The fertility rate of half the world is now 2.1 or less — “the replacement rate of fertility” (the number that is consistent with a stable population). If current trends continue, sometime between 2020 and 2050 the world’s fertility rate will fall below the global replacement rate.
Mothers in developing countries today can expect to have three children. Their mothers had six.
Richard Tol collected data on climate and conflict in Europe over the past thousand years (”Climate Change and Violent Conflict in Europe over the Last Millennium“).
Until the mid-18th century, the correlation between the number of conflicts and the average temperature is continuously and significantly negative — lower temperatures mean more wars. The line remains close to the 95% confidence level, suggesting there is only one chance in 20 that it is an accidental, random effect. Then, suddenly, the negative correlation vanishes. (The line goes into positive territory, but not enough to be statistically meaningful.)
The researchers suggest that in the more remote past the effects of cold weather on harvests led to supply shortages, and that these increased the likelihood of people fighting over food and the land needed to produce it. They argue that the reason the relationship between warfare and cold vanishes in the mid-18th century is that this is the moment when the industrial revolution began. The food supply increased and improvements in transportationallowed food to be more easily shipped to areas of scarcity.
Farmers could more often produce reasonable yields during colder weather — and long-distance trade provided a buffer against crop failure.
“Cool heads or heated conflicts?,” The Economist