msnbc.com staff and news service reports
updated 6/15/2007 3:28:49 PM ET 2007-06-15T19:28:49

Deadly heat waves around the Mediterranean, like those that killed some 18,000 people in 2003, could become the norm this century if current trends in greenhouse emissions continue, researchers reported on Friday.

The number of dangerously hot days in the Mediterranean region that includes parts of Europe, Africa and the Middle East could increase by 200 percent to 500 percent, according to a study in the journal Geophysical Research Letters.

France would have the biggest rise in extreme high temperature days, the study said. Paris would truly sizzle if simulations of the future come to pass, with temperatures that occurred in the French capital during the killer heat wave of 2003 exceeded dozens of times each year.

However, cutting greenhouse gas emissions could make the dangerously hot days as much as 50 percent less intense, the authors said in their analysis of climate simulations extending to the year 2099.

About 15,000 people died in France due to the heat in 2003, and nearly 3,000 died in Italy that same summer.

Rare events can become norm
The researchers found that global warming pushes summer temperatures "dramatically" over the range that correlated with these deaths.

"Rare events today, like the 2003 heat wave in Europe, become much more common as greenhouse gas concentrations increase," researcher Noah Diffenbaugh of Purdue University in Indiana said in a statement. He added that these temperatures "become the norm and the extreme events of the future are unprecedented in their severity."

Today's hottest summer days will be the same temperature as the coolest days of future summers, the analysis by Diffenbaugh and colleagues in California, Italy and China found.

One factor that drives this phenomenon is the fact that extremely hot days warm things up disproportionately more than just moderately hot ones, because the real scorchers dry things out too.

Earth's surface gets dryer as it gets hotter, and the dry soil leads to less moisture in the area and less evaporative cooling. The places where the heat is most intense on the hottest days of the year match the places where surface drying occurs.

Coasts 'particularly vulnerable'
An Italian co-author said the study was especially salient for coastal communities. "This is the first time this amplification signal over coastal areas could be seen and quantified," said Filippo Giorgi of the International Center for Theoretical Physics in Trieste. "Coastal regions are particularly vulnerable because they will likely be affected by other important climate change related stresses, such as a rising sea level."

Many large cities in the Mediterranean region are on the coast, he noted.

Beyond the threat to human life, these forecast soaring temperatures could hurt the Mediterranean region's economy, co-author Jeremy Pal of Loyola Marymount University in Los Angeles said in a statement.

The region stretches to 21 countries that border the Mediterranean Sea, including the cities of Rome, Paris, Barcelona, Algiers, Cairo, Istanbul and Tel Aviv.

Diffenbaugh said technological and behavioral changes now to reduce greenhouse gas emissions could influence what happens in the future, but added, "We see negative effects even with reduced emissions."

Reuters contributed to this report.

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