Will large parts of Earth become uninhabitable?

One of the amazing aspects of human history has been our ability to live almost anywhere. In the last 100,000 years or more, humans have migrated to and settled in places as diverse as the Arctic Circle and the Kalahari desert. The last frontier of human settlement was not determined by temperature but by oxygen — few live in altitudes somewhere above 14,000 feet. Recent research suggests that the Sherpas, for example, are descended from people who arrived in that area sometime in the last 5,000 – 10,000 years and adapted slowly to the highest altitudes. They may even have had help from ancestral Neanderthal genes.

Today, we face a different problem. Our current popular view of potential climate disaster often centers around rising seas — think Hurricane Katrina or Superstorm Sandy on a vast scale. Should that come to pass, very large numbers of people would be forced to move inland.

But the damage we are currently doing risks a potentially far more devastating consequence — driving the temperature in large regions past the threshold of where people can work, and ultimately, just survive outdoors. A recent article in the Guardian describes a research study that uses computer models to project that certain areas in a large swath of Asia, from the Persian Gulf to China, will periodically become too hot to survive outdoors for more than a brief period by 2100. The article is a lay explanation of a scientific journal article by a team of researchers from MIT, Loyola Marymount and Hong Kong University of Science and Technology. At least some of it was funded by the Singapore government, which apparently doesn’t agree with the current US government’s dismissal of climate change.

We often think of cold as a killer, but people can survive very cold temperatures surprisingly well with very basic technologies. Witness the Inuit and their relatives who are indigenous to the Arctic Circle around the globe. But our biology cannot tolerate temperatures above about 108F without ceasing to function. Really, we don’t do well above 100F as anyone who has had a fever knows.

We keep our bodies cool by sweating. As the research details, when the temperature and humidity combine to create a wet-bulb temperature  (WBT –that’s sort of like the temperature-humidity index, but not quite) of 35C or 95F we can no longer cool ourselves. Heat builds up rapidly and destructively in our bodies. At this point, we risk death within six hours.

What both articles highlight is that by 2100, large parts of India and Pakistan — notably the areas on the Indus and Ganges rivers — will suffer extreme heat and humidity prior to and during the monsoon season. Parts of Iran, China and Vietnam will also be affected. Wet-bulb temperatures will breach 31C or 88F some of the time, a limit considered dangerous to be outside and essentially impossible to work in.

After that, temperatures could breach the 95 deg wet-bulb limit a few days each year and these regions would simply become impossible in certain months and years. Would people leave and come back? Or would they just abandon the lands and migrate elsewhere? How will people who depend on manual labor to survive and live in rural conditions with no air conditioning live — or will they begin to pack up and leave? Just the very word “inhabitable” may take on new meanings.

The last time such dramatic and lethal climate changes occurred was at the start of the last glacial maximum around 26,000 years ago, when much of the Northern Hemisphere was covered with thick ice. But there were likely less than 1 million people in the entire world then. The regions we are talking about now are home to 1.7 billion people today. Many are farmers, and not farmers sitting in air-conditioned tractors, either. Consider the ramifications of people no longer being able to live and grow food in one of the most densely populated and farmed parts of the world. Places where only a few thousand years ago humanity began the great transition to permanent settlements built around agriculture.

Where will these people go? What will they eat? What will people in other regions who depended on their farming output eat? When we see what the carnage in Syria has wrought in terms of political tension around the world, it’s hard to imagine what societies around the world will do to absorb this. Even if temperatures fall a few degrees short of these projected levels, some people will not be able to tolerate them. People will get sick, people will die. We just don’t really know how bad it will get and how people will react.

If there is a silver lining to this, here it is (from The Guardian):


In Replay Earth, I explore some of the actions the people displaced by climate change might take. I hope that the people of 2100 don’t actually get to find out, but that will depend on what we do in the next decade or two.

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