Polar Ice Melting Much Faster Than Expected
November 30, 2012
Greenland’s ice sheets are melting at a rate five times faster than they were in the 1990’s, according to a new study of polar ice sheets reported in the journal Science. The study, which involved 47 climate scientists from 26 labs around the world, also found that the melting in West Antarctica has accelerated by about 50 percent. The only ice sheet that shows no signs of melting is in East Antarctica, the highest and coldest area on the planet. That ice sheet is actually growing, because rising temperatures have increased snowfall. Warmer air holds more water, so higher temperatures typically increase snowfall in cold areas. However, the small increase in ice there is not enough to offset the loss of ice from West Antarctica. The melting is being caused by global warming—the gradual increase in average temperatures at Earth’s surface. Most climate scientists have concluded that global warming is caused mainly by greenhouse gases released by burning such fossil fuels as coal and oil.
The study found that the melting ice sheets have caused nearly ½ inch (11 millimeters) of the rise in sea level since 1992, or about 20 percent of the overall rise. The scientists cautioned that it is difficult to determine how quickly sea level may rise in the future, largely because of uncertainties about how quickly glaciers will flow into the sea. But there is no question that the rise in sea level has also accelerated. Most climate scientists expect sea level to rise by 3 to 6 feet (1 to 2 meters) by 2100.
The retreat of a mountain glacier can provide visible evidence of global warming. These photographs show two late-summer views of Grinnell Glacier in Glacier National Park, Montana. In the photo taken around 1940, top, Upper Grinnell Lake had only begun to form at the glacier’s end. By 2006, bottom, melting ice had caused the lake to swell in size. Researchers predict that warming will melt all of the park’s glaciers by 2030. (Glacier National Park Archives, top; U.S. Geological Survey, photograph by Karen Holtzer, bottom.)
The new research provides more evidence that the Arctic is warming more quickly than any other area of the planet. In September, scientists at the National Snow and Ice Data Center reported the greatest melt of Arctic sea ice ever recorded. In fact, all six of the record-setting years for melting sea ice have occurred in the last six years. Melting sea ice does not add to rising sea level, because sea ice already floats on ocean water. But warming polar waters eat away at the edges of ice sheets on land, causing glaciers to flow into the ocean more quickly. Ice that melts from land does cause rising sea level.
The research helps to resolve scientific uncertainty about the rate of melting in the polar ice sheets. Different methods of measurement have found somewhat different rates of melting. The new research combined three different sources of data. The first was altimetry, which involves aircraft using lasers to measure the elevation of the ice sheet. Another source was satellites that measure ice using radar. The third source was satellites that measure tiny changes in Earth’s gravitational field. This field varies slightly depending on the mass of ice in a given location. Together, the three methods of measurement show the accelerating loss of polar ice.
Additional World Book articles:
- Kyoto Protocol
- Ice formation
- Intergovernmental Panel on Climate Change
- The Great Meltdown (a Special Report)
- Global warming (2011) (a Back in Time article)
- Global warming (2010) (a Back in Time article)
