Because of humanity's contribution to climate change, the authors wrote, some population centers in West Asia "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 hu man body to reduce its temperature through sweating and ventilation. That threatens anyone without air-conditioning, including the poor, but also those who work outdoors in professions like agriculture and construction.

The paper, published in Nature Climate Change, was written by Jeremy S Pal of the department of civil engineering and environmental science at Loyola Marymount University and Elfatih A B Eltahir of Massachusetts Institute of Technology. Previous studies suggested that such conditions might be reached within 200 years. But the new research, which depends on climate models that focus on regional to pography and conditions, foresees a shorter timeline.

The researchers resolve the old argument over whether the source of summer misery is the heat or the humidity by saying that it is both. They rely on a method of measuring atmospheric conditions known as wet-bulb temperature, which, while less well known and understood than the standard method of measuring temperatures, describes the extent to which evaporation and ventilation can reduce an object's temperature.

Since even today's heat waves cause premature deaths by the thousands, mainly affecting very young, elderly and infirm people, the more extreme conditions envisioned "would probably be intolerable even for the fittest of humans, resulting in hyperthermia" after six hours of exposure. As climate change causes temperatures to rise, it should come as no surprise that the warm-water coasts in West Asia could be the first to experience brutal combinations of heat and humidity.

The conditions would not be constant, but spikes would become increasingly common.