The current trajectory of climate change could put some 2 billion people at risk from extreme temperatures by the turn of the century, according to research published Monday in the journal Nature Sustainability.
International agreements have already set a goal of holding planetary warming below 1.5 degrees Celsius, a target that would require major reductions in greenhouse gas emissions in the coming decades.
About 9 percent of the global population, around 600 million people, fall outside of what researchers called a human climate niche, or the climatic range in which humans have historically been able to live comfortably.
Meanwhile, the status quo for emissions, projected to lead to around 2.7 degrees of warming, could displace as much as 39 percent of the global population from the niche by the final 20 years of the 21st century, according to researchers.
The study also estimated the lifetime emissions of about 3.5 average people under the current status quo, or 1.2 average U.S. citizens, will expose about one future person to unprecedented heat by the end of the century.
The countries most vulnerable to the impacts projected in the study are overwhelmingly in the global south, according to the research. The country facing the most affected citizens would be India, with more than 600 million people. In a scenario where warming is kept to 1.5 degrees, this drops to 90 million people.
Nigeria is the second most vulnerable, with more than 300 million people exposed to extreme heat under a 2.7-degree scenario, as opposed to less than 40 million in a 1.5-degree scenario. In Indonesia, 100 million people are at risk with 2.7 degrees, compared to less than 5 million with 1.5 degrees.
In addition to those countries, researchers found a 2.7-degree scenario would expose the entirety of certain countries, including Burkina Faso and Mali, to unprecedented heat.
