A Brief History of Climate Change

Today the Kyoto Protocol takes effect in an effort by 140 countries to reign in emissions of carbon dioxide and other greenhouse gases. The world's biggest emitter, the United States, is not participating, so the result is expected to be limited, reducing by about one-tenth a projected 30 percent rise in worldwide emissions between 1990 and 2010. [Full Story]

Key events in the story of climate change:

1750: Before Industrial Revolution, atmosphere holds 280 parts per million of heat-trapping carbon dioxide, later research determines.

1898: Swedish scientist Svante Ahrrenius warns carbon dioxide from coal and oil burning could warm the planet.

1955: U.S. scientist Charles Keeling finds atmospheric carbon dioxide has risen to 315 parts per million.

1988: NASA scientist James Hansen tells U.S. Congress global warming "is already happening now.''

1992: Climate treaty sets voluntary goals to lower carbon dioxide and other greenhouse gas emissions.

1995: U.N.-organized scientific panel says evidence suggests man-made emissions are affecting climate.

1997: Treaty parties approve Kyoto Protocol mandating emission cuts by industrial nations, an approach rejected in advance by U.S. Senate.

1998: Warmest year globally since record-keeping began in mid-19th Century.

2001: U.N. scientific panel concludes most warming likely due to man-made emissions; President Bush renounces Kyoto Protocol.

2004: Carbon dioxide reaches record 379 parts per million; Russia gives crucial ratification to Kyoto Protocol.

2005: Kyoto Protocol takes effect on Feb. 16.