The National Snow and Ice Data Center, part of a research institute at the University of Colorado Boulder, said satellite records suggest arctic sea ice cover reached its lowest level in recorded history last weekend.
NSIDC researcher Walt Meier said declining seasonal sea ice coverage indicates there are fundamental changes under way in the arctic region.
"The arctic used to be dominated by multiyear ice, or ice that stayed around for several years," he said in a statement. "Now it's becoming more of a seasonal ice cover and large areas are now prone to melting out in summer."
NSIDC said sea ice covered 1.58 million square miles Sunday, 27,000 square miles less than the record set in 2007. While seasonal, researchers said the sea ice decline was a "strong signal of long-term climate warming."
Environmental advocacy group Greenpeace said trends like these can be stopped by investments in renewable energy and energy efficiency.
Global emissions peaked in 2011 to a level 1 gigaton short of a benchmark needed to limit the increase in the average global temperatures to 2 degrees Celsius, the International Energy Agency said.