A 345-square-mile iceberg — 10 times larger than Manhattan — has broken off from Antarctica’s Ross Ice Shelf, the National Ice Center reported Friday. The Ross Ice Shelf is one of two large ice fields on the continent that have seen increased calving of massive icebergs in recent years, which some scientists suggest could be linked to human-caused global warming. As Ross Gelbspan writes in Grist, the melting and calving of ice fields at both poles and other signs of climate change are finally getting through to a number of corporate executives and the general public. But why aren’t the two major party candidates for president drawing attention to the issue?