is actually losing 12 billion tons of ice each year.  The WAIS covers 11 percent of Antarctica, and holds enough frozen water to raise global sea level by nearly 6 meters. If the entire ice sheet were to melt, it would cause oceans to rise by 23 meters. About two-thirds of coastal cities in the United States lie below sea level, making them vulnerable to rising waters.  Antarctica’s WAIS contains enough ice to cover the state of New Jersey to a depth of 25 meters. However, the region’s ice shelves - floating extensions of land ice that help stabilize the continent - appear stable.