If you listened carefully to a National Public Radio report on polar bears yesterday, you might have noticed a little inconsistency. A report said that polar bears are threatened because global warming is causing declining Arctic sea ice (from which bears hunt for seals). But it also said that the bears are “in good shape now” and mentioned one, a healthy bear of record weight, that a researcher described as “a very fat bear for this time of the year . . . his belly almost scraped the ground, so he was a really fat good-looking bear.”

If you’re wondering how thriving bears and declining Arctic sea ice threatening their extinction could go hand-in-hand, you’re thinking straight. Shrinking sea ice and fattening bears aren’t supposed to go together.

Part of the explanation is that Arctic sea ice, which hit its lowest summer extent in 2007, has recovered greatly since then, now nearing the 1979-2000 mean. Its smallest March extent since 1979 e.g., in 2006, was 8.4% below the mean, but this year’s March extent was only 3.75% below.

The notion that Arctic sea ice shrinkage has been caused by global warming is also suspect, for during the years of most rapid shrinkage, Earth was actually cooling rapidly. No wonder “a paper by NASA in 2008 attributed this ice-melt” not to global or even regional warming but “to unusual northbound currents and winds bringing warmth up from the tropics to the Arctic, and a more recent paper says that the summertime Polar winds in 2007/8 had blown much of the sea ice southward into warmer waters, where it melted.”

Finally, Arctic temperatures were warmer in the 1930s and 1940s than since 1979, and ice extent shrank as much or more then (with the Northwest Passage opening several times to shipping), but the polar bears survived. They also survived when there was much less ice 6,000 to 7,000 years ago. And their number seems to have been growing , not shrinking, in recent years.