A third of human population may be imperiled by 2070 as temperatures move beyond ‘climate niche’: Study

Climatic conditions in which human life has thrived have remained largely unchanged for thousands of years. But a new study warns that global warming could change this status quo in just a matter of another 50 years.

Research by scientists from China, USA and Europe published in the journal Proceedings of the National Academy of Sciences this week revealed that if global greenhouse gas emissions are not kept in check, parts of the planet, home to one-thirds of the human population, will become as hot as the hottest parts of the Sahara by 2070.

Historically, humans have largely thrived in narrow climate bands – a majority live in places where the mean annual temperature (MAT) is about 11-15°C, while a smaller population lives in areas where the average temperature is between 20-25°C. This trend has largely remained unchanged over the last 6000 years despite technological innovation and migration, according to the researchers. This comfort zone is what scientists refer to as the ‘climate niche’. “This strikingly constant climate niche likely represents fundamental constraints on what humans need to survive and thrive,” says Professor Marten Scheffer of Wageningen University, who coordinated the research with his Chinese colleague Xu Chi, of Nanjing University.

But, the study says, if emission levels continue to rise at the rate they are currently, the temperature experienced by an average person will rise by 7.5°C by 2070 – this is 2.3 times more than the expected mean global temperature rise. This rise would mean that 30% of the projected population (3.5 billion people) will live in areas with average temperatures greater than 29°C in the next 50 years. Currently these climatic conditions are present in only 0.8% of the global land surface, but could spread to 19% of the planet’s land area if emissions don’t fall.

“The coronavirus has changed the world in ways that were hard to imagine a few months ago and our results show how climate change could do something similar. Change would unfold less rapidly, but unlike with the pandemic, there would be no relief to look forward to: large areas of the planet would heat to barely survivable levels and they wouldn’t cool down again. Not only would this have devastating direct effects, it leaves societies less able to cope with future crises like new pandemics. The only thing that can stop this happening is a rapid cut in carbon emissions,” says Jens-Christian Svenning from Aarhus University, a co-author of the study.

A rapid reduction on greenhouse gas emissions could halve the number of people exposed to such heat, according to the study.

The study does take into account that some of the 3.5 billion people exposed to this change may seek to migrate. But a decision to migrate depends on a lot more than just the climatic conditions, and mitigation at a local level is one way to ease some of that pressure felt by those affected, according to the researchers. The study also takes into account other factors that make it impossible to foresee climate-driven redistribution of the human population such as political developments, socioeconomic conditions, and even the impact on mortality because of heatwaves in dense, already-hot places such as India. These are areas that require further study, the researchers say.

“This study underscores why a holistic approach to tackling climate change that includes adapting to its impacts, addressing social issues, building governance, and empowering development as well as compassionate legal pathways for those whose homes are affected, is crucial to ensuring a world in which all humans can live with dignity,” Scheffer says.

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