A new study indicates that one billion people could be forced to either live with “insufferable heat”, or to move to avoid it within 50 years. That’s with an increase in global temperature of just one additional degree Celsius. Because it’s a global problem, we often talk about global trends in temperature, weather, and so on. That makes a lot of sense, but it also makes it hard to gauge exactly what we should expect as the planet continues to warm.

Most people regularly experience shifts in temperature that can cover 10°C or more in a single day, so it’s easy to feel that a global change in temperature of less than 2°C is no biggie. If we use “common sense”, there are far bigger problems to deal with than adding a couple degrees to the top end of a daily temperature swing, right?

Unfortunately, while averages are useful in many ways, they can also mislead when talking about an area the size of Earth’s surface. One example I really like is sea level. As with average global temperature, there’s a lot of discussion of average sea level rise as the planet warms, and that has led to a fair amount of confusion. Most people’s interaction with water levels happens at a small enough scale that gravity’s effects aren’t perceptible. You raise the level of water in a bathtub, and you can measure that change pretty evenly, accounting for a bit of sloshing. That doesn’t really apply to a “container” like the Earth, however, because despite a bit of weird controversy, the earth is not flat, and water isn’t “held in” by the sides of the oceans the way it is by the sides of a tub. This video from Minute Physics gives a good intro to the factors that go into the rather irregular “level” of the oceans around the planet:

Sea level is further complicated by things like the melting ice cap on Greenland, with is causing a dramatic loss of mass on top of that island. That means that the Earth’s crust is rising up as the weight on top if it is reduced. It also means that the gravitational pull from the ice mass is declining relative to other centers of gravity acting on the water, so the ocean is receding away from it in response. Both of these mean that sea level rise will be higher in other places, like the UK, not just because of melting land ice and thermal expansion, but also because the shape of the sea floor, and the gravitational pull on the water are also changing.

Simply calculating the global average sea level rise won’t give you an accurate picture of what that will look like in any one location.

The same can be said of average temperature. The tilt of Earth’s axis relative to the sun means that as we orbit our star, we get seasonal shifts in temperature. Those changes get more dramatic as you get closer to the poles, as the North or South of the planet get more or less direct sunlight, depending on the angle at which it reaches us.

Except that it’s not really that simple. I grew up in New England, for example. For those who don’t know, that’s a cluster of small states in the Northeastern corner of the U.S. – Maine, New Hampshire, Vermont, Massachusetts, Connecticut, and Rhode Island. I lived in Massachusetts and New Hampshire, mostly, and regularly visited relatives in Maine. As such, I experienced weather that got above 100°F (37.8°C) in the summer, and as low or lower than -10°F (-23.3°C) in the winter. That range in temperature also came with dramatic thunderstorms, the occasional tornado (which I was lucky enough to not experience directly), and also blizzards, ice storms, and frozen pipes.

If you were to only look at the average annual high and low temperatures for Boston, Massachusetts, you’d be expecting a range, over the course of the year, between a low of 44°F (6.7°C), and a high of 59°F(15°C), and you would be woefully unprepared for the heat of the summer, or the cold of the winter. You would not be expecting much in the way of snow or ice.

My current location, Glasgow, is much, much farther north. I’m at about the same latitude as Moscow, Russia, and north of most major cities in Canada. Despite that, it’s uncommon to see a full day below 32°F(0°C) here, even with winters that are much longer/darker than I’m used to, and I doubt I’ll see many days that pass 80°F(26.7°C) this summer. It’s a much milder climate all around, despite being so far north, because of the heat being constantly delivered to Western Europe by the Gulf Stream. The one place I’ve ever been to that has been historically cold enough year-round to have glaciers was the peak of Mt. Kilimanjaro, made that cold by elevation despite being just barely south of the Equator.

There are a lot of factors that influence the temperature all over the planet, and those extremes mean that as the average temperature of the planet continues to increase, not only will the extremes change, but the physics driving those differences are also likely to change. Wind and water move a great deal of heat around the planet, powered by those very temperature differences, as well as the way the planet spins. That constant motion means that the global increase in temperature will continue to be uneven. The average will rise, as it has been doing, but some places will barely notice a temperature change, while others will see such massive increases that life may become difficult, or even impossible: 

The human cost of the climate crisis will hit harder, wider and sooner than previously believed, according to a study that shows a billion people will either be displaced or forced to endure insufferable heat for every additional 1C rise in the global temperature.

In a worst-case scenario of accelerating emissions, areas currently home to a third of the world’s population will be as hot as the hottest parts of the Sahara within 50 years, the paper warns. Even in the most optimistic outlook, 1.2 billion people will fall outside the comfortable “climate niche” in which humans have thrived for at least 6,000 years.

The authors of the study said they were “floored” and “blown away” by the findings because they had not expected our species to be so vulnerable.

“The numbers are flabbergasting. I literally did a double take when I first saw them, ” Tim Lenton, of Exeter University, said. “I’ve previously studied climate tipping points, which are usually considered apocalyptic. But this hit home harder. This puts the threat in very human terms.”

Instead of looking at climate change as a problem of physics or economics, the paper, published in the Proceedings of the National Academy of Sciences, examines how it affects the human habitat.

The vast majority of humanity has always lived in regions where the average annual temperatures are around 6C (43F) to 28C (82F), which is ideal for human health and food production. But this sweet spot is shifting and shrinking as a result of manmade global heating, which drops more people into what the authors describe as “near unliveable” extremes.

Humanity is particularly sensitive because we are concentrated on land – which is warming faster than the oceans – and because most future population growth will be in already hot regions of Africa and Asia. As a result of these demographic factors, the average human will experience a temperature increase of 7.5C when global temperatures reach 3C, which is forecast towards the end of this century.

At that level, about 30% of the world’s population would live in extreme heat – defined as an average temperature of 29C (84F). These conditions are extremely rare outside the most scorched parts of the Sahara, but with global heating of 3C they are projected to envelop 1.2 billion people in India, 485 million in Nigeria and more than 100 million in each of Pakistan, Indonesia and Sudan.

This kind of looming danger is why I believe that our efforts to deal with climate change have to go beyond merely crunching the numbers on energy demand, emissions, and so on. That’s important work to do, but it must come along with massive changes in how we distribute resources, design cities, and decide who lives where and under what conditions. If we don’t move away from valuing property and profit over the requirements for human life and wellbeing, then the human death and suffering of this century will be beyond anything in human history.

It’s been pointed out many times that we technically grow more food than is needed to feed everyone on this planet. Despite that, there are people all over the world who either starve to death, or are chronically malnourished. The biggest reason for this is that distributing the food based on need is not profitable for the rich and powerful, and the global economy treats the wealth and power of the “elites” as more important than bare survival.

Over the last few decades, every crisis has come with a chorus of rich people pushing for general austerity and talking about how everyone must “tighten their belts”. At the same time, the planet’s richest have grown ever more wealthy, and action on climate change is constantly opposed because of the cost.

Millions will die from global warming this century because of that greed. It may be that that can be avoided, but it seems increasingly unlikely. Without moving away from the current global capitalist model, those deaths will be numbered in the billions. Extreme heat comes with a whole host of problems ranging from the colossal wildfires we’ve seen in Australia, to more volatile, deadly air pollution, to drought, flooding, and associated crop failures. Dealing with any of this will require that resources be distributed based not on misguided, capitalist notions of ownership and property, but on what is actually required to allow people to live, and to mitigate the damage done to the ecosystems on which we depend.

Harder times are coming, and we cannot afford to indulge an entire class of spoiled, greedy sociopaths who think they deserve to decide who lives and who dies.

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