News•February 24, 2013

Climate Change Is Cutting Humans’ Work Capacity

By Lauren Morello

It’s not just the heat, it’s the humidity that gets you.

That’s the conclusion of a new study that finds climate change has reduced humanity’s ability to work by making the planet hotter and muggier.

That one-two punch has already cut the world’s working capacity by 10 percent since humans began burning large amounts of oil, gas, coal and other fossil fuels at the start of the Industrial Revolution, found the analysis, which was published Sunday in the journal Nature Climate Change.

By 2200, heat and increased humidity would hamper people’s ability to work to less than 40 percent of their capacity.

Researchers at the National Oceanic and Atmospheric Administration predict that dive will continue, reshaping daily life in the most populated areas of the planet as climate change intensifies.

By 2050, a combination of rising heat and humidity is likely to cut the world’s labor capacity to 80 percent during summer months — twice the effect observed today.

“The planet will start experiencing heat stress unlike anything experienced today,” said study co-author Ron Stouffer, a climate modeler at NOAA’s Geophysical Fluid Dynamics Laboratory. “The world is entering a very different environment, and the impact of that on labor will be significant.”

Those calculations don’t take into effect the relief offered by air conditioning. They do assume people will take other measures to beat the heat — working or exercising in early morning, early evening or even nighttime, seeking shade and wearing clothing that helps maximize their ability to stay cool.

The analysis is based on the effect of changes in “wet bulb” temperatures.

Unlike the air temperatures most people are familiar with, wet bulb readings account for humidity and wind speed as well as temperature. That’s important because high humidity can make it harder for people to cool themselves by sweating, increasing the likelihood of heat-related illness.

To determine whether climate change had already affected people’s ability to work the new study’s authors calculated wet-bulb temperature readings for today’s climate and compared them to pre-industrial conditions.

Then, using a NOAA climate model, the researchers projected how conditions would change over the next two centuries for people who are active in environments without air conditioning.

By mid-century, they found, climate change is poised to cut work capacity during summer months by 20 percent, compared to pre-industrial levels — twice the effect observed in today’s world.

Credit: World Preservation Foundation

Fifty years later, in 2100, that effect would double again if the world does not find a way to reduce its carbon dioxide output. Humans’ work capacity would drop to just 63 percent during the hottest months of the year.

Zoom another 100 years forward, to 2200, and the Earth’s average temperature would be 11°F hotter than it was before the Industrial Revolution. Scorching heat and increased humidity would slash people’s ability to work to less than 40 percent of their full capacity each summer.

Across much of the U.S., a nasty combination of heat and humidity would create “heat stress beyond what is experienced in the world today,” said the study’s lead author, John Dunne, a NOAA research oceanographer. “This illustrates the stark consequences of extreme warming for the tropics and the mid-latitudes, where most people live.”

In the Lower Mississippi Valley, conditions would prevent any safe level of sustained work, the new study found. That’s equivalent to the most severe rating — “black flag” — on the scale the U.S. military uses to determine safe levels of activity for its troops.

In Washington, D.C., conditions would reach the “yellow flag” level on the military scale, the point at which outdoor activities and work “should be curtailed as much as possible,” according to one Navy handout.

Industrial guidelines for preventing heat stress under those conditions recommend working “25 percent on, 75 percent off” — resting three times as long a period as a person labors each hour.

Finding a way to slash the world’s carbon dioxide output later this century would blunt climate’s impact on work capacity but not eliminate the effect, the researchers found.

If society can stabilize the level of CO2 in the atmosphere by early next century, and hold warming to just less than 3°F by 2100, Earth’s tropics and mid-latitudes would experience months each year of “extreme heat stress,” the study said.

The combined heat and humidity in Washington, D.C., would be more stressful than conditions in today’s New Orleans. New Orleans, in turn, would experience more heat stress than Bahrain does now. And in Bahrain — an island in the Persian Gulf where temperatures already hit 120°F in summer months — heat stress would creep close to the limit that humans can endure for more than a few hours at a time.

Even under that “better case” emissions scenario, Washington, D.C., and New York City would both “well exceed” the heat stress of present-day Bahrain by 2200, the researchers found.

Experts who were not involved with the research praised it as a solid, sobering analysis.

“This is an excellent study that draws upon existing work on heat stress and combines it with climate model projections of the future to bring home the point that ‘global warming’ means, among other things, that it will get quite hot and wet in many places,” said Matthew Huber, a climatologist at Purdue University.

Huber, who has published work examining the limits of humans’ ability to tolerate high heat and humidity, said the study suggests that economic models used to project the economic toll of climate change may be underestimating its financial impacts.

Another researcher who has looked specifically at the effects of climate change on occupational health and productivity, Ingvar Holmér of the University of Lund, Sweden, noted that the wet-bulb globe temperature index the new study's authors used was developed in the U.S. and Europe and has not been extensively tested in Africa and Asia. But it is likely the best of all available options, said Holmer, who called the new study well-written.

The wet-bulb index “forms a reasonably good basis for this type of calculation because it is well-known and simple,” he said.

Thomas Bernard, a professor of public health at the University of South Florida, said it’s clear that “you’re going to have a loss of productivity as the temperatures go up.”

“That’s a good, valid, kind of irrefutable message,” said Bernard, who studies heat stress management. “If (the study’s authors) want to argue that there is an economic cost, I think they’re on strong ground.”