Heat Waves to be More Severe, More Frequent and Longer Lasting w/Global Warming
- The article below states that the most severe health impacts from the
Chicago heat wave of 1995 was due to the lack of cooling relief
several nights in a row. I've also read that very high humidity
levels (higher heat indexes) had a lot to do with number of heat-
related deaths from the Chicago 1995 heat wave.
Future Heat Waves: More Severe, More Frequent, Longer Lasting
Anatta, NCAR Media Relations
Jerry Meehl, NCAR
BOULDER--Heat waves in Chicago, Paris, and elsewhere in North America
and Europe will become more intense, more frequent, and longer
lasting in the 21st century, according to a new modeling study by two
scientists at the National Center for Atmospheric Research (NCAR). In
the United States, the increase in heat wave severity will be
greatest in the West and the South. The findings appear in the
August 13 issue of the journal Science.
Gerald Meehl and Claudia Tebaldi, both of NCAR, examined Earth's
future climate using the Parallel Climate Model, developed by NCAR
and the U.S. Department of Energy (DOE). NCAR's primary sponsor, the
National Science Foundation, and the DOE funded the study, with
additional support from NCAR's Weather and Climate Impact
Model results show that an increase in heat-absorbing greenhouse
gases intensifies an unusual atmospheric circulation pattern already
observed during heat waves in Europe and North America. As the
pattern becomes more pronounced, severe heat waves occur in the
Mediterranean region and the southern and western United States.
Other parts of France, Germany, and the Balkans also become more
susceptible to severe heat waves.
"It's the extreme weather and climate events that will have some of
the most severe impacts on human society as the climate changes,"
Heat waves can kill more people in a shorter time than almost any
other climate event. By a measure of excess death reports, 739 people
died as a result of Chicago's heat wave July 14-20, 1995. Fifteen
thousand are estimated to have died from heat in France in August
2003, along with thousands of farm animals.
For the study, Meehl and Tebaldi compared present (1961-1990) and
future (2080-2099) decades to determine how greenhouse gases and
sulfate aerosols might affect future climate in Europe and the United
States, focusing on Paris and Chicago. They assumed little in the way
of policy intervention to slow the buildup of greenhouse gases.
During the Paris and Chicago heat waves, changes in atmospheric
pressure produced clear skies and prolonged hot conditions at the
surface. In the model, similar atmospheric pressure changes are
enhanced during heat waves in both regions as carbon dioxide
accumulates in the atmosphere.
--Heat waves will become more severe
During the Chicago heat wave, the most severe health impacts resulted
from the lack of cooling relief several nights in a row, according to
health experts. In the model, the worst three-day heat waves show a
rise of more than 3 degrees Celsius (5.4 degrees Fahrenheit) in
minimum nighttime temperatures in the western and southern United
States and the Mediterranean region of Europe.
--They will occur more often
The average number of heat waves in the Chicago area increases in the
coming century by 25%, from 1.66 per year to 2.08. In Paris, the
average number increases 31%, from 1.64 per year to 2.15.
--They will last longer
Chicago's present heat waves range from 5.39 to 8.85 days; future
events increase to between 8.5 and 9.24 days. For Paris, present-day
heat waves range from 8.33 to 12.69 days; they stretch to between
11.39 and 17.04 days in future decades.
Opinions, findings, conclusions, or recommendations expressed in this
publication are those of the author(s) and do not necessarily reflect
the views of the National Science Foundation.
Note to Editors: Reporters may obtain the paper, "More intense, more
frequent, and longer lasting heat waves in the 21st century," by
Gerald A. Meehl and Claudia Tebaldi, by calling 1-202-326-6440 or e-
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