Climate Crisis Is on Track to Push One-Third of Humanity Out of Its Most Livable Environment - ProPublica

Climate change is remapping where humans can exist on the planet. As optimum conditions shift away from the equator and toward the poles, more than 600 million people have already been stranded outside of a crucial environmental niche that scientists say best supports life. By late this century, according to a study published last month in the journal Nature Sustainability, 3 to 6 billion people, or between a third and a half of humanity, could be trapped outside of that zone, facing extreme heat, food scarcity and higher death rates, unless emissions are sharply curtailed or mass migration is accommodated.

The research, which adds novel detail about who will be most affected and where, suggests that climate-driven migration could easily eclipse even the largest estimates as enormous segments of the earth’s population seek safe havens. It also makes a moral case for immediate and aggressive policies to prevent such a change from occurring, in part by showing how unequal the distribution of pain will be and how great the improvements could be with even small achievements in slowing the pace of warming.

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The new study reconsiders population growth and policy options and explores scenarios that dramatically increase earlier estimates, demonstrating that the world’s environment has already changed significantly. It focuses more heavily on temperature than precipitation, finding that most people have thrived in mean annual temperatures of 55 degrees Fahrenheit.

Should the world continue on its present pathway — making gestures toward moderate reductions in emissions but not meaningfully reducing global carbon levels (a scenario close to what the United Nations refers to as SSP2-4.5) — the planet will likely surpass the Paris Agreement’s goal of limiting average warming to 1.5 degrees Celsius and instead warm approximately 2.7 degrees. That pathway, which accounts for population growth in hot places, could lead to 2 billion people falling outside of the climate niche within just the next eight years, and 3.7 billion doing so by 2090. But the study’s authors, who have argued in other papers that the most extreme warming scenarios are well within the realm of possibility, warn that the worst cases should also be considered. With 3.6 degrees of warming and a pessimistic climate scenario that includes ongoing fossil fuel use, resistance to international migration and much more rapid population growth (a scenario referred to by the U.N. as SSP3-7), the shifting climate niche could pose what the authors call “an existential risk,” directly affecting half the projected total population, or, in this case, as many as 6.5 billion people.

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Slowing global emissions would dramatically reduce the number of people displaced or grappling with conditions outside the niche. If warming were limited to the 1.5 degrees Celsius targeted by the Paris accords, according to a calculation that isolates the effect of warming, half as many people would be left outside of the optimal zone. The population suffering from extreme heat would be reduced fivefold, from 22% to just 5% of the people on the planet.

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According to the study, India will have, by far, the greatest population outside of the climate niche. At current rates of warming, the researchers estimate that more than 600 million Indians will be affected, six times more than if the Paris targets were achieved. In Nigeria, more than 300 million citizens will be exposed, seven times more than if emissions were steeply cut. Indonesia could see 100 million people fall out of a secure and predictable environment, the Philippines and Pakistan 80 million people each, and so on. Brazil, Australia and India would see the greatest area of land become less habitable. But in many smaller countries, all or nearly all the land would become nearly unlivable by traditional measures: Burkina Faso, Mali, Qatar, the United Arab Emirates, Niger. Although facing far more modest impacts, even the United States will see its South and Southwest fall toward the hottest end of the niche, leading to higher mortality and driving internal migration northward.

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