Dr. Holdren:
If you’ve been hearing
that extreme cold spells like the one that we’re having
in the United States now disprove global warming, don’t believe it. The fact is that no
single weather episode can either prove or disprove
global climate change. Climate is the pattern
of weather that we observe geographically
and over the seasons, and it’s described in terms
of averages, variations, and probabilities. But a growing body
of evidence suggests that the kind of extreme cold being experienced by much of the United States
as we speak is a pattern that
we can expect to see with increasing frequency
as global warming continues. And the reason is this: in the warming world
that we’re experiencing, the far north, the Arctic, is warming roughly twice as
rapidly as the mid-latitudes, such as the United States. That means that
the temperature difference between the Arctic and
the mid-latitudes is shrinking, and that temperature
difference is what drives what is called
the circumpolar vortex, which is the great
counterclockwise-swirling mass of cold air that
hovers over the Arctic. As the temperature difference between the Arctic
and the mid-latitudes declines, the polar vortex weakens,
and it becomes wavier. The waviness means that
there can be increased, larger excursions of
cold air southward — that is,
into the mid-latitudes — and, in the other
phase of the wave, increased excursions
of relatively warmer mid-latitude air
into the far north. Computer models tell us that
there are many different factors influencing these patterns. And, as in all science, there
will be continuing debate about exactly what is happening. But I believe the odds
are that we can expect, as a result of global warming, to see more of this pattern of extreme cold
in the mid-latitudes and some extreme warm
in the far north.

The Polar Vortex Explained in 2 Minutes
Tagged on:                                                                                                         

Leave a Reply

Your email address will not be published. Required fields are marked *