Most discussions around future climate change focus on average global temperature (AGT), which is an awful metric when it comes to communicating climate risks. After all, do numbers like "1.5" or even "2.7" really trigger a "red alert" risk response? Probably not.
That's why Tim Lenton's (et al) new paper "Quantifying the Human Cost of Global Warming" is important and useful. The goal of the paper (and it's a challenging one!) is to quantify the extent to which rising global temperatures will push humans outside the temperature "niche" to which we've gravitated over long periods of time, exposing humans to challenging local conditions (defined as more than 29 degrees C of local mean annual temperature), as well as Wet Bulb Temperatures of more than 28 degrees C). From the standpoint of overall potential climate risks, the paper's conclusions are alarming indeed. Here's the short story:
While today's today's 1.2 degrees of AGT has put 9% of people (600 million) outside the niche, by 2080-2100, assuming 2.7 degrees of AGT, roughly a third of the world's population is expected to be outside the niche. And that's not even close to the potential "worst case."
I've attached 3 graphics from the Lenton article that I think are insightful:
1) outcomes associated with the IPCC's multiple temperature scenarios;
2) Mapped exposure to dangerous heat at 1.5 and 2.7 degrees;
3) Country-level exposure to dangerous heat at 1.5 and 2.7 degrees based on absolute population, and % of a country's landmass. The graphics and numbers are staggering!
Imagine the disruptiveness of what's being described, not only to things like worker productivity, but to internal as well as international migration, the potential for local and global conflict, among MANY other potential implications. And that's not even getting into the challenges of providing the necessary energy for air-conditioning in the face of such changes.
No one should mistake the paper's conclusions for a prediction. There are plenty of uncertainties embedded in the paper's conclusions, ranging from climate change itself to policy responses and technology innovation, just to name a few areas of radical uncertainty. But it is a useful way of getting one's head around just how disruptive climate change is likely to be.
Graphics source: Lenton et al, Quantifying the human cost of global warming (2023).