Road to COP26: Global warming but local heat exposure

What climate change means for India’s and Africa’s growing populations – Tamir Klein

Tamir Klein

Climate change is here and is not showing any sign of moving away from the headlines. Headlines which come from every point on the globe, showing that the impact is indeed global. Wildfires in Australia are followed by heatwaves in North America, and so forth. However, as ecologists, we know that impacts are rarely truly balanced, nor symmetrical. For example, while plants and animals living in a valley might experience evolving conditions that become too hot for them, others living at high elevations can expand into new grounds that gradually become habitable. Being a tree eco-physiologist, I’ve seen the same logic in action with tree species distribution across latitudes: while the southern Mediterranean becomes too hot and dry for a pine species, the northern Mediterranean now offers good conditions for its expansion.

If the above principle holds for trees, there is no reason it should not be true for people. So I thought, when I called my friend and colleague, Prof. Bill Anderegg of the University of Utah. Both of us were working from home under the COVID19 restrictions, and at some level, the mind was free to ask more general questions, unrelated to the trees and forests we both enthusiastically study. Fortunately, Bill agreed with me that we can apply the very same tools we use to study forest sensitivity to climate change, to ask similar questions on human populations. Basically, what we asked was how would human exposure to heat look like at the end of this century.

Global warming is ubiquitous, and although some regions, e.g. Greenland, warm up faster than others, differences are still within the same order of magnitude. The fact that temperature generally decreases with latitude has also been known for centuries: The equator is warmer than mid-latitude regions, which, in turn, are warmer than the poles. And so some countries are warmer than others; a fact that we love to take advantage of when we plan our next overseas vacation (or used to before the COVID19…). What we didn’t know was how strongly human population growth interacts with these changes to act like a high-speed accelerator. Bill and I found that the fast population growth in already-hot countries make heat exposure highly unbalanced. The results of our study were recently published in the paper “A vast increase in heat exposure in the 21st century is driven by global warming and urban population growth”.

Global hotspots of increased exposure of human population to heat at the end of this century, compared to the beginning of the century. For example, yellow indicates 10 million people, whereas dark red indicates 40 million people. Analyses are based on climate change projections and the shared socioeconomic pathway (SSP3) scenario.

In short, what the climate change and population models show is that cities in Africa, India, and the Middle East will become exceedingly more vulnerable to heat during this century than anywhere else. It is in these low- and mid-latitude cities that hundreds of millions of people will be joining the circle of exposure to mean monthly temperatures over 35   ͦC (see Figure). If you are living outside of these regions, should you worry? The answer is probably yes! While adaptation could help relieve the heat for some of these people, e.g. using air conditioning, not all of the populations, living in some of our planet’s poorest countries, will be able to cope. In turn, these will seek other solutions, leading to a climate refugee crisis as inhospitable lands force those to leave their homes. But it’s not all bad. The good news is that things we change today can dramatically ease the heat exposure in years to come. Using scenarios of more sustainable population growth on the one hand, and of climate change mitigation on the other hand, yielded significantly lower impacts, even in India and Africa. These options should be on the table for policymakers in COP26 in Glasgow and everywhere.

Dr. Tamir Klein,

Weizmann Institute of Science

http://www.weizmann.ac.il/plants/klein/

For more information on this year’s COP26 meeting, read the handy BES Guide to COP26.

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