The United States Census Bureau has estimated the human population of the world to be 6,827,700,000, as of
17 June 2010. Earlier the United Nations estimated the Earth's human population to be 6,800,000,000 in 2009. The world population has been growing continuously since the end of the Black Death around 1400.
The fastest rates of world population growth (increases above 1.8% per year) were seen briefly during the 1950s then for a longer period during the 1960s and 1970s (see graph). The 2008 rate of growth has almost halved since its peak of 2.2% per year, which was reached in 1963.
Annual births have leveled at about 134 million per year since their peak at 163 million in the late 1990s and are expected to remain constant. However, deaths are only around 57 million per year, and are expected to increase to 90 million by 2050. Because births outnumber deaths, the world's population is expected between 2040 and 2050.
The rapid increase in human population over the course of the 20th century has raised concerns about whether Earth is experiencing overpopulation. The scientific is that the current population expansion and accompanying increase in usage of resources are linked to threats to the ecosystem, such as rising levels of atmospheric carbon dioxide, global warming, and pollution.