the data and techniques suggests a mass balance for the Greenland Ice Sheet ranging between growth of 25 Gt/yr and loss of 60 Gt/yr for 1961 to 2003, loss of 50 to 100 Gt/yr for 1993 to 2003 and loss at even higher rates between 2003 and 2005. Since 2010 A sheet of ice measuring broke off from the Petermann Glacier in northern Greenland in August 2010. Researchers from the Canadian Ice Service located the calving from NASA satellite images taken on August 5. The images showed that Petermann lost about one-quarter of its 70 km-long (43 mile) floating ice shelf. Another large ice sheet twice the area of Manhattan, about , broke away from that glacier in July 2012. In July 2012, melt zone extended to 97 percent of the ice sheet's cover. Ice cores show that events such as this occur approximately every 150 years on average. The last time a melt this large happened was in 1889. This particular melt may be part of cyclical behavior; however, Lora Koenig, a Goddard glaciologist suggested that "...if we continue to observe melting events like this in upcoming years, it will be worrisome." This was the first directly observed example of what came to be known as a "massive melting event": the ice core research most melting events before the 21st century were localized rather than widespread across the bulk of the Greenland ice sheet. At the end of 2012, the analysis of gravity data from GRACE satellites indicated that the Greenland ice sheet lost approximately 2900 Gt (0.1% of its total mass) between March 2002 and September 2012. The mean mass loss rate for 2008–2012 was 367 Gt/year.In 2015, Jakobshavn Glacier calved an iceberg about thick with an area of about . A 2013 Nature study identified a contribution from the optically thin liquid-bearing clouds to the extent of ice melt during July 2012. In 2016, another paper suggested that clouds in general enhance Greenland ice sheet's meltwater runoff by more than 30% due to decreased meltwater refreezing in the firn layer at night. In 2018, it was also found that the observed Greenland surface melt was affected by a darkening albedo (and thus increased absorption of thermal radiation), as the regions covered in dust, soot, and living microbes and algae grew by 12% between 2000 and 2012. In 2019, another mass melting event (covering more than 300,000 square