TIMELINE: How the world found out about global warming

Reuters 4 Nov 09;

(Reuters) - A U.N. conference in Copenhagen next month is due to agree a new pact to combat global warming after mounting evidence that human activity is disrupting the climate.

The following is a timeline of the discovery of global warming.

300 BC - Theophrastus, a student of Greek philosopher Aristotle, documents that human activity can affect climate. He observes that drainage of marshes cools an area around Thessaly and that clearing of forests near Philippi warms the climate.

17th century - Flemish scientist Jan Baptista van Helmont discovers that gases different from normal air -- carbon dioxide -- are given off by burning charcoal.

17th century - The Industrial Revolution starts, bringing rising use of fossil fuels

1824 - Frenchman Joseph Fourier suggests that something in the atmosphere is keeping the world warmer than it would otherwise be -- a hint at the greenhouse gas effect.

1837 - Swiss naturalist Louis Agassiz presents evidence of big past changes in Alpine glaciers -- pointing to ancient Ice Ages and showing that the climate has not always been stable.

1860s - Irish scientist John Tyndall shows that molecules of gases such as water vapor and carbon dioxide trap heat. He wrote that changes "could have produced all the mutations of climate which the researches of geologists reveal."

1896 - Sweden's Svante Arrhenius becomes the first to quantify carbon dioxide's role in keeping the planet warm. He later concluded that burning of coal could cause a "noticeable increase" in carbon levels over centuries.

1957-58 - U.S. scientist Charles Keeling sets up stations to measure carbon dioxide concentrations in the atmosphere at the South Pole and at Mauna Loa, Hawaii. The measurements have shown a steady rise.

1965 - U.S. President Lyndon Johnson tells Congress: "This generation has altered the composition of the atmosphere on a global scale through...a steady increase in carbon dioxide from the burning of fossil fuels."

1988 - British Prime Minister Margaret Thatcher tells the United Nations: "The problem of global climate change is one that affects us all and action will only be effective if it is taken at the international level. It is no good squabbling over who is responsible or who should pay."

1988 - The United Nations sets up the Intergovernmental Panel on Climate Change (IPCC) to assess the scientific evidence.

1992 - World leaders agree the U.N. Framework Convention on Climate Change, which sets a non-binding goal of stabilizing greenhouse gas emissions by 2000 at 1990 levels -- a target not met overall. 1995 - The IPCC concludes for a first time that humans are causing global warming, saying: "the balance of evidence suggests a discernible human influence on global climate."

1997 - The Kyoto Protocol is agreed in Japan; developed nations agree to cut their greenhouse gas emissions on average by at least 5 percent below 1990 levels by 2008-12. The United States stays out of the deal.

2001 (January) - The IPCC concludes that it is "likely" -- or 66 percent probable -- that human activities rather than natural variations are the main cause of recent warming.

2001 (June) - President George W. Bush notes the U.S. National Academy of Sciences says greenhouse gases are rising "in large part due to human activity." He adds: "Yet, the Academy's report tells us that we do not know how much effect natural fluctuations in climate may have had on warming. We do not know how much our climate could, or will change in the future."

2007 - The IPCC says that it is "very likely" -- at least 90 percent certain -- that humans are to blame for most of the observed warming trend of the past 50 years. It also said that warming of the planet was "unequivocal."

2009 - Group of Eight leaders agree industrialized nations should cut emissions on average by 80 percent by 2050 and limit warming to a maximum of 2 Celsius above pre-industrial times.