Scientists: Killer Heat Waves Tied to Global Warming

In Fresno, the morgue is full of victims from a California heat wave. A combination of heat and power outages killed a dozen people in Missouri. And in parts of Europe, temperatures are hotter than in 2003 when a heat wave killed 35,000 people.

Get used to it.

— For the next week, much of the nation should expect more "extreme heat," the National Weather Service predicts.

— In the month of August, most of the United States will see "above normal temperatures," forecasters say.

— For the long-term future, the world will see more and worse killer heat waves because of global warming, scientists say.

The July burst of killer heat waves around the world can't be specifically blamed on global warming. And they aren't the worst ever — they still can't quite hold a melting candle to the scorching heat of America's 1930s Dust Bowl. But the trend is pointed in that direction, experts say.

Heat waves and global warming "are very strongly" connected, said Kevin Trenberth, climate analysis branch chief at the National Center for Atmospheric Research in Boulder, Colo.

The immediate cause of the California heat wave — and other heat waves — is day-to-day weather, he said.

A persistent high pressure system in the upper atmosphere prevents cooler jetstream air, from making it into the West, said National Weather Service meteorologist Dennis Feltgen.

"You can't tie global warming into one single event," he said.

But what global warming has done is make the nights warmer in general and the days drier, which help turn merely uncomfortably hot days into killer heat waves, Trenberth said.

Much of global warming science concentrates on average monthly and yearly temperatures, but recent studies in the past five years show that climate change is at its most dangerous during extreme events, such as high temperatures, droughts and flooding, he said.

"These [heat] events always occur. What global warming does is push it up another notch," Trenberth said.

And the computer models show that soon, we'll get many more — and hotter — heat waves that will leave the old Dust Bowl records of the 1930s in the dust, said Ken Kunkel, director of the Center for Atmospheric Sciences at the Illinois State Water Survey.

The way to really judge will be when scientists look back a decade from now, not at a single heat wave, but at the frequency and extremes of all of them, said Mike Wallace, a professor of atmospheric sciences at the University of Washington in Seattle.

That's when scientists will likely see a statistically significant increase in heat waves and their severity, he said. In fact, he said, that can be seen a bit now.

In the past 25 years most of the world, has seen summer nights getting much warmer with far less evening heat relief, according to a study published earlier this year in the peer-reviewed Journal of Geophysical Research.

Another study this year by the Climate Research Unit in at the University of East Anglia in Norwich, England, concluded that European summer heat waves "have increased in frequency at most stations since 1880" and will continue to increase with man-made global warming.

In the current U.S. wave, more than 150 people have died. Feltgen ticks off a few statistics from the hardest-hit state, California:

"One hundred twenty-six degrees in Death Valley last week; Sacramento had 11 days at or above 100 degrees, their old record was nine. We're seeing some impressive records out there to be sure and unfortunately this is taking a human toll."

George Luber, an epidemiologist who studies heat wave deaths for the U.S. Centers for Disease Control and Prevention, says the current situation is on track to be "the most active one that I can recall" in terms of heat deaths.

A new analysis by Luber this week shows that between 1999 and 2003, the United States averaged nearly 900 heat-related deaths each year. This year, with 132 reported in central California alone, could be worse, he said.

"It's never been like this in my years here," Fresno County Coroner Loralee Cervantes said this week. "This is really tragic."

One way heat waves cause so much death is that people — especially the elderly staying in their homes — aren't able to get cool at night when temperatures remain high after sundown.

"The deaths are really related in urban areas to nighttime temperatures," said Stan Chagnon, a retired Illinois meteorology professor who did some of the earliest research on killer heat waves. "The mixture of moisture in the air (which other experts say acts as a blanket trapping heat) and high nighttime temperatures, a lot of people say, is really a killer."

Luber, the CDC doctor, says a body needs at least three hours of cooling — preferably by air conditioning — to survive excessive heat.

Cities are worse for heat deaths because they remain hotter at night from the "heat island effect," Chagnon said.

And older northern cities — where many homes lack air conditioning — are worse off than Sunbelt cities where most people have cooling.

"Our society is becoming ever more vulnerable to climate due to growth, where we live," Chagnon said.

There is some good news in all this. Cities, such as St. Louis, New York and Philadelphia, have learned how to prevent heat deaths. And as heat waves worsen, the U.S. rate of heat deaths per population has not risen, because cities have created cooling centers and systems to check on the vulnerable elderly and poor, the CDC's Luber said.

"Everything with heat death can be prevented," Luber said. "Maybe we prevented a whole lot more deaths than we realized."