How Hot Would The Earth Have To Get Before It Would Be Unlivable?

Illustration for article titled How Hot Would The Earth Have To Get Before It Would Be Unlivable?

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.


Huber added:

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.

via Purdue University


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So, someone moves into an underground home hoping for some lower temps. Then you have to deal with food and air circulation.

Food - since we'd all be moving off the surface of the earth to underground structures, plants will reclaim the world, and a little late-night foraging will supply some much-needed vitamins and minerals. Animals... we'll probably be living off lizard meat, since they handle the heat better than us.

Someone mentioned mushrooms. Actually, given a high-humidity environment, those might be a problem. Fungus grows wicked fast in high-humidity environments. People are going to have all sorts of hygiene issues, and trying to find ways to maintain soap production in an underground dwelling will be interesting. Lye soap might experience a comeback, since it's basically made from wood ash & water mixed with fat.

Electricity will go down the tubes; most electricity-generating solutions are going to have a very, *very* high breakdown rate in a high humidity dense plant-growth environment. And once certain components break down, they're going to be very difficult to replace. So we're back to torches.

Airflow in your underground dwelling is going to be difficult to manage - you need enough air to provide oxygen, but not so much it begins to heat the walls and rock.

And all of this is possibly only a temporary solution anyways, since once the surface temp rises, the earth's crust is going to begin to rise in temperature too. I don't know how long it will take, but right now "underground" is only cool because of the high thermal load it would require to heat it, the fact that most of the time the planet is fairly cool - nights, winters, etc. If those heat-dispersion times begin to go away, underground temps will begin to rise as well.