Chronology (Global Warming)

4.5 billion years ago

The Earth, newly formed, had the hottest climate in the planet’s long history. Temperatures were hot enough to liquefy rock. Radioactive elements in Earth’s core generated heat and pressure as they decayed, pushing molten rock toward Earth’s surface. Volcanoes also brought molten rock to the surface, liberating heat. Volcanoes spewed carbon dioxide into the atmosphere, causing the Greenhouse Effect.

3.8 billion years ago

As the mass of radioactive elements in Earth’s core diminished, the climate cooled and the first rock formed. The cooling of the atmosphere liquefied water vapor, which fell to Earth as rain.

3.5 billion years ago to 3 billion years ago

The origin of life enhanced the cooling of the climate, for among the first life were single-celled photosyn-thetic algae. Like plants, these algae consumed carbon dioxide and exuded oxygen. The reduction of carbon dioxide in the atmosphere weakened the Greenhouse Effect. With the reduction in carbon dioxide, temperatures dropped below freezing, causing the planet’s first ice age 3 billion years ago.

2.9 billion years ago

The retreat of the glaciers inaugurated a long period of warm climate. The sun, burning steadily brighter, bathed Earth in its heat. Warm inland seas covered Earth, moderating the climate. Ocean currents circled the globe, spreading warm water from the equator to the poles.

800 million years ago to 550 million years ago

Glaciers covered the oceans as well as the land, killing photosynthetic algae that lived in the ocean. With algae in small numbers they were able to remove only a fraction of carbon dioxide from the atmosphere. With no check on its accumulation, carbon dioxide increased in the atmosphere, causing the Greenhouse Effect. The Greenhouse Effect ended the Late Pro-terozoic Ice Age roughly 550 million years ago, inaugurating a new warm period.

350 million years ago to 280 million years ago

The lush plant growth of the Carboniferous Era confirmed that the climate was warm and that carbon dioxide, essential for plant growth, was abundant.

230 million years ago

The continents gathered into a single landmass called Pangea. Because it was near the equator, Pangea’s climate was tropical.

135 million years ago to 65 million years ago

Temperatures soared 20 degrees Fahrenheit warmer than today’s temperatures during the Cretaceous Era.

Forests covered Antarctica. Ocean currents again carried warm water to the poles.

65 million years ago

An enormous meteor impacted Earth, ejecting a gigantic cloud of debris and dust. It ignited widespread fires, which pumped ash into the atmosphere. The debris, dust, and ash blocked out much of the sun’s light, chilling the climate. So severe was the reversal in climate that the dinosaurs and a large number of marine species, unable to cope with the new conditions, perished.

55 million years ago to 35 million years ago

Temperatures declined 20 degrees F (11 degrees C). Glaciers formed on Antarctica.

130,000 years ago

The climate was again warmer than it is today. The water from melting glaciers flowed to the oceans, raising the sea level 60 ft. (18 m.) higher than it is today.

100,000 years ago

The climate cooled yet again and glaciers once more spread across the continents, plunging Earth into its most recent ice age.

16,000 to 13,000 years ago

The glaciers were in retreat, temperatures rose nearly 15 degrees Fahrenheit.

12,900 and 11,500 years ago

Temperatures during the Younger Dryas fell 50 degrees Fahrenheit in only a decade

7,000 years ago

Temperatures peaked at 2-3 degrees F (1-1.5 degrees C) above current temperatures. The climate remained warm and wet for another 3,000 years.

1,000 to 1,300 c.E.

The Medieval Warm Period rewarded peasants with bountiful crops. With food in surplus, human population increased.

1400 to 1840

The Little Ice Age covered the globe with record cold, large glaciers, and snow. This massive climate change triggered disease, famine, and death. Today, many scientists around the world believe that global warming caused by the Greenhouse Effect will be the fastest warming of the Earth since the termination of the Little Ice Age.


French mathematician and physicist Jean Baptiste Joseph Fourier established that a buildup of carbon dioxide in Earth’s atmosphere warms the climate.


Irish scientist John Tyndall discovered that some gases block infrared radiation. He suggested that changes in the concentration of the gases could bring climate change.


Tyndall announced that water vapor is a greenhouse gas.


British scientist James Croll established that ice and snow reflect sunlight into space and cool the Earth.


Swedish scientist and Nobel laureate Svente Arrhenius coined the phrase Greenhouse Effect and predicted that the Earth’s climate is slowly warming. Arrhenius published the first calculation of global warming from human-induced emissions of carbon dioxide.


