The best way to mitigate this impact on health and labor productivity is to reduce emissions of greenhouse gas pollutants into the Earth’s atmosphere from human activities, the researchers say.

El Niño generally causes warmer temperatures than normal and more heat waves in many areas of the world, and this year’s event is one of the five strongest ever recorded, according to the World Meteorological Organization (WMO).

Although the phenomenon itself is weakening, its impacts will persist, the WMO noted.

With warming of 1.1 degrees since the pre-industrial era, one-fifth of all hours of the year now exceed the permissible threshold for the average outdoor worker doing heavy work in tropical regions, researchers found.

Laboratory studies show a 10% reduction in people’s ability to do physical work under mild heat stress, while the decline is 78% in the case of extreme heat stress.

Added to all this are other health impacts from heat stress, from dehydration to heat stroke, collapse, and long-term influences on the kidneys, brain and heart, which can render people unfit for work.

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