Nasa has published satellite images showing unprecedented thawing of the Greenland ice sheet during July. Over a period of four days, between 8 and 12 July, the extent of the thawing changed from about 40% of the ice sheet surface to 97%

The satellite pictures revealed that almost the entire ice cover of Greenland, from its thin, low-lying coastal edges to its two-mile-thick centre, experienced some degree of melting at its surface. The change was so dramatic the scientists at first believed the images were wrong.

“This was so extraordinary that at first I questioned the result: was this real or was it due to a data error?” commented Son Nghiem at Nasa’s jet propulsion laboratory in Pasadena, California.

Usually about half of Greenland’s ice sheet melts naturally during the summer months, but the melting in July was so extensive that the area around the summit station in the centre of the country, which is two miles above sea level and near the highest point of the ice sheet, also showed signs of thawing.

Such pronounced melting at the summit and across the ice sheet has not occurred since 1889, says Nasa.

“Ice cores from the summit show that melting events of this type occur about once every 150 years on average,” commented Lora Koenig, a Goddard glaciologist and a member of the research team analysing the satellite data. “But if we continue to observe events like this in upcoming years, it will be worrisome.”

Scientists believe the rapidly melting ice was due to a heat dome, which produced unusually warm air and hovered over Greenland from 8 July until 16 July, and could be a further indication of a warming climate.

Separate research by the Netherlands Environmental Assessment Agency reveals that global emissions of carbon dioxide increased by 3% in 2011, reaching an all-time high of 34 billion tonnes. The top five emitters are China (29%), the US (16%), the European Union (11%), India (6%) and the Russian Federation (5%).

New data from the Scottish government, meanwhile, show that in 2010 Scotland’s emissions of the six Kyoto greenhouse gases – CO2, methane, nitrous oxide, hydrofluorocarbons, perfluorocarbons and sulphur hexafluoride – were 55.7 million tonnes of CO2 equivalent, a 5.8% increase on the 2009 figure.

Between 1990 and 2010, however, there was a 22.8% reduction in emissions.