If global temperatures rise just 21 degrees Fahrenheit, half of humanity will be cooked. A recent study shows that the planet doesn't have to warm up very much before it becomes unlivable. And the death blow comes from humidity.
Atmospheric scientist Matthew Huber used computer simulations to determine what would happen in a worst-case climate change scenario. He asked what would happen if carbon emissions raised average planetary temperatures 21 degrees higher than the 2007 average. Then he calculated what that would mean for every region of the globe. In the map above, you can see the result - white and purplish land areas exceed the limit where scientists believe humans would experience a potentially lethal level of heat stress.
The key to Huber's work is the idea of "wet bulb temperature," which is what he used to make his calculations about livability. According to a release about his research, which will be published this week in Proceedings of the National Academy of Sciences:
Wet-bulb temperature is equivalent to what is felt when wet skin is exposed to moving air. It includes temperature and atmospheric humidity and is measured by covering a standard thermometer bulb with a wetted cloth and fully ventilating it. The researchers calculated that humans and most mammals, which have internal body temperatures near 98.6 degrees Fahrenheit, will experience a potentially lethal level of heat stress at wet-bulb temperature above 95 degrees sustained for six hours or more.
Although areas of the world regularly see temperatures above 100 degrees, really high wet-bulb temperatures are rare. This is because the hottest areas normally have low humidity, like the 'dry heat' referred to in Arizona. When it is dry, we are able to cool our bodies through perspiration and can remain fairly comfortable. The highest wet-bulb temperatures ever recorded were in places like Saudi Arabia near the coast where winds occasionally bring extremely hot, humid ocean air over hot land leading to unbearably stifling conditions, which fortunately are short-lived today . . . We found that a warming of 12 degrees Fahrenheit would cause some areas of the world to surpass the wet-bulb temperature limit, and a 21-degree warming would put half of the world's population in an uninhabitable environment.
You can take this study as a warning about global warming caused by carbon emissions, or you can simply take it as an interesting futurist prediction. The Earth underwent many phases of natural heating and cooling, long before Homo sapiens was in the picture. If we enter another heating phase, regardless of the cause, it won't take much before half the planet will be off-limits to anyone who can't afford an air conditioned atmosphere dome.