Persian Gulf could experience deadly heat

The research reveals details of a business-as-usual scenario for greenhouse gas emissions, but also shows that curbing emissions could forestall these deadly temperature extremes.

The study, published in the journal Nature Climate Change, was carried out by Elfatih Eltahir, a professor of civil and environmental engineering at MIT, and Jeremy Pal PhD '01 at Loyola Marymount University. They conclude that conditions in the Persian Gulf region, including its shallow water and intense sun, make it "a specific regional hotspot where climate change, in absence of significant mitigation, is likely to severely impact human habitability in the future."

Running high-resolution versions of standard climate models, Eltahir and Pal found that many major cities in the region could exceed a tipping point for human survival, even in shaded and well-ventilated spaces. Eltahir says this threshold "has, as far as we know ... never been reported for any location on Earth."

That tipping point involves a measurement called the "wet-bulb temperature" that combines temperature and humidity, reflecting conditions the human body could maintain without artificial cooling. That threshold for survival for more than six unprotected hours is 35 degrees Celsius, or about 95 degrees Fahrenheit, according to recently published research. (The equivalent number in the National Weather Service's more commonly used "heat index" would be about 165 F.)

This limit was almost reached this summer, at the end of an extreme, weeklong heat wave in the region: On July 31, the wet-bulb temperature in Bandahr Mashrahr, Iran, hit 34.6 C -- just a fraction below the threshold, for an hour or less.

But the severe danger to human health and life occurs when such temperatures are sustained for several hours, Eltahir says -- which the models show would occur several times in a 30-year period toward the end of the century under the business-as-usual scenario used as a benchmark by the Intergovernmental Panel on Climate Change.

The Persian Gulf region is especially vulnerable, the researchers say, because of a combination of low elevations, clear sky, water body that increases heat absorption, and the shallowness of the Persian Gulf itself, which produces high water temperatures that lead to strong evaporation and very high humidity.

The models show that by the latter part of this century, major cities such as Doha, Qatar, Abu Dhabi, and Dubai in the United Arab Emirates, and Bandar Abbas, Iran, could exceed the 35 C threshold several times over a 30-year period. What's more, Eltahir says, hot summer conditions that now occur once every 20 days or so "will characterize the usual summer day in the future."

While the other side of the Arabian Peninsula, adjacent to the Red Sea, would see less extreme heat, the projections show that dangerous extremes are also likely there, reaching wet-bulb temperatures of 32 to 34 C. This could be a particular concern, the authors note, because the annual Hajj, or annual Islamic pilgrimage to Mecca -- when as many as 2 million pilgrims take part in rituals that include standing outdoors for a full day of prayer -- sometimes occurs during these hot months.

While many in the Persian Gulf's wealthier states might be able to adapt to new climate extremes, poorer areas, such as Yemen, might be less able to cope with such extremes, the authors say.