WASHINGTON • By the end of this century, areas of the Persian Gulf could be hit by waves of heat and humidity so severe that simply being outside for several hours could threaten human life, according to a study published on Monday.
Because of humanity's contribution to climate change, the authors wrote, some population centres in the Middle East "are likely to experience temperature levels that are intolerable to humans".
The dangerously muggy summer conditions predicted for places near the warm waters of the gulf could overwhelm the ability of the human body to reduce its temperature by sweating and ventilation. That threatens anyone without air-conditioning, including the poor, but also those who work outdoors, such as in agriculture and construction.
The paper, published in the journal Nature Climate Change, was written by Dr Jeremy Pal of Loyola Marymount University in Los Angeles and Dr Elfatih Eltahir of the Massachusetts Institute of Technology.
Previous studies had suggested that such conditions might be reached within 200 years. But the new research, which depends on detailed climate models that focus on regional topography and conditions, foresees a shorter timeline.
The researchers resolved the old argument over whether the source of summer misery is the heat or the humidity by saying it is both. They relied on a method of measuring atmospheric conditions known as wet bulb temperature, which describes the extent to which evaporation and ventilation can lower an object's temperature. A wet bulb thermometer has, literally, a wet bulb: It is wrapped in a moistened cloth. If the wet bulb temperature is 35 deg C, that means that even a person drenched in sweat cannot cool off.
Wet bulb readings are not the same as the heat index measurements used by the National Weather Service, Dr Eltahir said. (This is the figure used by weather forecasters to say what a hot day "feels like" when the humidity is added.) A wet bulb measure of 35 deg C, he estimated, would roughly translate to a heat-index reading of 73.9 deg C.
Since even today's heatwaves cause premature deaths by the thousands, mainly affecting very young, elderly and infirm people, the more extreme conditions envisioned in the paper "would probably be intolerable even for the fittest of humans, resulting in hyperthermia" after six hours of exposure, the study says.
As climate change causes temperatures to rise globally, it should come as no surprise that the warm-water coasts in the Middle East could be the first to experience brutal combinations of heat and humidity. The conditions would not be constant, but spikes would become increasingly common.
A temperature that today would rank in the 95th percentile "becomes approximately a normal summer day" by the end of the century, the researchers said. Wet bulb temperatures that even exceed the 35 deg C threshold could be expected to occur once every 10 or 20 years, Dr Eltahir said. "When they happen, they will be quite lethal."
The research raises the prospect of "severe consequences" for the haj, the annual pilgrimage that draws roughly two million people to Mecca to pray outdoors from dawn to dusk. Should the haj, which can occur at various times of the year, fall during the height of the summer, "this necessary outdoor Muslim ritual is likely to become hazardous to human health", the authors predicted.
If nations reduce their greenhouse gas emissions, the authors concluded, the predicted disasters can be prevented. "Such efforts applied at the global scale would significantly reduce the severity of the projected impacts."
NEW YORK TIMES