British scientist Thomas C. Chamberlin established the link between ice ages and low concentrations of carbon dioxide and between warm climates and high concentrations of carbon dioxide.

1920 to 1925

The opening of Texas and Persian Gulf oil fields inaugurated an era of cheap energy. The burning of petroleum releases greenhouse gases into the atmosphere, warming the climate.


German climatologist and geologist Alfred Wegener posited that the continents move slowly across Earth. When they are near the equator their climate is warm, while near the poles their climate is cold.


Serbian geophysicist Milutin Milankovitch proposed that changes in the eccentricity of Earth’s orbit cause climate change, including ice ages.


Meteorologist W.J. Humphreys elaborated the conditions for a return to an ice age. He believed that an increase in debris in the atmosphere and the reflection of sunlight by ice and snow might return Earth to an ice age.

1933 to 1935

The drought of the 1930s created dust storms on the Plains. The worst dust storm of the Dust Bowl gripped the Plains on what later becomes known as Black Sunday. President Franklin Roosevelt established the Soil Erosion Service in response to the devastation of the Dust Bowl and as a part of his New Deal programs to create jobs. The Soil Erosion Service was the predecessor of the Soil Conservation Service established in 1935, which is known today as the Natural Resources Conservation Service (NCRS).


Royal Meteorological Society president George Simpson posited that an increase in solar radiation might cause an ice age. By warming the poles more than high altitudes, the increase in solar radiation would intensify the circulation of the atmosphere, carrying moisture to high latitudes, where it would fall as snow. If enough snow accumulated, a new ice age would ensue.


Amateur scientist G.S. Callendar recorded an increase in temperatures in the Artic and posited the Greenhouse Effect as the cause.


Simpson announced that the atmosphere seems to keep the climate nearly constant by regulating the amount of clouds. The more clouds, the lower the temperature, and the fewer clouds, the warmer the temperature.


Many scientists dismissed Callendar’s claims. However, in response to his theory scientists began to develop new ways to measure the history of and current conditions of Earth’s climate.


The U.S. Office of Naval Research began generous funding of many fields of science, some of them useful for understanding climate change.


American scientist Charles F. Brooks announced that Artic ice might be melting and that, once started, the melting might shrink the ice to a vestige of its former size and raise sea levels.


The development of new technology led to an increased awareness of global warming and the Greenhouse Effect. Researchers began to show that the level of carbon dioxide in the atmosphere was rising each year and people became concerned about pollution.


American scientists Maurice Ewing and William Donn posited that the last ice age had rapidly descended on Earth when the North Pole wandered into the Arctic Ocean, triggering the accumulation of snow and ice in this region. American scientist Norman Phillips produces a somewhat realistic computer model of the global atmosphere. Canadian physicist Gilbert Plass calculated that adding carbon dioxide to the atmosphere would affect the radiation balance.


Launch of Soviet Sputnik satellite. Cold War concerns support the 1957-58 International Geophysical Year, bringing new funding and coordination to climate studies. U.S. oceanographer Roger Revelle warned that humanity is conducting a "large-scale geophysical experiment" on the planet by releasing greenhouse gases.


Astronomers identified the Greenhouse Effect on Venus, where temperatures are far above the boiling point of water.


A report found that global temperatures had declined since the early 1940s. American scientist Charles David Keeling set up the first continuous monitoring of carbon dioxide levels in the atmosphere. Keeling soon finds a regular rise in temperatures.


Soviet meteorologist Mikhail Budyko warned that the burning of fossil fuels, and the attendant accumulation of greenhouse gases in the atmosphere, would warm the planet.


Fritz Moller calculated that a doubling of carbon dioxide in the atmosphere might increase temperatures 50 degrees Fahrenheit.


Climatologists gather in Boulder, Colorado, to discuss climate change. Edward Lorenz and others point out the chaotic nature of the climate system and the possibility of sudden shifts.


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


The International Global Atmospheric Research Program was established, mainly to gather data for better short-range weather prediction. Computer modelers Syukuro Manabe and Richard Wetherald predicted that an increase in the number of clouds might hold heat in the atmosphere and so increase temperatures.


Mikhail Budyko derived two mathematical models. One predicted an increase in temperatures due to the Greenhouse Effect. The other predicted the return of the ice age. Budyko favored the first model. Other models were also contradictory. Studies suggested that the Antarctic ice sheets might collapse, raising sea levels catastrophically.


