In a new article in Nature Sustainability, Lenton and his research colleagues have analyzed settlement patterns against climate worldwide. The purpose has been to measure the human cost of global warming. They have not started from any extreme scenario, but a global warming of 2.7 °C – so roughly what we are steering towards today. What they find is that the warming is already causing 600 million people to live outside the climate niche that humanity throughout history has largely lived within. It can have dramatic consequences, says Professor Tim Lenton:
If we manage to limit warming to 1.5 degrees, a lot can be saved. But that is not what we are aiming for. Around 9 percent of the world’s population already lives outside this limit. By the end of the century, given that we do not change policy more drastically than the current climate targets, a third of the world’s population will do the same. By all accounts, it will have dramatic consequences for global food supply, migration and conflicts. It will affect us all, says Lenton.
We talk to
Tim Lenton is a professor at the University of Exeter and director of the Global Systems Institute.
<2°C: – First, can you briefly describe what you mean by climate niche?
Tim Lenton: – The term is about how human populations are dependent on a specific temperature and rainfall. This dependence has been remarkably similar over the millennia, and is usually around 12 degrees Celsius as the average annual temperature. If we draw a graph showing population plotted against these mean temperatures, the largest peak is around that temperature. There is also another “peak” on the graph around 25 degrees, which is mainly concentrated in areas with a monsoon climate. The population declines sharply at higher average temperatures. We define anything above 29 degrees as the average annual temperature as outside the niche.
– And the temperatures in between?
– They are usually more associated with drier climates. So here comes the precipitation.
– Life threatening
– What happens when, as you write in the article, two million people live outside this niche in 2030?
– As I said, places with a higher average temperature have usually had a low population. When people live in such conditions, they are primarily more exposed to extreme temperatures. We already know that high average temperatures correlate quite well with high extreme temperatures. Either very hot dry extremes or higher temperatures combined with high humidity. Such extreme temperatures can be harmful to health. At temperatures as low as 28 degrees Celsius, the effect of sweat to cool the body is less effective, when humidity is high. And at 35 degrees, the heat can become life-threatening, especially for vulnerable people.
But in addition to the threat to human health, the climate niche also says something about the availability of food and water. Livestock and arable crops also have climatic niches, and since most animals used for food are mammals, they mostly have the same niche as humans. All the research we have reviewed also shows that crops of typical food crops tend to reach peak productivity within the human niche.
– Skewedly distributed population growth
– According to the article, in 2030 there will be 1.2 million people living outside the climate niche due to temperature changes alone. But the number rises to two million when we take population changes into account. What do you mean by that?
– Most people probably know that the world’s population is still growing. Growth has slowed somewhat, but it is still increasing, especially in sub-Saharan Africa. This is an area of the world that is already hot. So you have people living in warm areas that warm up further, and we have population growth that is skewed towards warmer areas. All this contributes.
Nigeria is a classic example here. A place where the population is increasing, by the end of the century almost a billion people will live in this part of Africa. In countries that will be exposed to high extreme temperatures.
– But for those of us lucky enough to live in a cooler part of the world, will it matter as much? As long as we still get enough rain, anyway?
– Of course, those of us who live at the cooler end of the niche can be tempted to think that we will be better off. Especially since cold extremes are also harmful to human health, and they will be reduced. But I would encourage people to think a little more broadly. We live in a globalized economy, we face potentially massive humanitarian crises in the global south and the tropics. In addition, some of these areas are among the world’s granaries, where food is produced and exported to other parts of the world. In other words, this will have global consequences. We have to be in this together, whether we like it or not.
– What about climate change? Is there even a possibility here, with 2.7 degrees of warming?
– Climate adaptation is always a possibility. But our work shows that this primarily poses a serious threat to billions of people in the global south, and there the possibilities for adaptation are limited. One of the best options is migration.
Then we should think about it: Are we able to handle such a large-scale redistribution of the global population? I don’t quite see that we have a policy that recognizes this problem. Or that we take on the enormous challenge that awaits us in the future. That may be a reason in itself why we must do everything we can to limit global warming. If we limit the huge number of people exposed to dangerously high temperatures in the south and the tropics, we will reduce much of the damage potential. Meanwhile, rich countries must meet the frankly modest commitments to provide $100 million annually for adaptation efforts in the Global South.
– You have also researched tipping points before. And one of the factors you have studied is changes in monsoon patterns and the effect of rising temperatures on them. And several of the countries you mention as most vulnerable in the article – largely in such monsoon areas. Does this have the potential to confound the consequences dramatically?
– Yes. And as someone who works at tipping points, I really feel for the people who live in these densely populated regions. Should we find that we are passing a tipping point in the tropical monsoon systems in these densely populated areas, they will be exposed to extraordinary climate risk. This is our responsibility. We owe it to them to help deal with it.