NASA recently announced that 97 percent of Greenland’s vast ice
sheet had undergone at least some surface melting this summer,
compared with a normal melt area of about 50 percent. The 2012
figure, said the headline on the space agency’s press release,
was “unprecedented.” That’s a powerful word in any context, but
it’s especially so when you’re talking about the politically
charged topic of climate change. If the melting was
unprecedented, it would reinforce the idea that scientists are
right about the dangers of human-generated greenhouse gases, and
at the same time make it harder for skeptics to take potshots at
the science. The skeptics were naturally delighted, therefore,
when it turned out that such widespread melting is anything but
unprecedented. It happened most recently in 1889, and it
happens, on average, every 150 years or so. This summer’s
surface melt has very likely been influenced by global warming,
but it might have happened anyway. The same goes for the heat
waves that have pummeled large pa