Level of carbon dioxide gas (CO2) in the atmosphere, as later measured in ancient ice, is about 290 parts per million (ppm).

First Industrial Revolution. Coal, railroads, and land clearing speed up greenhouse gas emission, while better agriculture and sanitation speed up population growth.


French polymath Jean-Baptiste Fourier suggests the existence of an atmospheric effect keeping the Earth warmer than it would be otherwise. He also uses the analogy of a greenhouse.


Irish atmospheric scientist, John Tyndall, discovers that some gasses block infrared radiation. He publishes a paper in 1863 describing how water vapor can be a greenhouse gas, and suggests that changes in the concentration of the gases could bring about climate change.


Swedish scientist Svante Arrhenius publishes the first calculation of global warming from human emissions of CO2.


American, P.C. Chamberlain produces a model for global carbon exchange including feedbacks.


Second Industrial Revolution. Fertilizers and other chemicals, electricity, and public health further accelerate growth.


World War I; governments learn to mobilize and control industrial societies.


Opening of Texas and Persian Gulf oil fields inaugurates era of cheap energy.


Global warming trend since late 19th century is reported. Serbian astrophysicist, Milutin Milankovitch proposes orbital changes as the cause of ice ages.


British scientist, G.S. Callendar argues that CO2 greenhouse global warming is underway, reviving interest in the question.


World War II. Grand strategy is largely driven by a struggle to control oil fields.


U.S. Office of Naval Research begins generous funding of many fields of science, some of which happen to be useful for understanding climate change.


American geophysicist, Maurice Ewing (along with William Donn), offer a feedback model for a quick ice age onset. American theoretical meteorologist, Norman Phillips, produces a somewhat realistic computer model of the global atmosphere. American physicist, Gilbert Plass, calculates that adding CO2 to the atmosphere will have a significant effect on the radiation balance.


American oceanographer, Roger Revelle, warns that people are conducting a “large-scale geophysical experiment” on the planet by releasing greenhouse gases, and that CO2 produced by humans will not be readily absorbed by the oceans. His colleague, David Keeling, sets up the first continuous monitoring of CO2 levels in the atmosphere. Immediately, Keeling finds a regular year-on-year rise of CO2 levels.

The launch of Soviet Sputnik satellite heightens Cold War concerns, causing support for the 1957-1958 International Geophysical Year, bringing new funding and coordination to climate studies.


Telescope studies show a greenhouse effect raises temperature of the atmosphere of Venus, far above the boiling point of water.


Downturn of global temperatures since the early 1940s is reported. David Keeling accurately measures CO2 in the Earth’s atmosphere and detects an annual rise.


Calculations suggest that feedback with water vapor could make the climate acutely sensitive to changes in CO2 levels.


At a landmark conference on “Causes of Climate Change,” held in Boulder, Colorado, American meteorologist, Edward Lorenz (the father of chaos theory) and others point out the chaotic nature of climate systems and the possibility of sudden shifts.


Italian-American scientist, Cesare Emiliani’s analysis of deep-sea cores shows the timing of the ice ages was set by small orbital shifts, suggesting that the climate system is sensitive to small changes.


An International Global Atmospheric Research Program is established, mainly to gather data for better short-range weather predictions, but also including climate predictions.


Studies suggest a possibility of a collapse of Antarctic ice sheets, which would raise sea levels catastrophically.


Astronauts walk on the Moon, and people perceive the Earth as a fragile whole. The Nimbus III satellite begins to provide comprehensive global atmospheric temperature measurements.


A series of studies by the US Department of Energy increases concerns about future global warming. The Environmental movement attains strong influence, and the first Earth Day is established. Aerosols from human activity are shown to be increasing swiftly, which American meteorologist, Reid Bryson, proposes counteract global warming and may bring about serious cooling. The National Oceanic and Atmospheric Administration (NOAA) the world’s leader of climate research, is created.


Ice cores and other evidence show big climate shifts in the past between relatively stable modes in the space of a thousand years or so, especially around 11,000 years ago.


Serious droughts and other unusual weather since 1972 increase scientific and public concern about climate change, with cooling from aerosols suspected to be as likely as warming. Journalists began to talk of a new ice age.


Concern about environmental effects of airplanes leads to investigations of trace gases in the stratosphere and discovery of danger to the ozone layer.


Studies show that CFCs, methane, and ozone can make a serious contribution to the greenhouse effect. Deep-sea cores show a dominating influence from 100,000-year Milankovitch orbital changes, emphasizing the role of feedbacks. Deforestation and other ecosystem changes are recognized as major factors in the future of the climate.


Scientific opinion tends to converge on global warming, not cooling, as the chief climate risk in the next century.


The first World Climate Conference adopts climate change as major issue and calls on governments “to foresee and prevent potential man-made changes in climate.” A strengthened environmental movement encourages renewable energy sources, and inhibits nuclear energy growth. A US National Academy of Sciences report find it highly credible that doubling CO2 will bring 1.5 to 4.5 degrees centigrade global warming.


