America's Heartland, Warmest February
By Sharon Begley
NEW YORK, March 5 (Reuters) - When at least 80 tornadoes rampaged
across the United States, from the Midwest to the Gulf of Mexico, last
Friday, it was more than is typically observed during the entire month
of March, tracking firm AccuWeather.com reported on Monday.
According to some climate scientists, such earlier-than-normal
outbreaks of tornadoes, which typically peak in the spring, will
become the norm as the planet warms.
"As spring moves up a week or two, tornado season will start in
February instead of waiting for April," said climatologist Kevin
Trenberth of the National Center for Atmospheric Research.
Whether climate change will also affect the frequency or severity of
tornadoes, however, remains very much an open question, and one that
has received surprisingly little study.
"There are only a handful of papers, even to this day," said
atmospheric scientist Robert Trapp of Purdue University, who led a
pioneering 2007 study of tornadoes and climate change.
"Some of us think we should be paying more attention to it," said
atmospheric physicist Anthony Del Genio of the Goddard Institute for
Space Studies, part of NASA.
The scientific challenge is this: the two conditions necessary to
spawn a twister are expected to be affected in opposite ways. A warmer
climate will likely boost the intensity of thunderstorms but could
dampen wind shear, the increase of wind speed at higher altitudes,
researchers say.
Tomorrow's thunderstorms will pack a bigger wallop, but may strike
less frequently than they have historically, explained Del Genio.
"As we go to a warmer atmosphere, storms - which transfer energy from
one region to another - somehow figure out how to do that more
efficiently," he said. As a result, thunderstorms transfer more energy
per outbreak, and so have to make such transfers less often.
In a 2011 paper, Del Genio calculated that, "especially in the central
and eastern United States, we can expect a few more days per month
with conditions favorable to severe thunderstorm occurrence" by the
latter part of this century if the global climate grows warmer.
Indeed, the world has been experiencing more violent storms since
1970, the Intergovernmental Panel on Climate Change reported in its
most recent assessment.
EXTENDING TORNADOES' PATH
Purdue's Trapp and colleagues got a similar result in their 2007
study, which they confirmed in research published in 2009 and 2011.
"The number of days when conditions exist to form tornadoes is
expected to increase" as the world warms, he said.
In addition, they found, regions near the Gulf of Mexico and Atlantic
coasts not normally associated with tornadoes will experience
tornado-making weather more frequently. They projected a doubling in
the number of days with such conditions in Atlanta and New York City,
for instance.
More powerful thunderstorms would be expected to produce more
tornadoes, but wind shear could prove a mitigating factor.
Because climate change is not uniform, Del Genio wrote in the 2011
paper, "in the lower troposphere, the temperature difference between
low and high latitudes decreases as the planet warms, creating less
wind shear."
Other scientists are not so sure, and they see a surge in tornadoes
last year as ominous. April 2011 was the most active tornado month on
record, with 753, according to the National Oceanic and Atmospheric
Administration (NOAA), compared to the previous record of 267 in April
1974.
"I have no doubt that there will be many times when wind shear is
plenty strong to create a tornado," said Trenberth.
That is what Trapp's team concluded in their 2007 study. "Over most of
the United States," they wrote, the increase in the power of
thunderstorms will "more than compensate for the relative decreases in
shear."
As a result, "the environment would still be considered favorable for
severe convection" of the kind that creates tornadoes.
From March to May the projected increase in severe storms is "largest
over a 'tornado-alley'-like region extending northward from Texas,"
Trapp found. From June through August, the eastern half of the country
is projected to experience such an increase.
If there are more days in the future when wind shear is too weak to
produce a tornado from a thunderstorm, said Trenberth, then "the
frequency of tornadoes may decrease but the average intensity might
increase. You could have a doozy of an outbreak, and then they could
go away for a while."
On average, about 800 tornados are reported annually in the United
States. About 70 percent are "weak," finds NOAA, with winds less than
110 mph (177 kph) . Just under 29 percent are "strong," with winds
between 110 and 205 mph (177 and 329 kph) . Only 2 percent of all
tornadoes are what NOAA characterizes as "violent," with winds in
excess of 205 mph (329 kph) , but they account for 70 percent of all
twister deaths. (Editing by Michele Gershberg and Sandra Maler)
More:
http://www.huffingtonpost.com/2012/03/06/midwest-tornadoes-record-week_n_1322500.html
--
Together, we can change the world, one mind at a time.
Have a great day,
Tommy
--
Together, we can change the world, one mind at a time.
Have a great day,
Tommy
--
Thanks for being part of "PoliticalForum" at Google Groups.
For options & help see http://groups.google.com/group/PoliticalForum
* Visit our other community at http://www.PoliticalForum.com/
* It's active and moderated. Register and vote in our polls.
* Read the latest breaking news, and more.
No comments:
Post a Comment