As one might expect, the extent of ice cover on the Arctic Ocean waxes and wanes with the seasons, reaching its annual maximum in March. Of course, as global warming progresses, the ice cover will continue to diminish and, by 2040, the Arctic Ocean is expected to be ice free during the summer months. Indeed, as the Arctic ice gradually disappears, less solar radiation is reflected into the atmosphere, accelerating the rate of Arctic warming.
Following the breakup of Pangea and the opening of our "modern" oceans, the northern Continents had drifted into their current positions by the end of the Cretaceous Period, some 70 million years ago (MYA). Since the global climate remained relatively warm through the early Tertiary Period, Arctic Ocean ice did not begin to form until the late Eocene (about 47 MYA), reaching its maximum extent during the glacial periods of the Pleistocene (2.2 MYA to 10,000 years ago); during warm interglacial periods of the Pleistocene, the Arctic ice may have nearly disappeared, especially through the summer months.
The reduction of Arctic sea ice, in both area and thickness, has accelerated over the past century, as has melting across the Greenland Ice Sheet and the Antarctic ice shelves. Current scientific evidence indicates that human activity (superimposed on the warm interglacial period in which we live) is responsible for this acceleration, which is having a dramatic impact on polar ecosystems. Of course, as the ice melts and sea levels rise, that impact will be transmitted to warmer latitudes as well.
