21st century
The period from January 1, 2001, through December 31, 2100, in the Gregorian calendar. It is the current century as of 2026.
September 11 attacks: A series of coordinated terrorist attacks by al-Qaeda against the United States on September 11, 2001. The attacks reshaped security policy and international conflict early in the century.
Fourth Industrial Revolution: A proposed period of technological change marked by the convergence of digital, physical, and biological systems. It frames the century's rapid integration of automation, data, and biotechnology.
Gregorian calendar: The solar calendar introduced by Pope Gregory XIII in 1582 and used internationally for civil purposes. Its year numbering defines the century's exact boundaries.
Global warming: The long-term rise in Earth's average surface temperature, primarily caused by human greenhouse-gas emissions. Future emissions and policy choices will determine how severe warming becomes before 2100.
20th century: The period from January 1, 1901, through December 31, 2000, in the Gregorian calendar. Its end date clarifies why the 21st century began in 2001.
2008 financial crisis: A global financial crisis triggered by the collapse of the United States housing bubble and related financial failures. Its recession and policy responses influenced economies and politics across the century.
Climate change: Long-term changes in Earth's temperatures and weather patterns, driven today mainly by human greenhouse-gas emissions. Warming and its effects have become defining environmental pressures of the century.
Century: A period of 100 years, commonly numbered from the first year through the hundredth year. A century's ordinal numbering places the 21st century in 2001–2100.
Energy transition: The shift from fossil fuels toward low-carbon energy sources and systems. Its speed will shape emissions, energy security, and economic change throughout the remaining decades.
22nd century: The period from January 1, 2101, through December 31, 2200, in the Gregorian calendar. It begins immediately after the 21st century's final day.