64 ASTRONOMY • DECEMBER 2019
FOR YOUR CONSIDERATION
If Earth were the
same temperature
everywhere, our
lives would be pretty boring.
Actually, they would be more
than boring; they would be
impossible. Thank goodness
that isn’t the case. Differences
in the directness of sunlight
at different latitudes and the
high albedo of ice as com-
pared to land and open ocean
mean that equatorial regions soak up a lot more heat than
polar regions. And that thermal gradient is what keeps
things interesting.
The basics of how temperature differences stir things
up are straightforward. Warm air near the equator rises,
then at high altitudes spreads out toward the poles. In the
meantime at lower altitudes, cooler air moves toward the
equator to replace the rising warm air. The opposite hap-
pens at the poles. High-altitude air carrying extra ther-
mal energy moves toward the ground, heating things up,
while cold ground-level air moves toward lower latitudes.
Coriolis effects due to Earth’s rotation break
the system into equatorial, midlatitude, and
polar convective cells separated by high-
altitude jet streams.
Without that global thermal conveyor
belt, the poles would be about 45 degrees
Fahrenheit (25 degrees Celsius) cooler, and
the equator 25 F (15 C) warmer than each is
today. This is the engine that drives Earth’s
climate and weather.
So, what would happen were the differ-
ence between the poles and the equator to lessen for
some reason? Needless to say, things would change, but
how? Again, the basics aren’t hard to grasp. A fast-
spinning top is stable, but as it slows, it wobbles. A hur-
ricane with a very low central pressure has a tight, stable
structure. But as the pressure difference between inside
and outside the storm weakens, circulation becomes
sloppy and unstable.
The same thing applies to Earth’s atmosphere as a
whole. Just like a hurricane coming apart as the central
pressure increases, increasing the temperature of the
poles relative to the equator could easily destabilize
global circulation. Mucking with that balance isn’ttickling Earth’s climate system. It is kicking it squarely
in the posterior.
The thing is, that’s exactly what we’re doing.
Atmospheric carbon dioxide and other gases allow vis-
ible sunlight in but ref lect infrared radiation back into
space. Unsurprisingly, thickening Earth’s atmospheric
blanket heats things up. But that heating isn’t uniform.
The poles are much more affected by greenhouse gases
than is the equator. Melting sea ice adds insult to ther-
mal injury.
As expected (and predicted), as global warming has
reduced the thermal imbalance between poles and the
equator, circulation around the poles has gotten a lot
more wobbly. In some places, the northern polar jet
steam can go way to the south, bringing cold polar air
with it. In other places, it can go way to the north, draw-
ing hot tropical air toward the poles. Those big excur-
sions are called Rossby waves.
Common, fast-moving Rossby waves carry storm
systems from west to east. But the until recently uncom-
mon, slow-moving Rossby waves I’m talking about are a
different beast. These waves get stuck doing what they
do in the same spot, sometimes for weeks on end.
The things that they do are pretty funky, and can get
extreme. For example, the polar jet dipped all the way
down into Arizona in late spring. Snow fell in Flagstaff,
and in Phoenix temperatures 20 F (10 C) below normal
had us wondering if it was time to pull our sweaters back
out. At the same time, the stalled jet stream
pulled humidity from an overly warm Gulf
of Mexico and dropped it on the U.S. Plains,
turning Oklahoma into a good approxima-
tion of an inland sea and blasting it with
tornadoes on a daily basis. The show contin-
ued as Alaska “enjoyed” air coming up from
the tropics, pushing Anchorage above 90 F
(32 C) for the first time ever.
Slow-moving Rossby waves are fun in the
northern winter, too. Referred to as the
“polar vortex,” the masses of polar air Rossby waves bring
southward have been pounding the U.S. Northeast with
hellish record-breaking winter storms even as Alaskans
experience what for them amounts to shirtsleeve weather.
Welcome to the new normal. Why did Nero fiddle
while Rome burned? I’m sure it was spectacular to watch,
and at that point what else was he supposed to do? So, is
it bend-over-and-kiss-your-keister-goodbye time for us?
If not, it’s not far off. But hey! At least the physics of cli-
mate change is cool.The fun physics of global cataclysm.
Watching
Rome burn
On May 23, 2019, once-
unusual but now
increasingly common
slow-moving Rossby
waves disrupted
weather patterns in the
Northern Hemisphere.
In North America, this
brought weeks of
unseasonably cool
weather to the
desert Southwest,
unprecedented
flooding and severe
weather fueled by
humidity from an
abnormally warm
Gulf of Mexico to the
Plains, and sweltering,
humid heat to the
Southeast. JEFF HESTERThe things
that Rossby
waves do are
pretty funky,
and can get
extreme.
BY JEFF HESTER
Jeff is a keynote
speaker, coach,
and astrophysicist.
Follow his thoughts
at jeff-hester.comBROWSE THE “FOR YOUR CONSIDERATION”
ARCHIVE AT http://www.Astronomy.com/Hester