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.
“There are clear, profound ethical consequences in the numbers,” Timothy Lenton, one of the study’s lead authors and the director of the Global Systems Institute at the University of Exeter in the U.K., said in an interview. “If we can’t level with that injustice and be honest about it, then we’ll never progress the international action on this issue.”
The notion of a climate niche is based on work the researchers first published in the Proceedings of the National Academy of Sciences in 2020, which established that for the past 6,000 years humans have gravitated toward a narrow range of temperatures and precipitation levels that supported agriculture and, later, economic growth. That study warned that warming would make those conditions elusive for growing segments of humankind and found that while just 1% of the earth’s surface is now intolerably hot, nearly 20% could be by 2070.
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