Timeline

1898: Swedish scientist Svante Ahrrenius calculates that CO2 from coal and oil burning will warm the planet.

1971: First international conference on climate change is held in Sweden.

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, 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.

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 report cites “new and stronger evidence” that humankind is altering climate.

2001: U.S. President George W. Bush renounces Kyoto Protocol.

2007: IPCC report says most warming is “very likely” due to human-caused emission. Report shows global temperatures rose 1.3 degrees Fahrenheit from 1906 to 2005.

2007: In Bali, annual U.N. climate conference agrees on two-year timetable for successor agreement to Kyoto.

2009: Delegates of 192 nations prepare for a crucial annual U.N. conference in Copenhagen, Denmark.

Associated Press