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900-1300: The Medieval Warm Period brings warm weather to Europe, thanks to an unusually strong North Atlantic Oscillation bringing in extra heat.
1350-1850:TheLittle Ice Agechills parts of the northern hemisphere.
1709:As the Little Ice Age comes to an end, Europe experiences afreakishly cold winter.
1827:French polymath Jean-Baptiste Fourier predicts an atmospheric effect keeping the Earthwarmer than it would otherwise be. He is the first to use a greenhouse analogy.
1863:Irish scientistJohn Tyndallpublishes a paper describing how water vapour can be a greenhouse gas.
1890s:Swedish scientistSvante Arrheniusand an American, P C Chamberlain, independently consider the problems that might be caused by CO2building up in the atmosphere. Both scientists realise that the burning of fossil fuels could lead to global warming, but neither suspects the process might already have begun.
1890s to 1940:Average surface air temperatures increase by about 0.25 °C. Some scientists see the AmericanDust Bowlas a sign of thegreenhouse effectat work.
1940 to 1970:Worldwide cooling of 0.2°C Scientific interest in greenhouse effect wanes. Some climatologistspredict a new ice age.
1957:US oceanographer Roger Revelle warns that humanity is conducting a "large-scale geophysical experiment" on the planet by releasing greenhouse gases. ColleagueDavid Keelingsets up first continuous monitoring of CO2levels in the atmosphere. Keeling soon finds a regularyear-on-year rise.
1970s:Series of studies by the US Department of Energy increases concerns about future global warming.
1979:First World Climate Conference adopts climate change as major issue and calls on governments "to foresee and prevent potential man-made changes in climate."
1985:First major international conference on the greenhouse effect at Villach, Austria, warns that greenhouse gases will "in the first half of the next century, cause a rise of global mean temperature which is greater than any in man's history." This could causesea levelsto rise by up to one metre, researchers say. The conference also reports that gases other than CO2, such asmethane,ozone,CFCsandnitrous oxide, also contribute to warming.
1987:Warmest year since records began. The 1980s turn out to be the hottest decade on record, with seven of the eight warmest years recorded up to 1990. Even the coldest years in the 1980s were warmer than the warmest years of the 1880s.
1988:Global warming attracts worldwide headlines after scientists at Congressional hearings in Washington DC blame major US drought on its influence. Meeting of climate scientists in Toronto subsequently calls for 20% cuts in global CO2emissions by the year 2005. UN sets up theIntergovernmental Panel on Climate Change(IPCC) to analyse and report on scientific findings.
1990:Thefirst report of the IPCCfinds that the planet has warmed by 0.5°C in the past century. IPCC warns thatonly strong measuresto halt rising greenhouse gas emissions will prevent serious global warming. This provides scientific clout for UN negotiations for a climate convention. Negotiations begin after the UN General Assembly in December.
1991:Mount Pinatubo erupts in the Philippines, throwing debris into the stratosphere thatshields the Earth from solar energy, which helpsinterrupt the warming trend. Average temperatures drop for two years before rising again. Scientists point out that this event shows how sensitive global temperatures are to disruption.
1992:Climate Change Convention, signed by 154 nationsin Rio, agrees to prevent "dangerous" warming from greenhouse gases and sets initial target of reducing emissions from industrialised countries to 1990 levels by the year 2000.
1994:The Alliance of Small Island States - many of whom fear they willdisappear beneath the wavess sea levels rise - adopt ademand for 20% cuts in emissionsby the year 2005. This, they say, will cap sea-level rise at 20 centimetres.
1995:The hottest year recorded to date. In March, the Berlin Mandate is agreed by signatories at thefirst full meeting of the Climate Change Conventionin Berlin. Industrialised nations agree on the need to negotiate real cuts in their emissions, to be concluded by the end of 1997.
In November, theIPCC statesthat current warming "is unlikely to be entirely natural in origin" and that "the balance of evidence suggests a discernible human influence on global climate".Its reportpredicts that, under a "business as usual" scenario, global temperatures by the year 2100 will have risen by between 1°C and 3.5°C.
1996:At thesecond meeting of the Climate Change Convention, the US agrees for the first time to legally binding emissions targets and sides with the IPCC against influential sceptical scientists. After a four-year pause, global emissions of CO2resume their steep climb, and scientists warn that most industrialised countrieswill not meet Rio agreementto stabilise emissions at 1990 levels by the year 2000.
1997:Kyoto Protocolagrees legally binding emissions cuts for industrialised nations, averaging 5.4%, to be met by 2010. The meeting also adopts a series of flexibility measures, allowing countries to meet their targets partly bytrading emissions permits,establishing carbon sinks such as foreststo soak up emissions, and by investing in other countries. The precise rules are left for further negotiations. Meanwhile, the US government says it will not ratify the agreement unless it sees evidence of "meaningful participation" in reducing emissions from developing countries.
1998:Follow-up negotiationsin Buenos Airesfail to resolve disputes over the Kyoto "rule book", but agree on adeadline for resolutionby the end of 2000. 1998 is thehottest yearin the hottest decade of the hottest century of the millennium.
