'Antarctic sea ice is such a different animal'
For some commentators, the out-of-sync trends in sea ice at the two poles is evidence that warming isn't global and doesn't deserve the international angst it triggers.
Not so fast, many researchers respond. Northern and southern sea ice shouldn't necessarily act in lock-step. "Antarctic sea ice is such a different animal," says Douglas Martinson, another polar-ice specialist at Lamont-Doherty. Geographic and oceanographic differences – a virtually landlocked ocean in the north versus an open ocean in the south – encourage the buildup of thick, long-lasting, multiyear ice in the Arctic Ocean. Antarctica's sea ice, by contrast, is largely thin and seasonal. In winter, Antarctic sea ice covers an area nearly twice the size of Europe. By the end of summer, it shrinks to one-sixth of its winter extent. These wide swings make it difficult to tease out long-term trends in ice cover there.
The first big advance in monitoring Antarctic sea ice came in 1972, when the federal government launched a satellite with a microwave device to monitor ice 24/7, regardless of cloud cover.