WATCHDOG EARTH

Louisville in 2100 could have three months of killer heat waves

This study is the latest to point to heat as a major threat of climate change in the Louisville area in the coming decades

Courier Journal

A tree ordinance is under consideration at Louisville Metro Council.

If Louisville doesn't already have enough science behind its programs to plant more trees and coax cooler roofing and parking lots, new research out of the University of Hawaii offers another sobering look through a climate change crystal ball.

Without curbs on greenhouse gases, Louisville could experience as many as 92 days in 2100 with deadly heat and humidity. That's up from as many as 14 that we might have now, the study led by Camilo Mora, associate professor of geography at the University of Hawaii at Mānoa, found.

We're not alone.

More: Map shows 'worst-case' flooding from contaminated ash pond in Louisville

Speical report: Our changing planet

Nearly three out of four people globally will be exposed to deadly heat waves by the end of the century under a business-as-usual approach to carbon gas pollution, according to the study, which was published in Nature Climate Change.

Even if emissions are aggressively reduced, the percentage of the world’s human population affected is expected to reach 48 percent, the researchers found.

“We are running out of choices for the future,” Mora said in a news release. “ Many people around the world are already paying the ultimate price of heat waves, and while models suggest that this is likely to continue, it could be much worse if emissions are not considerably reduced."

Humans can only function within a narrow range of core body temperatures around 98.6 degrees, she said. "Heat waves pose a considerable risk to human life because hot weather, aggravated with high humidity, can raise body temperature, leading to life-threatening conditions.”

The researchers made their work available on an interactive website that allows people to look at different heat-wave scenarios over the next eight decades. If emissions of heat-trapping gases such as carbon dioxide or methane aren't cut back, Louisville could experience 43 days of potentially deadly heat by 2050, just 33 years away.

With a moderate cut back, those numbers could drop to 23 potentially deadly days in 2050 and 45 days in 2100. Strong mitigation further pare potentially deadly days to 14.

Some people may be saying: "They can't even get the weather forecast right for a next week, so how can anyone make a heat wave forecast decades out? That's not what this research does, however. It's not a weather forecast.

The researchers found more than 1,900 cases of locations worldwide where high outdoor temperatures have killed people since 1980. They then identified thresholds beyond which temperatures and humidities become deadly, and used computer modeling to get a sense of how heat-trapping pollution might affect heat and public health in the future.

As the Washington Post reported, it is "difficult to say how many more deaths will occur as a result of the extreme heat; that depends on how human societies deal with the problem. Communities could try to lessen the risks by increasing the use of air conditioning or putting better heat warning systems in place."

In Louisville, we're planting at lot of trees, though we still don't have a comprehensive tree protection ordinance. An ordinance that would protect street trees in public rights of ways is winding through Metro Council.

The city also has also begun to offer incentives for cool roofing.

But this study's results are nothing new:

A century of weather records analyzed by Keith Mountain at the Univesity of Louisville showed there likely no escape in Louisville from the fingerprints of climate change, and that going forward, we should see longer smog seasons and more health risks from heat.
A 2009 study by the federal government found that if nothing were done about carbon emissions, temperatures in the Southeast could rise 9 degrees over 70 years.
A 2012 study by the Natural Resources Defense Council estimated that 39 Louisville residents were already dying of heat-related problems. That number, the group concluded, could increase to 257 per year by roughly 2050 and total some 19,000 by 2100 - topping 40 large American cities.
And don't forget how Georgia Tech professor Brian Stone Jr. put Louisville on the map for having the fastest growing urban heat island - you know, that difference between downtown and semi-rural or rural temperatures.

As the New Yorker concluded last year: Louisville "had quietly become the country’s worst example of what meteorologists call the urban heat-island effect, in which dark, paved surfaces absorb solar radiation, raising the temperature of the air around them."

The study out of Hawaii is just another data point in a changing world.

“Climate change has put humanity on a path that will become increasingly dangerous and difficult to reverse if greenhouse gas emissions are not taken much more seriously,” Mora said.

Reporter James Bruggers writes this Watchdog Earth blog. Reach him at 502-582-4645 and at jbruggers@courier-journal.com.