February 9, 2012
Researchers Taking Stock Of Earth’s Melting Ice
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In a new study led by researchers at the University of Colorado at Boulder, scientists using NASA data have found that Earth´s glaciers and ice caps outside of the regions of Greenland and Antarctica are losing nearly 150 billion tons of ice annually.
Using satellite measurements from the NASA/German Aerospace Center Gravity Recovery and Climate Experiment (GRACE), researchers were able to measure ice loss in all of Earth´s land ice between 2003 and 2010.
What they found is dramatic: the melt-off from the world´s ice sheets, ice caps and glaciers over the past eight years have been enough to cover the entire United States in about 18 inches of water. The data indicates that melting ice has raised sea levels by an average of 0.06 inches per year.
Besides those found in Greenland and Antarctica, glaciers and ice caps around the world are shedding 148 million tons -- or 39 cubic miles -- of ice annually, the researchers said.
Physics professor John Wahr of CU-Boulder, one of the study leaders, said these measurements are important because the melting of the world´s glaciers and ice caps, along with Greenland and Antarctica, pose the greatest threat to sea level increases in the future.
Despite the new evidence, research does show that in some regions, particularly in the snow-capped chain of mountains from Himalayas to Tian Shan on the border of China and Kyrgyzstan, no ice has been lost over the past decade.
The discovery shocked scientists, who believed that nearly 55 tons of melt water were being shed each year and not being replenished with new snowfall.
The Himalayan glacier melt-off caused controversy in 2009 when a report from the United Nation´s Intergovernmental Panel on Climate Change mistakenly stated that they would disappear by 2035, instead of 2350.
However, Wahr said while greater uncertainty has been discovered in Asia´s highest mountains, the melting of ice caps around the world still remains a serious concern.
“Our results and those of everyone else show we are losing a huge amount of water into the oceans every year,” he told Damian Carrington of The Guardian newspaper. “People should be just as worried about the melting of the world´s ice as they were before.”
While the team of scientists did point out that lower altitude glaciers in the Asian mountain ranges were definitely melting, as satellite images and reports confirmed, during the 8-year study, enough ice was added back to the peaks to compensate for the loss.
Wahr warned that eight years of data is a relatively short time period and that variable monsoons mean year-to-year changes in ice mass of hundreds of billions of tons. “It is awfully dangerous to take an eight-year record and predict even the next eight years, let alone the next century,” he told Carrington.
Wahr said the reasoning behind the radical reappraisal of ice melting in Asia comes from different ways in which the current study and previous studies were conducted. Before the new research, estimates of melt water loss for all the world´s 200,000 glaciers were based on analytical data from a few hundred. Lower altitude glaciers were much easier for scientists to study, and so were more frequently included, but were also more prone to melting.
The new study, using GRACE, measured tiny changes in the Earth´s gravitational pull. When ice is lost, the gravitational pull weakens and is detected by the orbiting satellites. “They fly at 500km (310 miles), so they see everything,” Wahr said. “Even though we don´t have the resolution to look at individual glaciers, GRACE has proven to be an exceptional tool.”
“I believe this data is the most reliable estimate of global glacier mass balance that has been produced to date,” said professor Jonathan Bamber of England´s Bristol University. Bamber, who was not involved in the new research, wrote an accompanying commentary, published along with the study, in the journal Nature.
Bamber noted that 1.4 billion people depend on the rivers that flow from the Himalayas and Tibetan plateau. “That is a compelling reason to try to understand what is happening there better.”
“The new data does not mean that concerns about climate change are overblown in any way. It means there is a much larger uncertainty in high mountain Asia than we thought. Taken globally all the observations of the Earth´s ice — permafrost, Arctic sea ice, snow cover and glaciers — are going in the same direction,” he added.
Bamber, in his commentary, noted that the study period was too brief to capture large fluctuations in melting from some areas, such as the Gulf of Alaska and the Himalayas.
“Nonetheless, [the study authors] have dramatically altered our understanding of recent global (glacier and ice cap) volume changes, and their contribution to sea-level rise,” Bamber wrote. “Now we need to work out what this means for estimating their future response.”
The study´s first lead author, Thomas Jacob, completed his research at CU-Boulder and is now at the Bureau de Recherches GÃ©ologiques et MiniÃ¨res, in OrlÃ©ans, France. Other co-authors include Professor Tad Pfeffer of CU-Boulder´s Institute of Arctic and Alpine Research and Sean Swenson, a former CU-Boulder physics doctoral student who is now a researcher at the National Center for Atmospheric Research in Boulder.
The twin satellite system GRACE launched in 2002 and continues to monitor the planet, but has passed its expected mission span and its batteries are beginning to weaken. A replacement program has been approved by US and German space officials and could launch by 2016.
The GRACE satellites were developed by NASA´s Jet Propulsion Laboratory, based in Pasadena, California. The two satellites are in the same orbit, roughly 137 miles apart. The California Institute of Technology manages JPL for NASA.
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