The Human Climate Niche

Every so often, I spot an unfamiliar word or phrase in the jargon of climate science.  One such term that caught my attention this past week is “climate niche.”  To the best of my present awareness, the term first appeared in a 2019 paper written by an international team headed by Chi Xu and published in Proceedings of the National Academy of Sciences.  The abstract of this paper begins with the rather ominous phrase “All species have an environmental niche, and despite technological advances, humans are unlikely to be an exception.”  The scientists involved in this study dug through historical climate data and drew the conclusion that most human activity, especially most of the agriculture associated with human activity, has taken place in areas where the mean annual temperature varies between 11ºC and 15ºC (52ºF and 59ºF).  There is a second, smaller niche between 20ºC to 25ºC (68ºF to 77ºF), where people in hot climates have gathered around areas with abundant water.  This pattern has remained consistent for 6000 years; in other words, humanity has had definite preferences where climate is concerned.  But of course, there is a catch.  Some regions that have fallen safely within these niches for millennia might not do so for much longer if the planet continues to warm.

The subject of climate niches garnered further attention this past week when a team comprised mostly of authors of the 2019 paper published a follow-up in Nature Sustainability.  This paper focuses on the human cost of population centers falling beyond the range of our climate niches.  The authors focus on people who, if they stay where they are, will find themselves living in an area with a mean average temperature of 29ºC (84ºF) — above the edge of the warm niche described in 2019, and warmer than any significant population center has ever consistently experienced.  Basically, given no change in current emissions policies worldwide, a median projected temperature increase of 2.7ºC (4.9ºF) by the end of this century will put one third of the world’s population above the 29ºC threshold.  This number would be substantially reduced if emissions are reduced, but the number most likely will not go down to zero.  

So what happens?  Some people, mostly in the tropics, will just have to get used to more frequent and dangerous heat.  Or perhaps they’ll have to deal with less water, or less ability to grow crops or make a living.  Perhaps they’ll have to deal with all of the above, plus rising sea levels if they live on a coast or more powerful storms when they do get rain.  Or, perhaps, they’ll need to move.  But to where?  And how warmly will they be welcomed?  This is why the cost of adapting to the world’s changes should not be taken lightly.  The old adage “an ounce of prevention is worth a pound of cure” applies here.