NBC Nightly News (1/12/13) asked a serious question the other night–and then gave a not-so-serious answer.
Anchor Lester Holt remarked at the top of the broadcast:
Strange winter. Why it is so cold where it should be warm, and so warm where it should be cold? What is going on with all this extreme weather?
To answer the question, he turned to correspondent Kristen Dahlgren, who went to the Weather Channel's Greg Postel, who gave this explanation:
A very strong dip in the jet stream has placed itself over the western part of the country and that's allowed some very cold air from Canada to move southward.
That's true as far as it goes–but it didn't go any farther. Specifically, it never mentioned climate change–something that has been linked to disruptions in the jet stream's traditional path. As the blog ClimateSight (12/19/12) explained:
The jet stream isn't straight, though; it's rather wavy in the north-south direction, with peaks and troughs…. Sometimes a large peak or trough will hang around for weeks on end, held in place by certain air pressure patterns. This phenomenon is known as "blocking," and is often associated with extreme weather….
As climate change adds more energy to the atmosphere, it would be naive to expect all the wind currents to stay exactly the same. Predicting the changes is a complicated business, but a recent study by Jennifer Francis and Stephen Vavrus made headway on the polar jet stream. Using North American and North Atlantic atmospheric reanalyses (models forced with observations rather than a spin-up) from 1979-2010, they found that Arctic amplification–the faster rate at which the Arctic warms, compared to the rest of the world–makes the jet stream slower and wavier. As a result, blocking events become more likely.
Instead of giving this background, Dahlgren merely marveled: "Talk about upside-down weather." Let's talk, rather, about journalists who are failing to acknowledged global climate changes when they're staring them in the face.