American climatologist William Sellers predicted that a 2 percent decrease in solar radiation, whether from a fluctuation in solar output or the result of debris in the air, might plunge Earth into a new ice age. Like Budyko, Sellers feared that the burning of fossil fuels might warm Earth. Nimbus III satellite begins to provide comprehensive global atmospheric temperature measurements.


The First Earth Day. The environmental movement attains strong influence, spreading concern about global degradation. The creation of the U.S. National Oceanic and Atmospheric Administration was the world’s leading funder of climate research. Aerosols from human activity were increasing in the atmosphere. American scientist Reid Bryson claimed they counteracted global warming and may actually cool the Earth.


The Study of Man’s Impact on Climate (SMIC), a conference of leading scientists, reported a danger of rapid and serious global change caused by humans and called for an organized research effort. The American Mariner 9 spacecraft found a great dust storm warming the atmosphere of Mars along with indications of a radically different climate in the planet’s past.


Budyko predicted that a 50 percent increase in greenhouse gases in the atmosphere might raise temperatures enough to melt all the ice on Earth, whereas a 50 percent reduction might plunge Earth into an ice age. Budyko favored the first scenario and predicted that temperatures might rise enough to melt all the ice by 2050. Ice cores and other evidence showed that the climate changed in the past in the space of 1,000 years or so, especially around 11,000 years ago.

1972 to 1974

Serious droughts and other unusual weather since 1972 increased scientific and public concern about climate change, with cooling from aerosols suspected to be as likely as warming. Journalists wrote about ice ages.


Concern about the environmental effects of airplanes led to investigations of trace gases in the stratosphere and the discovery of danger to the ozone layer. Manabe and collaborators produced complex but plausible, computer models, which predicted an increase of several degrees Fahrenheit for a doubling of carbon dioxide.

1975 to 1976

Studies showed that chlorofluorocarbons (CFCs) (1975) and also methane and ozone (1976) contribute to the Greenhouse Effect. Deep-sea cores show a dominating influence from 100,000-years ago. Mila-nkovitch’s prediction of orbital changes emphasized the role of feedbacks. Deforestation and other ecosystem changes were recognized as major factors in the future of the climate. American meteorologist Amos Eddy showed that the absence of sunspots in past centuries corresponded with cold periods.


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


Attempts to coordinate climate research in United States ended with an inadequate National Climate Program Act, accompanied by rapid, but temporary, growth in funding. American scientist James Hansen predicted that the accumulation of aerosol particles in the atmosphere might reflect sunlight back into space and so reduce temperatures.


The second oil energy crisis. A strengthened environmental movement encouraged the development of renewable energy sources and the reduction of technologies that burn fossil fuels. The U.S. National Academy of Sciences estimated that a doubling of carbon dioxide might increase temperatures 35 to 40 degrees Fahrenheit. The World Climate Research Program was launched to coordinate international research on climate change.


The election of President Ronald Reagan caused a backlash against the environmental movement. Political conservatism is linked to skepticism about global warming. Some scientists predicted greenhouse warming should be measurable by about the year 2000.


Greenland ice cores revealed temperature oscillations over a single century in the distant past. Strong global warming since the mid-1970s was reported, with 1981 the warmest year on record.


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


Theories about global warming and the Greenhouse Effect became more prevalent, gaining attention from the mass media. However, many people believe the threat is not imminent and some doubt that global climate change is a danger.


The Center for Atmospheric Science Director Veer-abhadran Ramanathan and collaborators announced that methane and other trace gases together could bring as much global warming as carbon dioxide itself. The Villach conference in Indonesia declared consensus among experts that some global warming seems inevitable and called on governments to consider international agreements to restrict emissions of greenhouse gases. Antarctic ice cores show that carbon dioxide and temperature went up and down together through past ice ages, pointing to powerful biological and geochemical feedbacks. American scientist Wallace Broecker speculated that a reorganization of North Atlantic Ocean circulation could bring swift and radical climate change.


This was the warmest year since humans began to keep records. The 1980s were 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. The Montreal Protocol of the Vienna Convention imposed international restrictions on the emission of ozone-destroying gases.


