格陵蘭冰蓋 幾乎全部出現融化◎聯合（2012.07.25）

格陵蘭冰蓋 幾乎全部出現融化◎聯合（2012.07.25）
http://udn.com/NEWS/WORLD/WOR4/7247958.shtml

科學家表示，格陵蘭島（Greenland）本月發生一起反常事件，覆蓋這座島嶼表面的浩大冰蓋，幾乎每個部分都突然開始融化。

即使格陵蘭島最寒冷的地方也有融化跡象。紀錄顯示，上次出現這種現象是在1889年，這種現象約每150年出現一次。

美國國家航空暨太空總署（NASA）表示，3枚衛星看到7月8日起4天中的「空前」融化景觀。厚冰部分大多維持原樣，但是不尋常的是，廣泛地區出現融化。

航太總署說，融化地區從7月8日的約40%，劇增至4天後的97%。截至目前，衛星過去30年來所看到的最廣泛融化比例，約是55%。

科學家仍無法確定，此一反常融化是由全球暖化引起，還是自然現象。

航太總署與大學科學家分析3枚衛星的測量數據。

航太總署的嚴山（Son Nghiem，譯音）表示，在分析印度太空研究組織（Indian Space Research Organisation）Oceansat-2衛星的數據時，他注意到7月12日格陵蘭島表面大部分地區似乎都在融化。

冰川學家凱尼格（Lora Koenig）：「上次出現這種現象是在1889，這次來的正是時候。但是如果未來幾年仍觀察到這樣的融化現象，那就可憂了。」

全文網址: 格陵蘭冰蓋 幾乎全部出現融化 | 國際萬象 | 全球觀察 | 聯合新聞網 http://udn.com/NEWS/WORLD/WOR4/7247958.shtml#ixzz21cbBHyCe

Satellites See Unprecedented Greenland Ice Sheet Surface Melt◎NASA（2012.07.24）
http://science.nasa.gov/science-news/science-at-nasa/2012/24jul_greenland/

July 24, 2012: For several days this month, Greenland's surface ice cover melted over a larger area than at any time in more than 30 years of satellite observations.  Nearly the entire ice cover of Greenland, from its thin, low-lying coastal edges to its two-mile-thick center, experienced some degree of melting at its surface, according to measurements from three independent satellites analyzed by NASA and university scientists.

On average in the summer, about half of the surface of Greenland's ice sheet naturally melts.  At high elevations, most of that melt water quickly refreezes in place.  Near the coast, some of the melt water is retained by the ice sheet and the rest is lost to the ocean.  But this year the extent of ice melting at or near the surface jumped dramatically.  According to satellite data, an estimated 97 percent of the ice sheet surface thawed at some point in mid-July.

Researchers have not yet determined whether this extensive melt event will affect the overall volume of ice loss this summer and contribute to sea level rise.

"The Greenland ice sheet is a vast area with a varied history of change.  This event, combined with other natural but uncommon phenomena, such as the large calving event last week on Petermann Glacier, are part of a complex story," said Tom Wagner, NASA's cryosphere program manager in Washington.  "Satellite observations are helping us understand how events like these may relate to one another as well as to the broader climate system."

Son Nghiem of NASA's Jet Propulsion Laboratory in Pasadena, Calif., was analyzing radar data from the Indian Space Research Organisation's (ISRO) Oceansat-2 satellite last week when he noticed that most of Greenland appeared to have undergone surface melting on July 12.  Nghiem said, "This was so extraordinary that at first I questioned the result: was this real or was it due to a data error?"

Nghiem consulted with Dorothy Hall at NASA's Goddard Space Flight Center in Greenbelt, Md. Hall studies the surface temperature of Greenland using the Moderate-resolution Imaging Spectroradiometer (MODIS) on NASA's Terra and Aqua satellites. She confirmed that MODIS showed unusually high temperatures and that melt was extensive over the ice sheet surface.

Thomas Mote, a climatologist at the University of Georgia, Athens, Ga; and Marco Tedesco of City University of New York also confirmed the melt seen by Oceansat-2 and MODIS with passive-microwave satellite data from the Special Sensor Microwave Imager/Sounder on a U.S. Air Force meteorological satellite.

The melting spread quickly.  Melt maps derived from the three satellites showed that on July 8, about 40 percent of the ice sheet's surface had melted.  By July 12, 97 percent had melted.

This extreme melt event coincided with an unusually strong ridge of warm air, or a heat dome, over Greenland.  The ridge was one of a series that has dominated Greenland's weather since the end of May.  "Each successive ridge has been stronger than the previous one," said Mote.  This latest heat dome started to move over Greenland on July 8, and then parked itself over the ice sheet about three days later.  By July 16, it had begun to dissipate.

Even the area around Summit Station in central Greenland, which at 2 miles above sea level is near the highest point of the ice sheet, showed signs of melting.  Such pronounced melting at Summit and across the ice sheet has not occurred since 1889, according to ice cores analyzed by Kaitlin Keegan at Dartmouth College in Hanover, N.H. A National Oceanic and Atmospheric Administration weather station at Summit confirmed air temperatures hovered above or within a degree of freezing for several hours July 11-12.

"Ice cores from Summit show that melting events of this type occur about once every 150 years on average.  With the last one happening in 1889, this event is right on time," says Lora Koenig, a Goddard glaciologist and a member of the research team analyzing the satellite data.  "But if we continue to observe melting events like this in upcoming years, it will be worrisome."