Human Population

The growth rate of the global human population achieved a maximum during the late 1960s, when it was 2.1% per year. If sustained, this rate was capable of doubling the population in only 33 years. This rate of increase slowed somewhat to 1.5% per year in the 1999, equivalent to a doubling time of 47 years, and in 2002 had slipped to about 1.3%. Even at today's comparatively modest growth rates, the human population increases by about 80 million people each year.

Reasonable predictions can be made of future increases of the human population. The predictions are based on assumptions about the factors influencing changes in the size of populations, for example in the rates of fecundity, mortality, and other demographic variables. Of course, it is not possible to accurately predict these dynamics because unanticipated changes, or "surprises," may occur. For example, a global war could have an enormous influence on human demographics, as could the emergence of new diseases. AIDS is an example of the latter effect, because this lethal viral disease was unknown prior to the early 1980s.

As a result of these uncertainties, it is not possible to accurately forecast the future abundance of human beings. However, reasonable assumptions about demographic parameters can be based on recent trends in birth and death rates. Similarly, changes in the carrying capacity of Earth's regions for the human economy can be estimated from recent or anticipated advances in technology and on predictions of environmental changes that may be caused by human activities. These types of information can be used to model future populations of human beings.

A typical prediction of recent population models is that the global abundance of human beings could reach about seven billion by 2011 or 2015, depending on birth rate variations, and 8.9 billion by 2050. Models tend to predict that the human population could stabilize at about 10–12 billion. In other words, the global abundance of human beings will probably double again before it stabilizes. This prediction is likely to be fulfilled unless there is an unpredicted, intervening catastrophe such as a collapse of the carrying capacity of the environment, an unprecedented and deadly pandemic, or a large-scale nuclear war.