"In many major crop regions, workers plant and harvest in spiraling heat and humidity,"

...

"If this affects humans' ability to grow food, that's serious," said lead author Connor Diaz, who did the research as a Columbia University undergraduate student with scientists at the university's Lamont-Doherty Earth Observatory. "The global food chain is all connected, and the danger is, this will impact crop production."

Higher temperatures alone are oppressive, but high relative humidity greatly increases the effects... High humidity is especially prevalent in major tropical and subtropical crop regions in river deltas and near coasts, which supply plenty of moisture for the air to soak up...

Combined heat and humidity are gauged on the "wet bulb" scale, which factors in air temperature, water-vapor content and wind conditions. The authors of the new study define 27 degrees Centigrade wet-bulb as the point where farmworkers will begin struggling...

The new study found that many major agricultural regions already experience three months of 27C conditions or worse during the year as a whole. These include the Amazon, northern Colombia and parts of Mexico; the coasts of the Red Sea and Persian Gulf; southeast Asia; and much of Malaysia and Indonesia. Countries that see two months or more include Senegal, Ivory Coast, Nigeria, Cameroon and the northern region of Australia...

The most common means of adapting to rising temperatures in the U.S. and most other countries has been to shift work hours into the night. Allowing workers to reduce their pace and effort, and increasing break times can also help, and some U.S. states and countries such as Spain have mandated such measures. But these efforts reduce worker productivity, which may feed into higher food prices. And fancier adaptations, like air-conditioned retreat spaces and air-conditioned tractors are simply not feasible in much of the world...