There’s a reason you can’t find polar bears in tropical areas or dormitories in the Arctic. Animals adapt to climate niches based on temperature and rainfall. People who make fire and air conditioning efficient may surpass our original niche, but a study of population distribution over the last, 6,000 years suggests more stability than expected for our preferred climate zones.
Unfortunately, the authors add, global warming has removed many areas outside of this niche, questioning the continued habitat of nearly 3 billion people. Dr. Chi Xu of Nanjing University used two distinct reconstructions of the distribution of the human population over 2,000 years ago and compared them with the average annual temperature (MAT) and the annual rainfall of those places, including nights and days.
Several brave souls lived in the Sahara and Greenland, according to the proceedings of the Jewish National Academy of Sciences. However, during the early development of agriculture, the vast majority of the world’s population lived in areas of 11-15 degrees Celsius (52-59 ° F) and 30-100 centimeters (12-40 inches) of rainfall, something that remains true today.
There has been some change in the intervening period – 300 years ago, Europe’s growing population meant the most common MAT for the world’s population was about 9 degrees Celsius (48 degrees Fahrenheit) but that was the exception. Both in ancient times and today, people living outside the 11-15 niche could live in more places with mats of 25 degrees Celsius (62-77°F) than in the 17-22 degree centigrade region (62-77 ° F).
The development of better heating and cooling systems has widened the human niche, but only for a minority. Global warming is turning it from curiosity to potential disaster. Using climate models with uninterrupted greenhouse gas emissions in 2070, Xu found that much of the world would still be in the niche at 11-15 degrees Celsius (52-59 degrees Fahrenheit) but it would not be the same place as it is today. In fact, the paper observes that “the geographical location of this temperature niche is expected to shift more over the next 50 years than last, 6,000.”
3.5 billion People have to adapt or move. For those living with mats of 13 degrees Celsius (55 degrees Fahrenheit), a shift to high-density teens may be manageable, but in the tropics, the population growth is greatest with MAT 25 ° C (77 ° F). The authors note, “In the absence of migration, one-third of the world’s population is expected to experience a mat> 29 degrees centigrade (64 degrees Fahrenheit), with only 0.6 percent of the Earth’s surface currently found, mostly concentrated in the Sahara.”
Forcing mass migration as sea levels rise, and which countries could take in these climate refugees, has attracted some media attention. However, Xu’s work suggests that flood numbers from their homes could be dwarfed by people evicted due to unbearable heat.