Guest Post by Willis Eschenbach

I stumbled across a paper called “Future of the human climate niche“, published in the Proceedings of the National Academy of Sciences. The abstract says (emphasis mine):

Abstract
All species have an environmental niche, and despite technological advances, humans are unlikely to be an exception. Here, we demonstrate that for millennia, human populations have resided in the same narrow part of the climatic envelope available on the globe, characterized by a major mode around ∼11 °C to 15 °C mean annual temperature (MAT).

Supporting the fundamental nature of this temperature niche, current production of crops and livestock is largely limited to the same conditions, and the same optimum has been found for agricultural and nonagricultural economic output of countries through analyses of year-to-year variation.

We show that in a business-as-usual climate change scenario, the geographical position of this temperature niche is projected to shift more over the coming 50 y than it has moved since 6000 BP. Populations will not simply track the shifting climate, as adaptation in situ may address some of the challenges, and many other factors affect decisions to migrate.

Nevertheless, in the absence of migration, one third of the global population is projected to experience a MAT >29 °C currently found in only 0.8% of the Earth’s land surface, mostly concentrated in the Sahara. As the potentially most affected regions are among the poorest in the world, where adaptive capacity is low, enhancing human development in those areas should be a priority alongside climate mitigation.

Well, that seemed kinda reasonable. After all, a mean average temperature (MAT) between 11 °C to 15 °C (52°F to 59°F) sounds comfortable, and I imagined it would be a fairly wide zone. And people tend to go where it’s comfortable.

So I decided to graph out just how that plays out around the globe … here’s that result. Upper graphic shows the whole planet, lower graphic shows just the land.

Figure 1. The “human climate niche” lies between 11°C (blue line) and 15°C (red line). Berkeley Earth data

YIKES! When the Abstract said a “narrow part of the climatic envelope”, they weren’t kidding. A skinny strip across the US, a skinny strip along the Andes, a narrow band from Europe to China, a tiny part of Africa and Australia … wow.

Of course, my first question was whether the problem was with my data. So I repeated the experiment with the CERES data.

Figure 2. The “human climate niche” lies between 11°C (blue line) and 15°C (red line). CERES data.

Well, slight differences, but basically the same.

So I thought, well, maybe they’re using some special dataset. So I checked the Supplementary Information and found that they use a dataset called the “WorldClim” data. I downloaded that, spent far too long trying to figure out how to import a “GeoTiff” file into R, and took a look.

Figure 3. The “human climate niche” lies between 11°C (blue line) and 15°C (red line). WorldClim data.

Aaaand … they all agree, within the usual differences in climate datasets.

Next, I looked at where people live on this wonderful planet. Here’s that chart. I’ve overlaid the WorldClim 11°C (white) and 15°C (yellow) lines on the graphic.

Figure 4. Log base 10 of population density per square kilometer.

As you might have guessed, the biggest population centers are in India and eastern China. Other populated spots are Europe, tropical Africa, southeast Asia, eastern Brazil, Indonesia, Mexico, and the eastern US.

And the crazy part?

Not one of those centers of dense population lies within their “human climate niche” … some are too cold, some are too hot. India, packed with people, has an average annual temperature of 27°. Canada and Russia are hopeless. And cold foggy England? Fuggeddaboutit!

Not sure I can say much more about that study … have I made some curious error? I don’t think so.

Onwards, ever onwards,

w.

PS—My usual request: When you comment please quote the exact words you are discussing. It avoids endless misunderstandings. Thanks.