Greenland's ice sheet melted the most it has in over a half century last year, US government scientists said Tuesday in one of a series of "unmistakable" signs of climate change.

"The world continues to warm," the National Oceanic and Atmospheric Administration said in a briefing paper for reporters.

"Multiple indicators, same bottom-line conclusion: consistent and unmistakable signal from the top of the atmosphere to the bottom of the oceans."

An annual climate survey, which includes work by scientists from 45 countries, said that ice sheet in Greenland melted at its highest rate since at least 1958, when similar data first became available.

Arctic sea ice shrank to its third smallest area on record, while the world's alpine glaciers shrank for the 20th straight year, the study said.

In line with previous studies, the survey said that 2010 was also one of the hottest years on record.

Last year was either tied for the hottest or the second hottest on record, depending on methodology. But all methodologies used showed the temperature to be at least 0.9 degrees Fahrenheit (0.5 Celsius) above the average recorded in the three decades through 1990.

The survey noted that 2010 was exceptional for its extreme events, including a deadly heat wave in Russia, floods in Pakistan that displaced more than 20 million people and record snowfall in several US cities.

A series of studies have voiced alarm at the rapid pace of melting in the Arctic Ocean, which could lead to a rise in sea levels that threatens low-lying coastal areas and islands.

The Oslo-based Arctic Monitoring and Assessment Program said in May that warming in the Arctic was on track to lift sea levels by up to 5.3 feet (1.6 meters) by 2100, a far steeper jump than predicted a few years ago.

Many environmentalists have been disappointed at the pace of diplomacy to fight climate change, with few expecting a major agreement at the next major UN-led talks opening in South Africa in late November.

Former US vice president Al Gore recently accused President Barack Obama of failing to show leadership on climate change, saying that poor coverage of the media had given credibility to skeptics of global warming.