When climate scientists warn about average temperature rise projections of two, three, or more degrees warming, that can be an abstract concept for most people. Most of us really can’t wrap our minds around the consequences of global temperature rise by such a seemingly small numerical value.
That is precisely why the scientific team gathered around the new paper, “Future of the human climate niche,” published in the Proceedings of the National Academy of Sciences, made it their goal to present the predicted warming in more familiar human terms.
The research team used data from UN population projections to map out how a three-degree warming scenario will translate into temperature changes for the world’s population. Unfortunately, we are currently on course for a 3 degrees C rise, regardless of the Paris agreement.
The results are grim: by 2070 more than three billion people will live in regions with the average temperature beyond 29 degrees C (84 degrees Fahrenheit). That temperature range is considered “near un-liveable“, and a stark difference from the temperature niche in which the human civilization has been developing for the last 6 millennia.
The areas with a mean annual temperature (MAT) of above 29 °C currently cover only 0.8 percent of the Earth’s land surface, with most of them belonging to the Sahara desert.
Such a drastic rise in MAT values is due to the fact that land warms at a faster rate than the ocean, meaning that 3-degree average warming will result in even more drastic warming in continental areas.
Most of the human population today lives in places where MAT is 11-15°C. A smaller proportion of the population lives in areas where MAT reaches 20-25°C. The latter group is the most vulnerable to the upcoming temperature rise, especially considering the fact that many of the countries that are to be affected are already struggling economically.
The study projects that the areas to be most affected include northern Australia, India, Africa, South America, and parts of the Middle East.
Tim Lenton, climate specialist and director of the global Systems Institute at the University of Exeter and a co-author of the study, summed it up for the BBC:
“The land warms up faster than the ocean so the land is warming more than three degrees. Population growth is projected to be in already hot places, mostly sub-Saharan Africa, so that shifts the average person to a hotter temperature. It’s shifting the whole distribution of people to hotter places which themselves are getting hotter and that’s why we find the average person on the planet is living in about 7C warmer conditions in the 3C warmer world.”
The poor regions are of the greatest concern, for at least two reasons. First and the most obvious, nations already struggling to cope will have a hard time mitigating all effects of extreme heat. Secondly, these are the places that are experiencing – and will continue to experience – population growth.
“For me, the study is not about the rich who can just get inside an air-conditioned building and insulate themselves from anything,” Lenton continues. “We have to be concerned with those who don’t have the means to isolate themselves from the weather and the climate around them.”
However, that doesn’t mean that the economically developed countries in temperate climates are safe.
The mean annual temperature also conditions the main pillars of the economy. Crop and livestock production is in a tight connection to the region’s climatic niche. As the study states, “the same optimum has been found for agricultural and nonagricultural economic output of countries through analyses of year-to-year variation.”
What it means is that the economic consequences of predicted 3-degree warming will not discriminate between the wealthier and the poorer nations. Everyone will experience hardships as the regions fall out of the environmental niche they have been adapted to for millennia.
Still, the point of the paper is not to instill the feeling of impending doom – it’s quite the opposite. Tim Lenton explained that the main takeaway is that any limitation of the degree of climate change could drastically reduce the number of people projected to fall victim to extreme heat.
“It’s about roughly a billion people for each degree of warming beyond the present. So for every degree of warming, we could be saving a huge amount of change in people’s livelihoods.”
Xu, C., Kohler, T. A., Lenton, T. M., Svenning, J.-C., & Scheffer, M. (2020). Future of the human climate niche. Proceedings of the National Academy of Sciences of the United States of America, 117(21), 11350–11355. https://www.pnas.org/content/117/21/11350
Climate change: More than 3bn could live in extreme heat by 2070. BBC. 5 May 2020. https://www.bbc.com/news/science-environment-52543589
Unsuitable for ‘human life to flourish’: Up to 3B will live in extreme heat by 2070, study warns. USA Today. 4 May 2020 https://www.usatoday.com/story/news/world/2020/05/04/world-heat-conditions-unlivable-global-warming-unabated/3063849001/