Global Warming’s Deadly Combination: Heat and Humidity
A new study suggests that large swaths of the tropics will experience dangerous living and working conditions if global warming isn’t limited to 1.5 degrees Celsius.
Here’s one more reason the world should aim to limit warming to 1.5 degrees Celsius, a goal of the international Paris Agreement: It will help keep the tropics from becoming a deadly hothouse.
“An important problem of climate research is what a global warming target means for local extreme weather events,” said Yi Zhang, a graduate student in geosciences at Princeton University and the study’s lead author. “This work addresses such a problem for extreme TW.”
The study is in line with other recent research showing that high heat and humidity are potentially one of the deadliest consequences of global warming.
“We know that climate change is making extreme heat and humidity more common,” said Robert Kopp, a climate scientist at Rutgers University who was not involved in the study. “And both of those things reduce our ability to live in a given climate.”
Ms. Zhang, along with two other Princeton researchers, Isaac Held and Stephan Fueglistaler, looked at how the combination of high heat and high humidity is controlled by dynamic processes in the atmosphere. They found that if global warming is limited to 1.5 degrees, the wet-bulb temperature at the surface can approach but not exceed 35 degrees Celsius, or 95 degrees Fahrenheit, in the tropics.
Above a wet-bulb temperature of 35 Celsius, the body cannot cool down, as sweat on the skin can no longer evaporate. Prolonged exposure to such conditions can be fatal, even for healthy people. Lower but still high wet-bulb temperatures can affect health and productivity in other ways.
Ms. Zhang cautioned that the effect on health from her study was uncertain, since she and her colleagues looked only at how high wet-bulb temperatures would get, not how often the extremes would be reached or how long they would last. “Thorough knowledge on the health impact of intensity, frequency, and duration of high wet-bulb temperatures is needed,” she said.
The study was published in the journal Nature Geosciences.
A growing body of research has found that global warming so far is taking an increasing toll on human health indirectly through drought and crop failures, extreme storms and flooding, increased spread of certain insect-borne diseases and other effects.
But heat also has direct effects on the human body. Even relatively dry heat can be enough to kill people, as evidenced by the toll from heat waves in recent years. And the combination of heat and high humidity has already reached dangerous levels in parts of the world.
The effects of heat and humidity are worse for women, older people and those with chronic conditions like diabetes and hypertension, said Glen Kenny, a professor of physiology at the University of Ottawa who studies how the body copes with heat stress.
Work or exercise generates heat, and the body has to dissipate it. If the air temperature is higher than body temperature, the main source of cooling is through evaporation of sweat. But if the humidity reaches a point where sweat cannot evaporate, “essentially the body will gain heat,” said Dr. Kenny, who was not involved in the new study.
That stresses the cardiovascular system. “The strain that the heart is facing becomes progressively greater, especially if there’s successive days of heat exposure,” he said.
Source: New York Times