1750 _ Before Industrial Revolution, atmosphere holds 280 parts per million of heat-trapping carbon dioxide (CO2).
1898 _ Swedish scientist Svante Ahrrenius calculates that CO2 from coal and oil burning will warm the planet.
1955 _ U.S. scientist Charles Keeling finds atmospheric CO2 has risen to 315 parts per million.
1971 _ First international conference on climate change is held in Sweden.
1986 _ Atmospheric CO2 reaches 350 ppm.
1988 _ NASA scientist James Hansen tells U.S. Congress global warming "is already happening now."
1988 _ U.N. creates the Intergovernmental Panel on Climate Change (IPCC), a clearinghouse for climate science.
1990 _ IPCC issues its First Assessment Report, noting Earth is warming.
1992 _ Climate treaty sets voluntary goals to lower CO2 and other greenhouse gas emissions.
1995 _ IPCC's Second Assessment Report says the "balance of evidence suggests a discernible human influence on global climate."
1997 _ Climate treaty parties approve Kyoto Protocol ordering emission cuts by industrial nations; approach rejected in advance by U.S. Senate.
1998 _ Warmest year globally since record-keeping began in mid-19th century.
2001 _ IPCC's Third Assessment Report cites "new and stronger evidence" that mankind is altering climate.
2001 _ U.S. President George W. Bush renounces Kyoto Protocol.
2004 _ Russia ratifies Kyoto Protocol, bringing it into force in February 2005.
2007 _ IPCC Fourth Assessment Report says most warming is "very likely" due to manmade emission. Report shows global temperatures rose 0.74 degrees C (1.3 degrees F) from 1906 to 2005.
2007 _ IPCC and former U.S. Vice President Al Gore win Nobel Prize for their climate work.
2007 _ In Bali, annual U.N. climate conference agrees on two-year timetable for successor agreement to Kyoto.
2009 _ Atmospheric CO2 hits a record 390 ppm.
2009 _ Delegates of 192 nations prepare for a crucial annual U.N. conference in Copenhagen, Denmark.