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August
30, 2007
NASA STUDY PREDICTS MORE SEVERE
STORMS
WITH GLOBAL WARMING
NASA scientists have developed a new climate
model that indicates
that the most violent severe storms and tornadoes may become more
common as
Earth’s climate warms.
Previous climate model studies have shown that heavy rainstorms will be
more
common in a warmer climate, but few global models have attempted to
simulate
the strength of updrafts in these storms. The model developed at
NASA’s Goddard
Institute for Space Studies by researchers Tony Del Genio, Mao-Sung
Yao, and
Jeff Jonas is the first to successfully simulate the observed
difference in
strength between land and ocean storms and is the first to estimate how
the
strength will change in a warming climate, including “severe
thunderstorms”
that also occur with significant wind shear and produce damaging winds
at the
ground. This information can be derived from the temperatures and
humidities
predicted by a climate computer model, according to the new study
published on
August 17 in the American Geophysical Union’s Geophysical
Research Letters. It
predicts that in a warmer climate, stronger and more severe storms can
be
expected, but with fewer storms overall.
Global computer models represent weather and climate over regions
several
hundred miles wide. The models do not directly simulate thunderstorms
and
lightning. Instead, they evaluate when conditions are conducive to the
outbreak
of storms of varying strengths. This model first was tested against
current
climate conditions. It was found to represent major known global storm
features
including the prevalence of lightning over tropical continents such as
Africa
and, to a lesser extent, the Amazon Basin, and
the near
absence of lightning in oceanic storms.
The model then was applied to a hypothetical future climate with double
the
current carbon dioxide level and a surface that is an average of 5
degrees
Fahrenheit warmer than the current climate. The study found that
continents
warm more than oceans and that the altitude at which lightning forms
rises to a
level where the storms are usually more vigorous.
These effects combine to cause more of the continental storms that form
in the
warmer climate to resemble the strongest storms we currently
experience.
Lightning produced by strong storms often ignites wildfires in dry
areas.
Researchers have predicted that some regions would have less humid air
in a
warmer climate and be more prone to wildfires as a result. However,
drier
conditions produce fewer storms. "These findings may seem to imply that
fewer storms in the future will be good news for disastrous western U.S. wildfires," said
Tony Del Genio, lead
author of the study and a scientist at NASA’s Goddard
Institute for Space
Studies, New
York.
"But drier conditions near the ground combined with higher lightning
flash
rates per storm may end up intensifying wildfire damage instead."
The central and eastern areas of the United States
are especially prone
to severe storms and thunderstorms that arise when strong updrafts
combine with
horizontal winds that become stronger at higher altitudes. This
combination
produces damaging horizontal and vertical winds and is a major source
of
weather-related casualties. In the warmer climate simulation there is a
small
class of the most extreme storms with both strong updrafts and strong
horizontal winds at higher levels that occur more often, and thus the
model
suggests that the most violent severe storms and tornadoes may become
more
common with warming.
The prediction of stronger continental storms and more lightning in a
warmer
climate is a natural consequence of the tendency of land surfaces to
warm more
than oceans and for the freezing level to rise with warming to an
altitude
where lightning-producing updrafts are stronger. These features of
global
warming are common to all models, but this is the first climate model
to
explore the ramifications of the warming for thunderstorms.
The Goddard Institute for Space Studies is a leading center in the
study of
Earth’s past, present and future climates.
##
Contact:
Leslie
McCarthy
Goddard Institute for Space Studies
212-678-5507
lnolan@giss.nasa.gov
This text is derived from:
http://www.nasa.gov/centers/goddard/news/topstory/2007/moist_convection.html
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