Reported by New Scientist, May 13th, 2009
1350-1850: The Little Ice Age chills parts of the northern hemisphere.
1709: As the Little Ice Age comes to an end, Europe experiences a freakishly cold winter.
1827: French polymath Jean-Baptiste Fourier predicts an atmospheric effect keeping the Earth warmer than it would otherwise be. He is the first to use a greenhouse analogy.
1863: Irish scientist John Tyndall publishes a paper describing how water vapour can be a greenhouse gas.
1890s: Swedish scientist Svante Arrhenius and an American, P C Chamberlain, independently consider the problems that might be caused by CO2 building 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.
1957: US oceanographer Roger Revelle warns that humanity is conducting a "large-scale geophysical experiment" on the planet by releasing greenhouse gases. Colleague David Keeling sets up first continuous monitoring of CO2 levels in the atmosphere. Keeling soon finds a regular year-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 cause sea levels to rise by up to one metre, researchers say. The conference also reports that gases other than CO2, such as methane, ozone, CFCs and nitrous 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 CO2 emissions by the year 2005. UN sets up the Intergovernmental Panel on Climate Change (IPCC) to analyse and report on scientific findings.
1990: The first report of the IPCC finds that the planet has warmed by 0.5°C in the past century. IPCC warns that only strong measures to 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 that shields the Earth from solar energy, which helps interrupt 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 nations in 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 will disappear beneath the waves as sea levels rise - adopt a demand for 20% cuts in emissions by 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 the first full meeting of the Climate Change Convention in Berlin. Industrialised nations agree on the need to negotiate real cuts in their emissions, to be concluded by the end of 1997.
In November, the IPCC states that 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 report predicts 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 the second 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 CO2 resume their steep climb, and scientists warn that most industrialised countries will not meet Rio agreement to stabilise emissions at 1990 levels by the year 2000.
1997: Kyoto Protocol agrees 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 by trading emissions permits, establishing carbon sinks such as forests to 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 negotiations in Buenos Aires fail to resolve disputes over the Kyoto "rule book", but agree on a deadline for resolution by the end of 2000. 1998 is the hottest year in the hottest decade of the hottest century of the millennium.
2000: IPCC scientists re-assess likely future emissions and warn that, if things go badly, the world could warm by 6°C within a century. A series of major floods around the world reinforce public concerns that global warming is raising the risk of extreme weather events. But in November, crunch talks held 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 Protocol because he believes it will damage the US economy. After some hesitation, other nations agree to go ahead without him. Talks in Bonn in July and Marrakech in November finally 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's complicated rules require ratification by nations responsible for 55% of industrialised country emissions, before it can come into force. After Australia joins the US in reneging on the deal, Russia is left to make or break the treaty, but hesitates. Meanwhile, the world experiences the second hottest year on record and Antarctica's Larsen B ice sheet breaks up.
2003: Globally it is the third hottest year on record, but Europe experiences the hottest summer for at least 500 years, with an estimated 30,000 fatalities as a result. Researchers later conclude that climate 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 Russia blows hot and cold over Kyoto.
2004: A deal is struck on Kyoto. President Putin announces in May that Russia will back the Protocol. On 18 November, the Russian parliament ratifies the protocol, paving the way for it to come into force in 2005. A study links the 2003 heatwave to global warming. Hollywood blockbuster The Day After Tomorrow bases its plot on an exaggerated climate change scenario.
2005: On 16 February, the Kyoto Protocol comes into force. In December, Kyoto signatories agree to discuss emissions targets for the second compliance period beyond 2012, while countries without targets, including the US and China, agree to a "non-binding dialogue" on their future roles in curbing emissions. Europe launches its Emissions Trading Scheme, despite criticism of the idea.
2005 is the second warmest year on record. Researchers link warming to a record US hurricane season, accelerated melting of Arctic sea ice and Siberian permafrost. At a pivotal climate meeting held in Exeter, UK, scientists warn that the west Antarctic ice sheet is starting to collapse.
2006: The Stern Report, commissioned by the UK government, argues that the costs of coping with climate change will be greater than the costs of preventing it. Al Gore's climate change film An Inconvenient Truth becomes a box-office hit. Carbon dioxide emissions are found to be rising faster than in the 1990s, and new evidence bolsters the iconic "hockey stick" graph. The US Environmental Protection Agency is taken to the Supreme Court over its refusal to regulate CO2 emissions. US agencies, including NASA, are accused of trying to censor climate experts.
2007: The fourth Assessment Report of the IPCC places the blame for global warming firmly on humankind, estimates the cost of stabilising greenhouse gases at $1830 billion, and calls for governments to begin planning adaptive measures. Some of the most extreme scenarios are left out of the report, leading to accusations that it has been watered down. The synthesis report warns of "abrupt and irreversible" climate change.
Al Gore and the IPCC are awarded the Nobel Peace Prize, while a UK judge criticises An Inconvenient Truth for containing nine "factual inaccuracies". TV documentary The Great Global Warming Swindle alleges that climate science is deeply flawed – the programme is later found to have misrepresented the science and interviewed researchers complain to the British watchdog for broadcasting standards, Ofcom. In April the US Supreme Court rules that the EPA does have the authority to regulate carbon dioxide emissions.
Measurements of solar activity show that it has declined since the 1980s, debunking the claim that it is responsible for global warming. At the annual UN climate summit held in December in Bali, government representatives from around the world agree a timetable to 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 is listed on the US endangered species act, because of the risk to its habitat from climate change. Alaska threatens to sue over the decision. The World Conservation Union finds that thousands of species are at risk from climate change.
Barack Obama becomes president of the United States, promising increases in science funding, especially for climate change and energy technology. He appoints Nobel laureate winner and renewables expert Steve Chu as 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 is warming. A thin strip of ice protecting the Wilkins ice sheet from collapse breaks apart, hastening the sheet's demise – while the Arctic continues to warm much faster than expected. A major study suggests that humanity can emit no more than 1 trillion tonnes of carbon, if we are to avoid temperature rises of 2°C or more.