Reduced Greenhouse Gas Emissions Required To Avoid Dangerous Increases In Heat Stress
Pastor Dale Morgan
Reduced Greenhouse Gas Emissions Required To Avoid Dangerous Increases
In Heat Stress
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This image represents intensification of dangerous heat stress in the
21st century. The color contours show the expected intensification of
dangerous heat index days given accelerating increases in greenhouse gas
concentrations. (Purdue University image/Diffenbaugh Laboratory)
by Elizabeth K. Gardner
West Lafayette IN (SPX) Jun 15, 2007
A study led by a Purdue University researcher projects a 200 percent to
500 percent increase in the number of dangerously hot days in the
Mediterranean by the end of the 21st century if the current rate of
greenhouse gas emissions continues. The study found France would be
subjected to the largest projected increase of high-temperature extremes.
The study also showed a reduction in greenhouse gas emissions could
reduce the intensification of dangerously hot days projected in the
scenario by up to 50 percent.
"Rare events today, like the 2003 heat wave in Europe, will become much
more common as greenhouse gas concentrations increase," said Noah
Diffenbaugh, the Purdue assistant professor of earth and atmospheric
sciences who led the study. "The frequency at which that scale of event
occurs at high greenhouse gas concentrations is staggering. Rare events
become the norm, and the extreme events of the future are unprecedented
in their severity."
A 2003 heat wave led to 15,000 deaths in France and almost 3,000 in
Italy. The researchers found that global warming causes summer
temperatures to dramatically exceed the range that was correlated with
the increased number of deaths.
"The thresholds of the 2003 event are substantially exceeded in the
future in both of our research scenarios," said Diffenbaugh, who is a
member of Purdue's Climate Change Research Center. "This research is
about understanding the response to different emissions levels. We find
that decreases in greenhouse gas emissions greatly reduce the impact,
but we see negative effects even with reduced emissions. Technological
and behavioral changes that are made now will have a big influence on
what actually happens in the future."
In addition to the human health risks, extremely high temperatures could
impact the economy of this region, which includes metropolitan areas
such as Rome, Paris and Barcelona, said Jeremy Pal, co-researcher and
associate professor of civil and environmental engineering at Loyola
Marymount University.
The study covered the entire Mediterranean area, which includes 21
countries in Europe, Africa and Asia. Major cities covered in the study
include: Prague, Zurich, Bucharest, Athens, Istanbul, Tel Aviv, Cairo,
Algiers and Casablanca.
"When high temperature extremes increase, it could have significant
negative impacts on human health, water resources, agriculture and
energy demand," Pal said.
The results of the study, which originated at the International Centre
for Theoretical Physics in Trieste, Italy, will be published in the
Friday (June 15) issue of Geophysical Research Letters.
In addition to Diffenbaugh and Pal, Filippo Giorgi of the International
Centre for Theoretical Physics and Xuejie Gao of the National Climate
Center in Beijing are co-authors of the paper. The researchers used a
supercomputer in the National Climate Center in Beijing to run the
climate model.
The model offers a resolution of 20 kilometers, about 12.5 miles, and is
believed to have the highest spatial resolution available for the
Mediterranean region. Much like increased resolution in a photo makes a
clearer picture and allows one to zoom in without blurring the image,
the powerful resolution of the climate model allows researchers to
gather detailed information about particular areas.
Giorgi, who is head of the Earth System Physics Section of the
International Centre for Theoretical Physics, said the Mediterranean is
of interest because it is one of the most susceptible areas to climate
changes - both climatically and socially.
"In the global warming scenario, there is more warming and drying in the
Mediterranean than in other regions of the world, which makes the
Mediterranean a climate change 'hotspot,'" Giorgi said. "The
Mediterranean also is a very vulnerable region to climate change in
terms of the impacts to the way of life of those who live there."
The researchers found that this warming and reduced precipitation
contribute to a preferential warming of the hottest days of the year.
"We found that the hottest days of the year, or the 'hot tail,' warm
more than the typical summer days warm," Diffenbaugh said. "One might
expect that an average warming of four degrees would equate to each day
warming by four degrees, but in fact the hottest days warm quite a bit
more."
This is due, in large part, to a surface moisture feedback. The surface
gets dryer as it gets hotter and the dry soil leads to less moisture in
the area and less evaporative cooling. The locations of intensified
warming on hottest days of the year matched the locations where surface
drying occurred, Diffenbaugh said.
With the projected shift to more severe temperatures, the daily
temperatures currently found in the hottest two weeks of the summer
instead are found in the coldest two weeks of the summer in the future
climate scenario, Diffenbaugh said.
"The hottest temperatures we are used to experiencing will become the
normal temperatures of the summer, and the hot periods will be
magnified," Diffenbaugh said. "Take Paris: If we look at the
temperatures that occurred there during the heat wave in 2003, when
15,000 people died, those temperatures are exceeded a couple dozen times
every year in the future projection. That means that severe heat waves,
such as those rare events that have occurred in the past couple of
years, are likely to become far more common."
The study used the National Weather Service Heat Index in the analysis
of the heat stress response to increasing greenhouse gas concentrations.
The researchers found that areas most likely to face substantial
increases in the dangerous heat index were concentrated largely in
coastal areas.
"Coastal regions were more affected than inland regions, which is of
particular importance because many large cities in the Mediterranean are
on the coast," Giorgi said. "This is the first time this amplification
signal over coastal areas could be seen and quantified. Coastal regions
are particularly vulnerable because they will likely be affected by
other important climate change related stresses, such as a rising sea
level."
Diffenbaugh said without the high resolution of the climate model, the
researchers would not have been able to identify the coastal effects.
"This underscores the importance of advancing our technology and
examining a number of scenarios in great detail," he said. "If we want
to quantify the risks associated with climate change, it is critical to
understand the local and regional impacts as well as the global impacts."
For the study's standard future scenario, the research group used a
commonly accepted emissions scenario from the Intergovernmental Panel on
Climate Change that assumes greenhouse gas emissions continue to
increase exponentially. The reduced emissions scenario incorporated a
reduction in population growth and greater environmental concern,
Diffenbaugh said.
The researchers are currently using the high-resolution model to further
evaluate the effects that increased temperatures and surface drying
could have on agriculture and energy and water resources.
This research was funded by the Italy-USA collaborative agreement on
climate change research and in part by the National Science Foundation.
The Purdue Climate Change Research Center is affiliated with Purdue's
Discovery Park. The center promotes and organizes research and education
on global climate change and studies its impact on agriculture, natural
ecosystems and society. It was established in 2004 to support Purdue in
research and education on regional scale climate change, its impacts and
mitigation, and adaptation strategies. The center serves as a hub for a
range of activities beyond scientific research, including teaching,
public education and the development of public policy recommendations.