Although the spectre of climate change typically raises concerns about acute
events such as hurricanes, droughts and heat waves, new research suggests that
global warming may have a much broader chronic impact: the permanent unravelling
of worker productivity due to extreme and enduring heat stress.
The problem: As greenhouse gas emissions rise, so does humidity, say
scientists who support the theory of global warming. This means that today's
steaming hot tropical and mid-latitude regions will increase in size, heat and
discomfort, making it impossible for unprotected outdoor labourers to work
productively or safely during the hottest times of the year.
Over the past few decades, climate change has already prompted global working
capacity to drop, on average, to 90% during the peak summer season, the authors
of the new study said. Worst-case projections envision a continuing plummet to
levels under 40% by the year 2200.
"The gist is that this problem is going to get a lot more severe in the
future," said study lead author John Dunne, an oceanographer with the National
Oceanic and Atmospheric Administration's Geophysical Fluid Dynamics Laboratory,
in Princeton, NJ. "And while the human population has a lot of adaptations for
heat stress, we need to have guidelines and be prepared."
Dunne and his colleagues discuss their observations in a research letter
published in the of the journal Nature Climate Change.
How the study was done
The US National Institutes of Health noted that the combination of extreme
heat and humidity can be hazardous, resulting in heat exhaustion, heat stroke,
dizziness, cramping and rashes.
To conduct its analysis, the study authors first pored over data from the
lab's Earth System Model as well as information collected by the US National
Centers for Environmental Prediction and the National Center for Atmospheric
Research. Collectively the numbers helped to paint a complex picture regarding
climate-change consequences for a period that began in 1861 and stretches out to
At the same time, the authors used widely accepted occupational health and
safety standards to gauge when temperature and humidity conditions become unsafe
for unprotected outdoor work.
In terms of temperature alone, this metric put one goal post at 77 degrees
Fahrenheit, a point at which work activity is not limited by weather. On the
other end, 90 degrees was viewed as a "black flag" condition, in which no
outdoor activity would be considered safe.
By establishing the 1861 to 1960 period as a base reference, the study
authors determined that today's current temperatures reveal that the globe has
already warmed by nearly 2 degrees.
That figure, they said, is expected to double by 2050, prompting unsafe
heat-stress conditions that will cause global working capacity to fall to 80%,
on average. This means that, all things equal, during the hottest months
labourers in such heat-stress zones would have to work 20% less than they could
have before 1960, Dunne said.
Going forward, many possible scenarios could come into play, Dunne said,
depending on shifting greenhouse-gas emission levels, which the team
characterised as an "uncertainty" driven by technology, policy and population
But the team calculated that even a relatively good scenario would see a
nearly 3.6-degree bump by 2200, translating into a labour-capacity slide down to
And the worst-case scenario? A global drop in worker capacity to less than
Heat stress difference
"It's also important to understand that that's just a global average," Dunne
stressed. "In some places the situation will be much worse than others. For
example, in New York the temperature will rise to [84 degrees], whereas in
Bahrain, which is at [nearly 83 degrees] now, it will go up to [96 degrees],
which is above skin temperature."
"That means a person there would be in perpetual heat stress absent air
conditioning," he said. "[In Bahrain], no climatologically safe occupational
labour would be allowable during the hottest months of the year, even at night.
Effectively, worker capacity would be zero."
Another expert weighed in on the issue.
"We're talking about a situation that is very insidious because it's so
subtle," said Solomon Hsiang, who in 2010, as a postdoctoral fellow at Princeton
University's Woodrow Wilson School of Public and International Affairs,
published a paper raising questions about the impact of global heat stress.
"The problem is that one individual may not necessarily notice if the risk of
heat stress makes him or her 1% less productive," said Hsiang, now an assistant
professor with the Goldman School of Public Policy at the University of
California, Berkeley. "But if you make a billion people 1% less productive, that
will have a huge global impact."
To learn more about heat stress, visit the US
National Institutes of Health.