2000:IPCC scientists re-assess likely future emissions andwarnthat,if things go badly, the world couldwarm by 6°C within a century. A series ofmajor floodsaround the worldreinforce public concernsthat global warming is raising the risk ofextreme weather events. But in November,crunch talksheld in The Hague to finalise the "Kyoto rule book" fail to reach agreement after EU and US fall out. Decisions postponed until at least May 2001.
2001:The new US president, George W Bush,renounces the Kyoto Protocolbecause he believes it willdamage the US economy. After some hesitation, other nations agree togo ahead without him. Talks inBonn in JulyandMarrakech in Novemberfinally conclude the fine print of the protocol. Analysts say that loopholes have pegged agreed cuts in emissions from rich-nation signatories to less than a third of the original Kyoto promise. Signatory nations urged to ratify the protocol in their national legislatures in time for it to come into force before the end of 2002.
2002:Parliaments in the European Union, Japan and others ratify Kyoto. But the protocol'scomplicated rulesrequire ratification by nations responsible for 55% of industrialised country emissions, before it can come into force. AfterAustralia joins the US in reneging on the deal, Russia is left to make or break the treaty, buthesitates. Meanwhile, the world experiences thesecond hottest year on recordand Antarctica's Larsen B ice sheetbreaks up.
2003:Globally it is the third hottest year on record, but Europe experiences the hottest summer for at least 500 years, with anestimated 30,000 fatalitiesas a result. Researchers later conclude thatclimate change at least doubled the risk of the heatwave happening. Extreme weather costs an estimated record of $60 billion this year. 2003 also sees a marked acceleration in the rate of accumulation of greenhouse gases. Scientists are uncertain if it is a blip or a new, more ominous trend. Meanwhile Russiablows hot and coldoverKyoto.
2004:Adeal is struckon Kyoto. President Putin announces in May thatRussia will back the Protocol. On 18 November, the Russian parliamentratifies the protocol, paving the way for it to come into force in 2005. A studylinks the 2003 heatwave to global warming. Hollywood blockbusterThe Day After Tomorrowbases its plot on anexaggerated climate change scenario.
2005:On 16 February, the Kyoto Protocol comes into force. In December,Kyoto signatories agreeto discuss emissions targets for the second compliance periodbeyond 2012, while countries without targets, including the US and China, agree to a "non-binding dialogue" on their future roles in curbing emissions. Europelaunches its Emissions Trading Scheme, despitecriticism of the idea.
2005 is the second warmest year on record. Researchers link warming to arecord US hurricane season,accelerated meltingfArctic sea iceandSiberian permafrost. At a pivotal climate meeting held in Exeter, UK, scientists warn that the west Antarctic ice sheet isstarting to collapse.
2006:The Stern Report, commissioned by the UK government, argues that thecosts of coping with climate changewill begreater than the costs of preventing it. Al Gore's climate change filmAn Inconvenient Truthbecomes abox-office hit. Carbon dioxide emissions are found to be risingfaster than in the 1990s, and new evidence bolsters theiconic"hockey stick" graph. The US Environmental Protection Agency istaken to the Supreme Courtover its refusal to regulate CO2emissions. US agencies,including NASA, are accused oftrying to censor climate experts.
2007:The fourth Assessment Report of the IPCC places theblame for global warmingirmly on humankind, estimates thecost of stabilising greenhouse gasesat $1830 billion, and calls for governments to beginplanning adaptive measures. Some of the most extreme scenarios areleft outof the report, leading to accusations that it has beenwatered down. The synthesis report warns of "abrupt and irreversible" climate change.
Al Gore and the IPCC areawarded the Nobel Peace Prize, while a UK judge criticisesAn Inconvenient Truthfor containing nine "factual inaccuracies". TV documentaryThe Great Global Warming Swindlealleges that climate science isdeeply flawed– the programme is later found to havemisrepresented the scienceand interviewed researchers complain to the British watchdog for broadcasting standards, Ofcom. In April the US Supreme Court rules that the EPAdoes have the authorityto regulate carbon dioxide emissions.
Measurements of solar activity show that it has declined since the 1980s,debunking the claimthat it is responsible for global warming. At the annual UN climate summit held in December in Bali, government representatives from around the worldagree a timetableto establish a post-2012 replacement for the Kyoto protocol. The United States delegation is publicly booed, then agrees to the pledge at the eleventh hour.
2008:The polar bear islisted on the US endangered species act, because of the risk to its habitat from climate change. Alaskathreatens to sueover the decision. The World Conservation Union finds thatthousands of speciesare at risk from climate change.
Barack Obamabecomes president of the United States, promisingincreases in science funding, especially forclimate change and energy technology. He appoints Nobel laureate winner and renewables expert Steve Chuas energy secretary.
2009:Governments, including the US, prepare to negotiate a successor to the Kyoto Protocol at a conference in December. Eric Steig and colleagues show that Antarctica iswarming. A thin strip of iceprotecting the Wilkins ice sheetrom collapsebreaks apart, hastening the sheet's demise – while the Arctic continues to warmmuch faster than expected. A major study suggests that humanity can emitno more than 1 trillion tonnes of carbon, if we are to avoid temperature rises of 2°C or more.
Indigenous peoples from around the world meet in Alaska to agree a common position on climate change. Italy and Switzerland agree to redraw their borderin response to melting glaciers.