Katrina, Sandy, now Harvey — we have stared at these storms that have ripped apart the life of communities every few years. Thousands of people’s home lost, in the case of Katrina nearly 2,000 people dead. 100 year storms, 500 year storms, 1,000 year storms — not anymore. We are transitioning to an era when the recent past is not an accurate predictor of the immediate future. But we’re now like the man who got on Interstate 80 in New Jersey to go to California — he knows it will be warmer when he gets there, but no idea what it will be like along the way.

Yet more than computer models and statistical analysis, what’s happening in the places without the economic resources of the United States tells us a lot about what the whole world might look like in the coming decades — be that the 30-60 years of Replay Earth or some time a bit further down the road.

Because while Harvey dominates the news here, The Guardian reports that India, Nepal and Bengladesh are being wracked by their own set of fierce rains, driven by one of the wettest monsoons on record. And the toll is horrific: 1,200 dead, as many as 40 million at risk of loosing their homes to the floods, with at least another day of rain in store.

It’s tempting to think, “Well, that’s India. We have better this or better that,” but that would be foolish. Could Houston survive a storm like this every few years? New Orleans can’t even turn on all its flood relief pumps 12 years after Katrina. And what about when there are 20 Houstons and New Orleans, hit by overlapping storms? Apart from the cold cash involved, do you see a society with the cohesion and will to put aside many competing priorities and spend billions, maybe trillions, on flood control and relief? India is just farther along the curve we’re on.

I don’t know much about India’s weather, but I know I’m seeing a lot of articles about whether Harvey is climate or weather. As a general concept, the distinction between the two is useful and helpful to unconfuse people who think — or want us to think — that global warming means no more cold days. But every day, the climate produces weather — they’re not happening on different planets. The weather we see now is produced by the climate we’ve created in the last 2,000 years, and of course, more so since the advent of universal electricity and the automobile.

That climate is better than the old one at heating up the ocean that is 75% of our planet and the air just above it. That means bigger, wetter storms in some places, just as it means hotter, drier climate in others. Specifically, places like Houston and Mumbai are going to be hammered much more with such storms. Whether there will be more of them, or they will just be longer or more intense, time will tell. But we’re seeing that happen before our very eyes.

This climate will take decades, maybe centuries, to unwind. It will get worse before it gets better, if it gets better. We can speed that up, we can limit some of the damage. But not all of it — we have lost that last moment of control, probably a while ago.

What we can control is how we react and how we learn from that. We are in the early days of a world where most of the time, somewhere, there will be millions — perhaps hundreds of millions or billions — of people homeless or without livelihood from climate change.  We have a lot of work to do.

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):

The analysis also showed that the dangerous 31C WBT level would be passed once every two years for 30% of the population – more than 500 million people – if climate change is unchecked, but for only 2% of the population if the Paris goals are met. “The problem is very alarming but the intensity of the heatwaves can be reduced considerably if global society takes action,” said [study author] Eltahir.

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.