its mass during 2007 (one km3 of ice weighs about 0.9 Gt). By 2002, the area below the snow line was found to have increased by 16% since the beginning of detailed measurements in 1979. The area of melting in 2002 broke all previous records. The number of glacial earthquakes at the Helheim Glacier and the northwest Greenland glaciers increased substantially between 1993 and 2005. In 2006, estimated monthly changes in the mass of Greenland's ice sheet suggest that it is melting at a rate of about per year. A more recent study, based on reprocessed and improved data between 2003 and 2008, reports an average trend of per year. These measurements came from the US space agency's GRACE (Gravity Recovery and Climate Experiment) satellite, launched in 2002, as reported by BBC. Using data from two ground-observing satellites, ICESAT and ASTER, a study published in Geophysical Research Letters (September 2008) shows that nearly 75 percent of the loss of Greenland's ice can be traced back to small coastal glaciers. Notable calving events had also been recorded in 2000s. For instance, Helheim Glacier in East Greenland had a stable terminus from the 1970s–2000. In 2001–2005 the glacier retreated and accelerated from /day, while thinning up to in the terminus region. Kangerdlugssuaq Glacier, East Greenland had a stable terminus history from 1960 to 2002. The glacier velocity was /day in the 1990s. In 2004–2005 it accelerated to /day and thinned by up to in the lower reach of the glacier. On Sermeq Kujalleq the acceleration began at the calving front and spread up-glacier in 1997 and up to inland by 2003. On Helheim the thinning and velocity propagated up-glacier from the calving front. In each case the major outlet glaciers accelerated by at least 50%, much larger than the impact noted due to summer meltwater increase. On each glacier the acceleration was not restricted to the summer, persisting through the winter when surface meltwater is absent. Between 2000 and 2001, Northern Greenland's Petermann glacier lost of floating ice, and a piece of Petermann suddenly broke away in 2008. Sermeq Kujalleq broke up by 2005, losing in a dramatic event credited by some NASA scientists with raising worldwide awareness of glacial response to global climate change. In 2007, the IPCC Fourth Assessment Report noted that most mass balance estimates indicate accelerating mass loss from Greenland during the 1990s up to 2005. Assessment of