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Study: Global warming could make survival in tropics impossible

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Humans may not be able to survive heat conditions in tropical locales like South Florida if global warming is not curbed, according to Phys.org

Adherence to the Paris Agreement could keep tropical regions from reaching temperatures that are beyond human tolerability, the new study projects.

Researchers estimate that “if countries are able to cap warming at 1.5 degrees Celsius above pre-industrial levels, the tropics will be spared temperatures that surpass the ‘survival limit.’ But life in the world’s hottest latitudes could become intolerable if those controls aren’t met.”

The study focused on a measure called “wet-bulb temperature,” which accounts for heat and humidity, and is similar to the meteorological term “heat index.”

“The general idea is, the body doesn’t just respond to temperature, it responds to humidity,” said Kristina Dahl, a climate scientist who was not involved in the study.

The body cools itself primarily through sweating and the evaporation of sweat from the skin, Dahl explained. At a certain heat-humidity point, she said, it becomes “thermodynamically difficult” for that to happen.

Scientists believe that a wet-bulb temperature of 35 degrees C is the upper limit of human tolerance. It’s akin to a heat index of 160 degrees Fahrenheit.

People vary in how much heat they can stand. But at a wet-bulb temperature of 35 degrees C, anyone lingering outdoors would be in trouble.

The body normally maintains a fairly stable internal temperature of 37 degrees C (98.6 degrees F). Skin temperature has to be a little lower, to allow core heat to flow to the skin. If it’s not, a person’s internal temperature could quickly rise, explained Yi Zhang, the lead researcher on the new study.

“High core temperatures are dangerous or even lethal,” said Zhang, a graduate student in atmospheric and oceanic sciences at Princeton University in New Jersey.

Averting intolerable wet-bulb temperatures does not, however, mean the planet is out of the woods. Human health can certainly suffer under less-extreme heat, she noted.

Heat waves routinely cause sometimes fatal heat illness and feed insect-borne infections like Lyme disease and Zika, for example, or contaminate food and water supplies by causing rising sea levels, heavy rains and flooding. Tropical areas most at risk are the Amazon rain forest, a large share of Africa, the Indian peninsula and parts of Southeast Asia.

Warming also contributes to air pollution, which can exacerbate chronic health conditions like heart and lung disease, Dahl added.

Human-generated emissions—chiefly carbon dioxide, as well as nitrous oxide and methane are blamed for the rise in global temperatures since the 1950s. In the United States, most of those emissions come from burning fossil fuels for energy use, according to the U.S. Energy Information Administration.