20th century

== Earth at the end of the 20th century ==
Economic growth and technological progress had radically altered daily lives. Europe appeared to be at a sustainable peace for the first time in recorded history{{citation needed|date=January 2024}}. The people of the [[Indian subcontinent]], a sixth of the world population at the end of the 20th century, had attained an [[Partition of India|indigenous independence]] for the first time in centuries. China, an ancient nation comprising a fifth of the world population, was finally [[Chinese economic reform|open to the world]], creating a new state after the near-complete destruction of the old cultural order. With the end of colonialism and the Cold War, nearly a billion people in Africa were left in new nation states.

The world was undergoing its second major period of [[globalization]]; the first, which started in the 18th century, having been terminated by World War I. Since the US was in a dominant position, a major part of the process was [[Americanization]]. The influence of China and India was also rising, as the world's largest populations were rapidly integrating with the world economy.

[[Terrorism]], dictatorship, and the spread of [[nuclear weapon]]s were pressing [[global issues]]. The world was still blighted by small-scale wars and other violent conflicts, fueled by competition over resources and by ethnic conflicts.

Disease threatened to destabilize many regions of the world. New viruses such as the [[West Nile virus]] continued to spread. [[Malaria]] and other diseases affected large populations. Millions were infected with HIV, the virus which causes AIDS. The virus was becoming an [[AIDS in Africa|epidemic in southern Africa]].

Based on research done by climate scientists, the majority of the scientific community consider that in the long term environmental problems pose a serious threat.<ref>{{cite book | title=Extreme and Irreversible Effects | at=[http://www.grida.no/climate/ipcc_tar/wg2/679.htm Sec 19.6.] | chapter-url=http://www.grida.no/climate/ipcc_tar/wg2/657.htm | chapter=Ch. 19. Vulnerability to Climate Change and Reasons for Concern: A Synthesis | author=Smith, J.B. | display-authors=etal | access-date=2014-07-10 | archive-url=https://web.archive.org/web/20161018213321/http://www.grida.no/climate/ipcc_tar/wg2/657.htm | archive-date=2016-10-18 | url-status=dead }}, in {{harvnb|IPCC TAR WG2|2001}}</ref> One argument is that of [[global warming]] occurring due to human-caused emission of [[greenhouse gas]]es, particularly [[carbon dioxide]] produced by the burning of [[fossil fuel]]s.<ref>{{Harvnb|IPCC AR5 WG1|2013}}, [https://www.ipcc.ch/site/assets/uploads/2018/02/WG1AR5_SPM_FINAL.pdf "Summary for Policymakers, Observed Changes in the Climate System"], pp. 10–11: "Total radiative forcing is positive, and has led to an uptake of energy by the climate system. The largest contribution to total radiative forcing is caused by the increase in the atmospheric concentration of CO<sub>2</sub> since 1750." (p 11). "From 1750 to 2011, CO<sub>2</sub> emissions from fossil fuel combustion and cement production have released 375 [345 to 405] GtC to the atmosphere, while deforestation and other land use change are estimated to have released 180 [100 to 260] GtC." (p. 10).</ref> This prompted many nations to negotiate and sign the [[Kyoto Protocol|Kyoto treaty]], which set mandatory limits on carbon dioxide emissions.

[[World population]] increased from about 1.6&nbsp;billion people in 1901 to 6.1&nbsp;billion at the century's end.<ref>{{cite web|title=World Population: Historical Estimates of World Population |url=https://www.census.gov/population/international/data/worldpop/table_history.php|publisher=United States Census Bureau|date=December 19, 2013|access-date=2015-01-09}}</ref><ref>{{cite web |url=https://www.census.gov/population/international/data/worldpop/table_population.php|title=World Population: Total Midyear Population for the World: 1950–2050|publisher=United States Census Bureau |date=December 19, 2013 |access-date=2015-01-09}}</ref>