World population estimates

This article lists estimates of world population over the course of history and prehistory, as well as projections of future developments. In summary, estimates for the progression of world population since the late medieval period are in the following ranges:

Estimates for pre-modern times are necessarily fraught with great uncertainties, and few of the published estimates have confidence intervals; in the absence of a straightforward means to assess the error of such estimates, a rough idea of expert consensus can be gained by comparing the values given in independent publications. Population estimates cannot be considered accurate to more than two decimal digits; for example, world population for the year 2012 was estimated at 7.02, 7.06 and 7.08 billion by the United States Census Bureau, the Population Reference Bureau and the United Nations Department of Economic and Social Affairs, respectively, corresponding to a spread of estimates of the order of 0.8%.

Most published estimates of historical world population begin at "year zero" of the Common Era, when world population was in the nine digits (estimates range between 150 and 330 million).

Some estimates extend their timeline into deep prehistory, to "10,000 BC", i.e. the last glacial maximum, when world population estimates range roughly between one and ten million.

Estimates for yet deeper prehistory, into the Upper Paleolithic, are of a different nature. At this time human populations consisted entirely of non-sedentary hunter-gatherer populations, which fall into a number of archaic species or sub-species, some but not all of which may be ancestral to the modern human population due to possible archaic human admixture with modern humans taking place during the Upper Paleolithic. Estimates of the size of these populations are a topic of paleoanthropology. A late human population bottleneck is postulated by some scholars at approximately 70,000 years ago, during the Toba catastrophe, when the Homo sapiens population may have dropped to as low as between 1,000 and 10,000 individuals.

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