Global Heating could make it too Hot for a Third of Humanity by 2080

Juan Cole 05/25/2023

Ann Arbor (Informed Comment) – A lot of studies have focused on the economic cost of global heating, caused by humans burning fossil fuels. A new study in Nature Sustainability "Quantifying the human cost of global warming," by Timothy M. Lenton et al. instead concentrates on what heating will mean for the lives of human beings.

The authors identify a "human climate niche," of parts of the earth with temperate climates suitable to human well-being, which they argue have been relatively stable for thousands of years. That's where we tend to live. As the globe heats up, however, the human climate niche is shrinking, and large populations are being kicked out of it into, well, hell.

The authors write, "We show that climate change has already put ~9% of people (>600 million) outside this niche." Those 600 million people live in places like North Africa, the Middle East, Pakistan and India. This change just happened, 1960-1990, so hundreds of millions are already being disadvantaged by global heating.

But remember that our future is in our hands. We can abolish fossil fuels in a generation and keep extra warming to 1.5 degrees C. (2.7 degrees F.) above pre-industrial levels. We can do it, and it is perfectly plausible that we will do it. Remember that the oceans will absorb all the extra CO2 if we don't outrun their absorptive capacity. That wouldn't happen until after 2050. The Nature Sustainability article is about what happens if we just don't do it.

NASA has a map showing where average temperatures are on the hot side:

Now what happens in the next 60 to 80 years if humanity heats up the earth by 4.86° F. (2.7 °C) , Lenton and his colleagues ask. That is after all pretty much where we are headed at today's rates of human carbon emissions. There will likely be about 10 billion human beings by then, up from about 8 billion this year.

They answer:

"By end-of-century (2080–2100), current policies leading to around 2.7 °C global warming could leave one-third (22–39%) of people outside the niche."

The lower end of their assessment would equal 2.2 billion people, but the higher end would be 3.9 billion people. That would be 80% of everybody now living in Asia. It is huge, ginormous. A lot of the newspapers reporting on these findings went with the "2 billion" estimate, but the authors are estimating 3.3 billion ("one-third") as the likeliest number affected.

They also provide some concrete details about what this kind of heat would mean for people. They point out that high temperatures can detract from labor productivity. Imagine being up on a building as a carpenter when it is 113° F. I worked on buildings when I was a teenager, and one reason we began the work day early, around 6:30 am, was that the weather was pleasant in the summer at that time of day. I was living in Qatar in the Gulf in 2018, and by the end of May I didn't so much as want to take a 15 minute walk in the heat — it really did get up to 113° F. People told me they got depressed in the summer from having to be inside all the time with air conditioning.

Farming in the heat is also no fun, since in a lot of the world people still do a lot of manual labor on the farm. The authors point out that not only do humans have a comfy climate niche, but so do the crops they raise, and if the crops can't take the increased level of heat, the humans who cultivate them will be out of luck.

In a really hot climate, too, the authors say, learning and cognitive performance suffer. So much for trying to school children or conduct college teaching and research.

High temperatures contribute to miscarriages. So pro-life Republicans should be really concerned to fight climate change, right?

And extremes of heat cause higher rates of death in general.

The Economist observes, "Between 2010 and 2019, the incidence of heatwaves in India grew by a quarter compared with the previous decade, with a corresponding increase in heat-related mortality of 27%."

Even just 104° F. (40 °C) and above can be deadly to human beings. The lethality of those temperatures goes way up if it is really humid, as well. Humans cool off by sweating, but that mechanism stops working at those extremes. Scientists have discovered that a combination of 120° F. and 80 percent humidity will kill you dead.

High temperatures can contribute to conflict and warfare, since they are usually associated with extra aridity and drought. They can also cause mass migration to cooler places. The future may belong to Canada and Chile rather than to Arizona and Gujarat. But as we already see with the migrant crisis in Europe, millions of people on the move can also cause political and social upheavals.

Lenton and his colleagues conclude by warning, "The worst-case scenarios of ~3.6 °C (6.4° F.) or even ~4.4 °C (7.9° F.) global warming could put half of the world population outside the historical climate niche, posing an existential risk."

So they are saying that if we go really wild with the carbon emissions and raise the average surface temperature of the earth by 6 to 8 degrees F. over the pre-industrial average, we would create unbearable hot spots where 50% of all humans live.

The authors are wondering whether a change of that magnitude would even be survivable by the human race. I take it that is what they mean by existential risk.

A cheery note to end on.

Filed Under: Climate Crisis, Drought, Extreme Heat, Featured, wildfires