Global Heating Will Push Billions Outside ‘Human Climate Niche,’ Study Warns

For hundreds, possibly thousands, of years humans have lived inside a relatively comfortable “climate niche” wherein a large portion of the world’s population have mostly enjoyed liveable temperatures and infrequent extreme weather events. Conditions that have not only been within a healthy temperature range for humans, but for the plants, animals and ecosystems of our planet.

A new study estimates that billions of people will be driven out of this climate niche by global heating, where they will be vulnerable to more severe and frequent extreme weather and unparalleled high temperatures.

Today, nine percent of the world’s population — 600 million people — have already been pushed outside of the niche by climate change.

“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 study’s authors wrote.

The researchers added that limiting global warming to 1.5 degrees Celsius, or 2.7 degrees Fahrenheit — a level many scientists believe is now unattainable because of the trajectory we are on due to human activities — would result in approximately five times fewer people exposed to the more extreme temperatures.

The study, “Quantifying the human cost of global warming,” was published in the journal Nature Sustainability.

The authors said that, by the close of this century, the lifetime carbon emissions of about 3.5 average people across the world — or approximately 1.2 average U.S. citizens — will result in the exposure of one future human being to temperatures never before seen. And not just any person, but someone living in a part of the world where current emissions are at about 50 percent of the average for the rest of the planet. This demonstrates the necessity for policy changes to mitigate the consequences of climate change disparities for humanity as a whole, the authors wrote.

“The costs of global warming are often expressed in financial terms but our study highlights the phenomenal human cost of failing to tackle the climate emergency,” said professor Tim Lenton, director of the Global Systems Institute and chair in Climate Change and Earth System Science at the UK’s University of Exeter, who was also the lead author of the study, as The Guardian reported. “Economic estimates almost always value the rich more than the poor, because they have more assets to lose, and they tend to value those alive now over those living in the future. We’re considering all people as equal in this study.”

The research team said as many as one billion people could migrate to areas still within the climate niche, but those places would also experience droughts and heat waves more frequently.

If humans were able to limit global heating to 2.7 degrees Fahrenheit, 80 percent fewer people — that’s 400 million — would be forced outside the climate niche, reported The Guardian.

“For every 0.1°C of warming above present levels, about 140 million more people will be exposed to dangerous heat. This reveals both the scale of the problem and the importance of decisive action to reduce carbon emissions. Limiting global warming to 1.5°C rather than 2.7°C would mean five times fewer people in 2100 being exposed to dangerous heat,” Lenton said, according to Earth.com.

In countries that are already experiencing extreme temperatures and have large amounts of people, most of the population will be forced outside of the climate niche. Nigeria and India will be the most affected countries, with Pakistan, the Philippines and Indonesia also suffering serious impacts.

“Such high temperatures [outside the niche] have been linked to issues including increased mortality, decreased labour productivity, decreased cognitive performance, impaired learning, adverse pregnancy outcomes, decreased crop yield, increased conflict and infectious disease spread,” said professor Chi Xu of the School of Life Sciences at China’s Nanjing University, who was also part of the research team, as The Guardian reported.

The study found that most humans live in parts of the globe with average yearly temperatures from about 55.4 to 77 degrees Fahrenheit. Conditions hotter or colder than that are too extreme.

“Most of these people lived near the cooler 13°C peak of the niche and are now in the ‘middle ground’ between the two peaks. While not dangerously hot, these conditions tend to be much drier and have not historically supported dense human populations,” Xu said, as reported by Earth.com.

If the planet continues to heat up, population increases combined with rising temperatures would lead to 3.7 billion people living outside the climate niche by the year 2090.

“The climate niche describes where people flourish and have flourished for centuries, if not millennia in the past. When people are outside [the niche], they don’t flourish,” said Lenton, as The Guardian reported.

In the extreme scenario in which the climate were to rise by 6.48 degrees Fahrenheit, nearly half of Earth’s population would be pushed outside the life-sustaining niche.

Lenton said the quickest and most realistic way for humans to adapt to more extreme temperatures is to ramp up the number of urban green spaces.

“This can shave 5C off extreme temperatures and provide shade – that’s huge,” Lenton said, according to The Guardian.