evidence: Each year, Arctic sea ice expands as the sea surface freezes during the long, dark winter. At its maximum in March, the ice covers nearly the entire Arctic Ocean, almost 6 million square miles. It melts back during summer, reaching its lowest point in September. In July during the 1980s, the ice covered an average of about 3.8 million square miles, roughly the area of the U.S. or Canada. [...] Arctic sea ice influences climate and weather far beyond the Arctic. Its bright whiteness reflects solar heat back into the atmosphere and insulates the ocean below. The temperature difference between a cold Arctic and the hot tropics drives winds and ocean currents and influences weather globally. [...] The model’s ability to represent the Last Interglacial, in turn, suggests that it can be trusted with the future. When the model was run forward in time, it predicted that Arctic sea ice would all but disappear by 2035.