There ’s a reason you do n’t find polar bears in the tropics or sloths in the Arctic . Animals are accommodate to climatic niches based on temperature and rain . Mastering fire and air - conditioning allowed man to expand beyond our original ecological niche , but a study of population statistical distribution over the last 6,000 years suggests more stability than expected for our preferred mood zones . unluckily , the authors lend , world-wide warming is move many expanse outside this niche , shout out into question the continued habitableness of up to 3 billion citizenry ’s home .
Dr Chi Xuof Nanjing University used two self-governing reconstructions of the distribution of human populations 6,000 year ago and compare them with the mean annual temperature ( MAT ) and annual rainfall of those placement , include nights and days . A few braw soul inhabited the Sahara and Greenland , Xu account inProceedings of the National Academy of Sciences . However , during the early development of agriculture , the immense bulk of the citizenry on Earth lived in area with MATs of 11 - 15 ° degree centigrade ( 52 - 59 ° degree Fahrenheit ) and 30 - 100 centimeter ( 12 - 40 inches ) rain , something that remains true today .
The intervening point has see some shifts – 300 years ago , the prosperous universe of Europe mean the most rough-cut MAT for the world ’s universe was around 9 ° atomic number 6 ( 48 ° F ) but this was the exception . Both in ancient times and today , people living outside the 11 - 15 niche were more potential to be in place with a MAT of 25 ° C ( 77 ° F ) than in the 17 - 22 ° nose candy zone ( 62 - 77 ° atomic number 9 ) . The development of more ripe heating and cooling mechanisms has broadened the human niche , but only for a small minority .
Global thaw is turning this from a oddity to a possible disaster . Using models of climate in 2070 with unabated greenhouse gas expelling , Xu found plenty of the cosmos will still lie in the 11 - 15 ° C ( 52 - 59 ° F ) recess , but it wo n’t be the same lieu as today . Indeed , the newspaper observe that " the geographical position of this temperature recession is projected to shift more over the arrive 50 years than it has [ in the last 6,000 ] . ”
Up to 3.5 billion people will have to adjust or move . For those living with an MAT of 13 ° C ( 55 ° F ) , a duty period to the in high spirits teens may be manageable , but population growth is highest in the tropical region with MATs 25 ° C ( 77 ° F ) .
“ In the absence of migration , one - third of the world population is contrive to experience a MAT > 29 ° one C ( 84 ° F ) currently found in only 0.8 percent of the Earth ’s demesne control surface , mostly rivet in the Sahara , ” the author note .
The hypothesis of rising sea level forcing mass migration , and which commonwealth might take these climate refugees , get some media attending . However , Xu ’s work propose the figure flooded from their home plate could be dwarfed by those repel out by unbearable heat .
