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In this file photo, construction worker Chester Gibson wipes sweat from his face on a hot day in Houston, Tex.
Hot and muggy weather over the past few decades has led to about a 10 percent drop in the physiological capacity of people to do their work safely and those drops will be even greater as the climate continues to warm, a new study finds.
People may continue to work in the hot and muggy conditions, "but their misery will increase while they are productive," John Dunne, a research oceanographer with the National Oceanic and Atmospheric Administration in Princeton, N.J., told NBC News.
Dunne is the lead author of the study, which addresses the impact of rising humidity associated with global warming on the capacity of people to safely do their jobs — from toiling in agricultural fields to crunching numbers at a desk.
The federal government maintains industrial and military guidelines that call for laborers to take breaks when conditions on a widely-used heat-stress index cross certain thresholds.
"Black flag" conditions in military parlance, for example, correspond to a reading of greater than 90 degrees on the wet bulb global temperature index. Under those conditions, all non-mission critical physical training and strenuous exercise is suspended.
Dunne and colleagues combined historical analysis of the heat-stress index and model projections of future climate with the worker safety guidelines.
They found that environmental heat stress has reduced worker capacity over the past few decades to 90 percent during the hottest months of the year and project a further reduction to 80 percent in peak months by 2050 and less than 40 percent by 2200.
The highest plausible warming scenario modeled will expose “mid-latitude regions such as the US east of the Rockies to environmental heat stress experienced only by the most extremely hot regions of the present day” such as parts of India, Dunne and colleagues write in a paper published today in Nature Climate Change.
Dunne noted the findings come with several caveats. For example, uncertainty remains over how much the climate will warm in coming decades and how people will adapt their lifestyles to accommodate warmer conditions. It’s possible that agricultural work will shift to higher latitudes, for example, and afternoon siestas could be routine in mid-latitudes.
"The thing I like about this metric," noted Dunne, "is it is something that people have adapted their life to across the globe in the present day."
John Roach is a contributing writer for NBC News. To learn more about him, check out his website.