The election of Ronald Reagan brings a backlash against the environmental movement. Political conservatism is linked to skepticism about global warming.


Reports from the US National Academy of Sciences and Environmental Protection Agency spark conflict, as greenhouse warming becomes prominent in mainstream politics.


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 a meter, researchers say. Conference also reports that gases other than CO2, such as methane, ozone, CFCs and nitrous oxide, will also contribute to warming.


Warmest year on record thus far. The 1980s turn out to be the warmest decade, 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. The Montreal Protocol of the Vienna Convention imposes international restrictions on emission of ozone-destroying gases.


Global warming attracts worldwide headlines after Dr. James Hansen of NASA Goddard Institute for Space Studies lab tells a Congressional hearing “global warming is at hand.” And blames a major US drought – which fueled massive wildfires in Yellowstone Park – on its influence. Meeting of climate scientists in Toronto subsequently calls for 20 per cent cuts in global CO2 emissions by the year 2005. UN sets up the Intergovernmental Panel on Climate Change (IPCC) to analyze and report on scientific findings.

US Congresswoman, Claudine Schneider (R-RI), authors the first significant piece of legislation aimed at reducing greenhouse gas emissions, the Global Warming Prevention Act.


The first IPCC report finds that the plant has warmed by 0.5 degrees C in the past century. IPCC warns that only strong measures to halt rising greenhouse gas emissions will prevent serious global warming. Provides scientific clout for UN negotiations for a climate convention. Negotiations begin after the UN General Assembly in December. Industry lobbyists and some scientists dispute the tentative conclusions.


Mt. Pinatubo explodes in the Philippines, throwing debris into the stratosphere that shields the Earth from solar energy, which help 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. Global warming skeptics emphasize studies indicating that a significant part of 20th-century temperature changes were due to solar influences.


The Framework Convention on Climate Change, signed by 154 nations in Rio, agrees to prevent “dangerous” warming from greenhouse gases and sets initial target of reducing emissions from industrialized countries to 1990 levels by the year 2000. President George Bush signs on behalf of the United States.

More than 4,000 scientists from 106 countries, including 72 Nobel Prize winners, signed the Heidelberg Appeal, calling for a rational scientific approach to environmental problems.


The hottest year yet. The Berlin Mandate is agreed by signatories at the first full meeting of the Climate Change Convention in Berlin. Industrialized nations agree on the need to negotiate real cuts in their emissions, to be concluded by the end of 1997. The IPCC agrees 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.”


At the second meeting of the Climate Change Convention, the US and President Bill Clinton’s administration agree for the first time to legally binding emissions targets and sides with the IPCC against influential “skeptical” scientists. After a four year pause, global emissions of CO2 continue their steep climb, and scientists warn that most industrialized countries will not meet Rio agreement to stabilize emissions at 1990 levels by the year 2000.


International conference produces Kyoto Protocol, which suggests legally binding emissions cuts for industrialized nations, averaging 5.5 per cent, to be met by 2010. The US government says it will not ratify the agreement unless it sees evidence of “meaningful participation” in reducing emissions from developing countries.


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.


Newly elected US President, George W. Bush, renounces the Kyoto Protocol because he questions the science and he believes it will damage the US economy.


The United States sends its “U.S. Climate Action Report 2002,” to the UN. The report “strongly concludes that no matter what is done to cut emissions in the future, nothing can be done about the environmental consequences of several decades’ worth of carbon dioxide and other heat-trapping gases already in the atmosphere.” It further states that “some of the goods and services lost through the disappearance or fragmentation of natural ecosystems are likely to be costly or impossible to replace.”


Variety of studies increase concern that collapse of ice sheets can raise sea levels faster than most had believed. A deadly summer heat wave in Europe accelerates divergence between European and US public opinion.


In controversy over temperature data covering past millennium, most conclude climate variations were substantial, but not comparable to post-1980 warming.


Kyoto treaty goes into effect, signed by major industrial nations except for the US, Japan, and Western Europe. Hurricane Katrina and other major tropical storms spur debate over impact of global warming on storm intensity.


A group describing itself as "sixty scientists" signed an Open Letter to Canadian Prime Minister Stephen Harper to ask that he revisit the science of global warming and "Open Kyoto to debate". As with the earlier statements, critics pointed out that many of the signatories were non-scientists or lacked relevant scientific backgrounds.


The first major global assessment of climate change science in six years has concluded that changes in the atmosphere, the oceans and glaciers and ice caps show unequivocally that the world is warming. The Intergovernmental Panel on Climate Change (IPCC) concludes that major advances in climate modeling and the collection and analysis of data now give scientists “very high confidence” (at least a 9 out of 10 chance of being correct) in their understanding of how human activities are causing the world to warm.