Global warming attracts worldwide headlines after scientists at Congressional hearings in Washington, D.C., blamed the U.S. drought on its influence. A meeting of climate scientists in Toronto subsequently called for 20 percent cuts in global carbon dioxide emissions by 2005. The United Nations set up the Intergovernmental Panel on Climate Change (IPCC) to analyze and report on scientific findings. News media coverage of global warming leapt upward following record heat and droughts. The Toronto conference called for strict, specific limits on greenhouse gas emissions. British Prime Minister Margaret Thatcher is the first major leader to call for action. Ice-core and biology studies confirmed that living ecosystems give climate feedback by way of methane, which could accelerate global warming. The level of carbon dioxide in the atmosphere reached 350 parts per million.


Fossil-fuel suppliers and other industries formed the Global Climate Coalition in the United States to lobby politicians and convince the media and public that climate science is too uncertain to justify action.


American meteorologist Richard Lindzen predicted that an increase in carbon dioxide in the atmosphere might not cause a concomitant increase in water vapor. Consequently, the Greenhouse Effect might be less severe than some were forecasting. The first IPCC report stated that the world has been warming and continued warming seems likely in the future. Industry lobbyists and some scientists disputed the tentative conclusions.


Mount Pinatubo erupted. Hansen predicted that the eruption would cool Earth, verifying (by 1995) computer models of aerosol effects. Global warming skeptics emphasized research indicating that a significant part of 20th-century temperature change was due to solar influences. Studies from 55 million years ago show the possibility of the eruption of methane from the seabed causing enormous warming.


A conference in Rio de Janeiro produced the United Nations Framework Convention on Climate Change, but the United States blocked calls for serious action. The study of ancient climates revealed climate sensitivity in the same range as predicted by computer models.


Greenland ice cores suggested that great climate changes (at least on a regional scale) could occur in the timespan of a single decade.


The second IPCC report detected the "signature" of human-caused Greenhouse Effect warming, declaring that serious warming is likely in the coming century. Reports of the breaking up of the Antarctic ice sheets and other signs of current warming in polar regions began to affect public opinion.


Japanese automobile manufacturer Toyota introduces the Prius in Japan, the first mass-marketed electric hybrid car. Engineers progressed in the design of large wind turbines and other energy alternatives. An international conference in Japan produced the Kyoto Protocol, setting targets to reduce greenhouse gas emissions—if enough nations would approve and sign the treaty.


The warmest year on record globally averaged (1995, 1997, and 2001-2006 were near the same level). Borehole data confirmed extraordinary warming trend. Qualms about arbitrariness in computer models diminish as teams model ice-age climate and dispense with special adjustments to reproduce current climate.


A National Academy Panel dismissed criticism that satellite measurements showed no warming. V. Ramanathan detected massive "brown cloud" of aerosols from South Asia.


The Global Climate Coalition dissolved as many corporations grappled with the threat of warming, but the oil lobby convinced the U.S. administration to deny the problem. Various studies emphasized variability and the importance of biological feedbacks in the carbon cycle that are liable to accelerate warming.


The Third IPCC report stated that global warming, unprecedented since the end of last ice age, is "very likely," with possible severe surprises. The National Academy panel marked a "paradigm shift" in scientific recognition of the risk of abrupt climate change (decade-scale). Warming is observed in ocean basins. These observations match computer models, giving a clear signature of Greenhouse Effect.


Studies found surprisingly strong "global dimming," due to pollution. This factor had retarded greenhouse warming, but dimming is now decreasing.


Numerous observations raised concern that the collapse of ice sheets (West Antarctica, Greenland) might raise sea levels faster than most had believed. A deadly summer heat wave in Europe deepens divergence between European and U.S. public opinion.


In a controversy over temperature data covering the past millennium, most scientists concluded that climate variations were substantial, but not comparable to post-1980 warming.


The Kyoto Treaty, signed, by all major industrial nations except the United States, took effect. Work to retard greenhouse emissions accelerated in Japan, Western Europe, U.S. regional governments, and corporations. Hurricane Katrina and other major tropical storms spurred debate over the impact of global warming on storm intensity.


An Inconvenient Truth premiered at the 2006 Sundance Film Festival and opened in New York and Los Angeles on May 24, 2006, earning $49 million.


The fourth IPCC report warned that serious effects of warming have become evident. The cost of reducing emissions would be far less than the damage they will cause. Al Gore shared the Nobel Peace Prize for his efforts to spread knowledge about global warming. The level of carbon dioxide in the atmosphere reaches 382 parts per million.

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