A study published on May 4th by the Proceedings of the National Academy of Sciences finds that over the next 50 years, up to 3.5 billion people will find their existing home intolerably hot, sending them in search of cooler climes. The consequences for the human community could be severe, especially at a time when fear and loathing of immigrants is the dominant cultural norm in many countries.
Here is the abstract from that study.
All species have an environmental niche, and despite technological advances, humans are unlikely to be an exception. Here, we demonstrate that for millennia, human populations have resided in the same narrow part of the climatic envelope available on the globe, characterized by a major mode around ∼11 °C to 15 °C mean annual temperature (MAT). Supporting the fundamental nature of this temperature niche, current production of crops and livestock is largely limited to the same conditions, and the same optimum has been found for agricultural and nonagricultural economic output of countries through analyses of year-to-year variation.
We show that in a business-as-usual climate change scenario, the geographical position of this temperature niche is projected to shift more over the coming 50 y than it has moved since 6000 BP. Populations will not simply track the shifting climate, as adaptation in situ may address some of the challenges, and many other factors affect decisions to migrate.
Nevertheless, in the absence of migration, one third of the global population is projected to experience a MAT >29 °C currently found in only 0.8% of the Earth’s land surface, mostly concentrated in the Sahara. As the potentially most affected regions are among the poorest in the world, where adaptive capacity is low, enhancing human development in those areas should be a priority alongside climate mitigation.
The caption for the above graphic from the study reads as follows: “Expansion of extremely hot regions in a business-as-usual climate scenario. In the current climate, MATs >29 °C are restricted to the small dark areas in the Sahara region. In 2070, such conditions are projected to occur throughout the shaded area following the RCP8.5 scenario. Absent migration, that area would be home to 3.5 billion people in 2070 following the SSP3 scenario of demographic development. Background colors represent the current MATs.”
Finding Our Comfort Zone
The research, led by Dutch research ecologist Marten Scheffer of the Santa Fe Institute and Wageningen University, studied where people have lived over the past 6000 years and the average mean temperatures in those areas. It finds the “sweet spot” for most of the world’s population is a mean average temperature of 51 to 59 degrees Fahrenheit. Some areas such as India have adapted to temperatures between 68 and 75 degrees F.
The problem is that by 2070, about 19% of the surface of the Earth will have a MAT of more than 84 degrees F. Today, less then 1% of the Earth experiences mean average temperatures that high. The researchers estimate there will be 3.5 billion people living in those elevated temperature zones 50 years from now.
Co-author Tim Kohler, an archaeologist at Washington State University, tells the Washington Post that while our technological progress has allowed us to settle virtually everywhere on Earth, and even in space, the study shows, “Our preferences (as opposed to our abilities) have long been for a rather narrow band of temperatures in which we typically have our densest numbers and greatest economic success. It’s a bit unfortunate that most population growth happens to be in the place that will be hardest to live in.”
“Populations have avoided stifling hot or freezing temperatures in large numbers, concentrating instead on the goldilocks zones,” Neil Adger, professor of human geography at the University of Exeter, tells the Post. He reviewed an early copy of the study but was not involved in the research itself.
The study assumes a “business as usual” approach to climate change that lowers carbon emissions, but not by nearly enough to keep average global temperatures from rising significantly over the next 50 years. Even if humans do find a way to reduce carbon emissions significantly, temperatures will continue to increase for decades, much the way a supertanker continues merrily on its way long after its propellers stop turning.
“It is likely climatic changes will in effect move large cities and whole countries into temperature niches that present inhabitants would find unimaginable,” Adger says. “So will cities move? Unlikely. But will they become less attractive destinations for people to move to? Definitely. And ultimately some present cities will stop growing and ossify.”
“A key unknown is whether labor productivity for outdoor work can adapt to these new niches. Even if plant breeding technologies can solve the temperature tolerance of crops, can technologies help farming practices, which are always labor intensive, to be tolerable? Ultimately, we will witness imperceptible shifts that over decades will represent a profound shift in the economic geography of the human world.”
Dramatic Changes Coming
John Schellnhuber is the director emeritus of the Potsdam Institute for Climate Impact Research and has acted as an advisor to German chancellor Angela Merkel on climate change. He tells the Washington Post the study is useful because it confirms “the rather small historic habitat of humankind on Earth.” It also shows the coming, dramatic shifts global warming will have on that habitat and also shows that “large-scale migration needs to be part of a global adaptation strategy.”
If you want a preview of how mass migrations will affect the political stability of the world, you need only look at the exodus that has already begun from Central America and Syria. Those people have been vilified, hidden away in wretched refuge camps, or incarcerated. Imagine what will happen as the trickle of migrants becomes a flood and then a tidal wave.
Scientists already know that lobsters are migrating north in search of cooler waters. The mangrove forests along the eastern seaboard of the United States have begun migrating north of their traditional home in Florida to Georgia and South Carolina. Like frogs in a pot of warming water, humans will soon begin leaving their ancestral homes in search of cooler temperatures.
There is evidence that Antarctica was once a lush rainforest. Perhaps in a few decades or centuries it could be one again, with yacht races in the Ross Sea and condominiums on the shores of Queen Mary Land. As Steely Dan would say, “What a beautiful world this will be. What a glorious time to be free.”