(Eric Berger in New York Times) It’s late October, when seas
outside the tropics are supposed to be falling into a winter chill. So what is
a “super” hurricane doing approaching the northeastern United States and
strengthening as it’s crossing the mid-latitude waters of the Atlantic Ocean?
This is a fair question. It’s also reasonable to
ask whether this storm is a product of climate change, that a warmer world will
produce more “super” storms.
Hurricane blame game to begin soon.
Certainly that’s the point of view espoused by some
“Folks, this storm is exactly the sort of thing
climate scientists have been worried about for years,"
“Global warming is putting hurricanes on steroids
and we’re beginning to see the effects.”
Expect to hear more of the same in the wake of
Sandy’s destruction. After hurricanes the natural reaction of humans is to find
someone to blame — be it forecasters, government or in a more nebulous sense,
However the science of climate change and
hurricanes does not support this conclusion. Even before Hurricane Katrina
ravaged the Gulf Coast in 2005 scientists have been hard at work trying to
understand how increasing levels of carbon dioxide, and rising temperatures,
will affect hurricane activity.
At first blush, it would seem that warmer seas
would fuel more and stronger hurricanes, because tropical storms typically form
and intensify when waters are at their peak temperatures. But in this case,
nature is more complicated, and while warmer oceans may be more favorable in a
warmer world, other factors appear to temper hurricane activity.
After a lot of back and forth in the scientific
community, an important paper (see abstract) came out in 2010
in Nature Geoscience. It was authored by a working group
established by the World Meteorological Organization to study the effect of
climate change on hurricane activity. Its members included scientists who
are both very bullish on climate change increasing damage from hurricanes
(i.e. Greg Holland) and scientists who are
not (Chris Landsea).
Here were the paper’s main conclusions:
studying past and present hurricane data they did not conclusively find
any detectable human influence on hurricane activity.
indicate more likely than not an increase in the numbers of the more
intense hurricanes globally, perhaps 2 to 11 percent by 2100.
also found increased evidence that, globally, the number of tropical
storms is likely to decrease by 6 to 34 percent by 2100.
is some evidence that hurricanes will produce more rainfall in a warmer
For more of a discussion on the Nature Geoscience
paper, see this blog entry I did at the time.
But what about Sandy in particular? It is, in part,
being fueled by water temperatures that are several degrees higher than normal.
The image below shows Sandy traversing an area where sea surface temperatures
are 2 to 4 degrees Fahrenheit above normal.
these temperatures are a fraction of a degree warmer due to climate change, and
perhaps not. North Atlantic sea surface temperatures have generally been above
normal since 1995 due to a natural feature called the Atlantic Multidecadal Oscillation.
the recent strengthening of Hurricane Sandy is attributable, in large measure,
to baroclinic forcing. This is a technical term that represents the collision
of very warm air (Sandy) with very cold air (a strong cold front moving
southeast from Canada). The collision of these air masses is providing energy
other words, cold air is in some sense allowing Sandy to strengthen. Cold air.
bottom line is that climate change is unquestionably having an effect on the
weather around us by raising the average temperature of the planet. This is producing
warmer temperatures and very likely increasing the magnitude of droughts.
However, it is a big stretch to go from there to blaming Sandy on climate
change. It’s a stretch that is just not supported by science at this time.
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