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 say. 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 released on Monday by the National Snow and Ice Data Centre and Nasa. The government-backed ice centre, based at the University of Colorado at Boulder, says 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 kilometres, some 70,000 square kilometres less than the earlier record charted on September 18, 2007. Scientists say the record is all the more striking as 2007 had near perfect climate patterns for melting ice, but the weather this year has been unremarkable other than a storm in early August. Michael Mann, a climate change scientist, says the latest data shows that "alarmist" scientists may have shown "perhaps too great a degree of reticence".