November 04, 2009
A UN conference in Copenhagen in December 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.
 | An Icy HeraldMelting glaciers are one visible effect of global warming - the phenomenon has been around for centuries (Photo: Shutterstock |
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 vapour 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 UN Framework Convention on Climate Change, which sets a non-binding goal of stabilising 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
A Group of Eight leaders agree industrialised nations should cut emissions on average by 80 percent by 2050 and limit warming to a maximum of 2 Celsius above pre-industrial times.
editor: Reuters
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