Nature World: With winter at its end, it appears that the extent of Arctic sea ice has reached its limit. Worryingly, it's the lowest extent ever seen, reaching only about 5.61 million square miles. What's more, this is also one of the earliest maximum extents ever reached, with most seen much further into the end of the season.
Arctic sea ice is pretty self explanatory: it's frozen seawater that grows on the surface of the Arctic Ocean between fall and winter, and gradually recedes at the end of this period....