The sea ice in the Arctic Ocean has melted to its smallest point ever in a milestone that may show that worst-case forecasts on climate change are coming true, US scientists said Monday.

The extent of ice observed on Sunday broke a record set in 2007 and will likely melt further with several weeks of summer still to come, according to data from the National Snow and Ice Data Center and the NASA space agency.

The government-backed ice center, based at the University of Colorado at Boulder, said in a statement that the decline in summer Arctic sea ice “is considered a strong signal of long-term climate warming.”

The sea ice fell to 4.10 million square kilometers (1.58 million square miles), some 70,000 square kilometers (27,000 square miles) less than the earlier record charted on September 18, 2007, the center said.