“People may very well remember this as a year of
extreme weather and climate.” —JESSICA BLUNDEN
Probability of some droughts, heat waves now much greater
efforts to get near real-time assessments
of climate’s role in extreme weather
events, says climatologist Thomas
Peterson of the National Climatic Data
Center, in Asheville, N.C.
Recent extreme weather attributed
to human-caused climate warming
For years, he says, climate scientists have argued that although global
warming can increase the frequency
of extreme weather, they couldn’t pin
any particular event on human-caused
climate change. That appears to be
changing, Peterson and his colleagues
argue.
Using a developing field known as
“attribution science,” researchers are
beginning to apply massive computing
capacity to explore how global temperatures, surface reflectivity and moisture
patterns can affect the odds of localized
extreme weather events.
In 2011, droughts beyond Africa and
Texas brought billions of dollars in
crop losses, Blunden says. The North
Atlantic saw above-average hurricane activity ( 19 named storms, compared with an average of 12), and seven
separate U.S. tornado outbreaks that
each wreaked more than $1 billion in
damage.
Polar regions racked up their own
extremes, says Martin Jeffries of the
University of Alaska Fairbanks. Barrow,
Alaska, sustained a record 86 days in a
row when the minimum air temperature
failed to dip below freezing.
Understanding global warming’s role
in extreme events extends well beyond
blaming rights. Peterson notes that
water managers may need to change
policies if evidence begins pointing to
persistent changes in the recurrence
rates and lengths of droughts or the
frequency of heavy rains.
Right now, linking these events is
difficult, usually works only for events
lasting longer than a month and can
take a year to complete. Peterson’s team
hopes to see the science mature to the
point that assessments might be turned
around more quickly and to tackle
events lasting mere days. s
© DAVID WOO/DALLAS MORNING NEWS/CORBIS
By Janet Raloff
Texans sweltered through the hottest,
driest spring and summer on record last
year. Much of the blame can be attributed to a recurring climate pattern
known as La Niña, which emerges every
few years as surface waters chill in the
eastern equatorial Pacific. But Earth’s
steadily warming climate contributed
as well, a new analysis concludes.
Since the 1960s, the likelihood of Texas
seeing extremely hot, dry weather in a
La Niña year has mushroomed 20-fold
due to human-induced global warming,
David Rupp of Oregon State University
in Corvallis and his colleagues calculate.
The researchers were one team
among six international groups
probing climate’s link to extreme events
in late 2010 through 2011. The collected
findings appear July 10 in the Bulletin of
the American Meteorological Society.
“People may very well remember
this as a year of extreme weather and
climate,” says Jessica Blunden of the
National Climatic Data Center and an
editor of State of the Climate in 2011, a
report published as a supplement to the
July 10 Bulletin of the American Meteorological Society.
Severe food shortages gripped the
Horn of Africa last year after drought
left the land parched from winter 2010
through the following spring. La Niña
played a role there, too. And computer
analyses of global climate conditions
since 1979 find that a recent warming of surface waters in the Indian
and Pacific oceans has destabilized
La Niña weather patterns. Chris Funk
of the U.S. Geological Survey in Santa
Barbara, Calif., concludes that this
process probably intensified 2011’s
drought in East Africa.
Other teams pointed to global warming as a likely contributor to excessive
heat in central Europe last summer and
to unusually balmy temperatures in
central England in November 2011. In
the British case, that kind of heat could
be expected to recur every 20 years
now — a 62-fold increase over the 1960s.
Yet global warming can’t be blamed
for all monster weather. Unprecedented
flooding that submerged large tracts
of northern Thailand, including its
capital, for up to two months last year
resulted from rainfall at an intensity
the region had encountered before. But
water management practices and heavy
industrialization of a floodplain slowed
drainage last year.
These new analyses are pioneering
Benbrook Lake near Fort Worth, Texas,
dried up last year during the state’s
warmest August on record. A new
analysis links global warming with
increases in extreme weather.
