The Discovery of Global Warming                                                       Spencer Weart
June 2006      HOME

Timeline of Milestones

Here are gathered in chronological sequence the most important events in the history of climate change science. (For a narrative see the Introduction: summary history.) This list of milestones includes major influences external to the science itself. Following it is a list of other external influences.

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

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

Arrhenius publishes first calculation of global warming from human emissions of CO2.=>Simple models

Chamberlin produces a model for global carbon exchange including feedbacks.=>Simple models

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 reported.=>Modern temp's

Milankovitch proposes orbital changes as the cause of ice ages.=>Climate cycles

Callendar argues that CO2 greenhouse global warming is underway, reviving interest in the question.=>CO2 greenhouse

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.=>Government

Ewing and Donn offer a feedback model for quick ice age onset.=>Simple models

Phillips produces a somewhat realistic computer model of the global atmosphere.=>Models (GCMs)

Plass calculates that adding CO2 to the atmosphere will have a significant effect on the radiation balance.=>Radiation math

Launch of Soviet Sputnik satellite. Cold War concerns support 1957-58 International Geophysical Year, bringing new funding and coordination to climate studies.=>International

Revelle finds that CO2 produced by humans will not be readily absorbed by the oceans.=>CO2 greenhouse

Telescope studies show a greenhouse effect raises temperature of the atmosphere of Venus far above the boiling point of water.=>Venus & Mars

Downturn of global temperatures since the early 1940s is reported. =>Modern temp's

Keeling accurately measures CO2 in the Earth's atmosphere and detects an annual rise.=>CO2 greenhouse The level is 315 ppm.

Cuban Missile Crisis, peak of the Cold War.

Calculations suggest that feedback with water vapor could make the climate acutely sensitive to changes in CO2 level.=>Radiation math

Boulder meeting on causes of climate change, in which Lorenz and others point out the chaotic nature of climate system and the possibility of sudden shifts.=>Chaos theory

Emiliani's analysis of deep-sea cores shows the timing of ice ages was set by small orbital shifts, suggesting that the climate system is sensitive to small changes.=>Climate cycles

International Global Atmospheric Research Program established, mainly to gather data for better short-range weather prediction, but including climate.=>International

Manabe and Wetherald make a convincing calculation that doubling CO2 would raise world temperatures a couple of degrees.=>Radiation math

Studies suggest a possibility of collapse of Antarctic ice sheets, which would raise sea levels catastrophically.=>Sea rise & ice

Astronauts walk on the Moon, and people perceive the Earth as a fragile whole.=>Public opinion

Budyko and Sellers present models of catastrophic ice-albedo feedbacks.=>Simple models

Nimbus III satellite begins to provide comprehensive global atmospheric temperature measurements.=>Government

First Earth Day. Environmental movement attains strong influence, spreads concern about global degradation. =>Public opinion

Creation of U.S. National Oceanic and Atmospheric Administration, the world's leading funder of climate research.=>Government

Aerosols from human activity are shown to be increasing swiftly. Bryson claims they counteract global warming and may bring serious cooling.=>Aerosols

SMIC conference of leading scientists reports a danger of rapid and serious global change caused by humans, calls for an organized research effort.=>International

Mariner 9 spacecraft finds a great dust storm warming the atmosphere of Mars, plus indications of a radically different climate in the past.=>Venus & Mars

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.=>Rapid change

Oil embargo and price rise bring first "energy crisis".=>Government

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 talk of ice age.=>Public opinion

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

Manabe and collaborators produce complex but plausible computer models which show a temperature rise of several degrees for doubled CO2=>Models (GCMs)

Studies show that CFCs (1975)and methane and ozone (1976) can make a serious contribution to the greenhouse effect.=>Other gases

Deep-sea cores show a dominating influence from 100,000-year Milankovitch orbital changes, emphasizing the role of feedbacks.=>Climate cycles

Deforestation and other ecosystem changes are recognized as major factors in the future of the climate.=>Biosphere

Eddy shows that there were prolonged periods without sunspots in past centuries, corresponding to cold periods.=>Solar variation

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

Attempts to coordinate climate research in U.S. end with an inadequate National Climate Program Act, accompanied by rapid but temporary growth in funding.=>Government

Second oil "energy crisis." Strengthened environmental movement encourages renewable energy sources, inhibits nuclear energy growth.=>Public opinion

U.S. National Academy of Sciences report finds it highly credible that doubling CO2 will bring 1.5-4.5°C global warming.=>Models (GCMs)

World Climate Research Programme launched to coordinate international research.=>International

Election of Reagan brings backlash against environmental movement. Political conservatism is linked to skepticism about global warming.=>Government

IBM Personal Computer introduced. Advanced economies are increasingly delinked from energy.

Hansen and others show that sulfate aerosols can significantly cool the climate, raising confidence in models showing future greenhouse warming. =>Aerosols

Some scientists predict greenhouse warming “signal” should be visible by about the year 2000. =>Modern temp's

Greenland ice cores reveal drastic temperature oscillations in the space of a century in the distant past.=>Rapid change

Strong global warming since mid-1970s is reported, with 1981 the warmest year on record.=>Modern temp's

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

Villach conference declares consensus among experts that some global warming seems inevitable, calls on governments to consider international agreements to restrict emissions. =>International

Antarctic ice cores show that CO2 and temperature went up and down together through past ice ages. =>CO2

Broecker speculates that a reorganization of North Atlantic Ocean circulation can bring swift and radical climate change.=>The oceans

Montreal Protocol of the Vienna Convention imposes international restrictions on emission of ozone-destroying gases.=>International

News media coverage of global warming leaps upward following record heat and droughts plus testimony by Hansen.=>Public opinion

Toronto conference calls for strict, specific limits on greenhouse gas emissions.=>International

Ice-core and biology studies confirm living ecosystems make climate feedback by way of methane, which could accelerate global warming.=>Other gases

Intergovernmental Panel on Climate Change (IPCC) is established.=>International

Level of CO2 in the atmosphere reaches 350 ppm

After 1988 it is difficult to identify historical milestones. Not only do we lack perspective (as discussed in a separate note), but the effort was so large that progress on a given topic, even more than before, came through a variety of results spread over several groups and several years. A TENTATIVE LIST:

Fossil-fuel and other industries form Global Climate Coalition in US to lobby politicians and convince the media and public that climate science is too uncertain to justify action. =>Public opinion

First IPCC report says world has been warming and future warming seems likely. Industry lobbyists and some scientists dispute the tentative conclusions. =>International

Mt. Pinatubo explodes; Hansen predicts cooling pattern, verifying (by 1995) computer models of aerosol effects. =>Aerosols

Global warming skeptics emphasize studies indicating that a significant part of 20th-century temperature changes were due to solar influences. (The correlation would fail in the following decade.) =>Solar variation

Studies from 55 million years ago show possibility of eruption of methane from the seabed with enormous self-sustained warming. =>Rapid change

Conference in Rio de Janeiro produces UN Framework Convention on Climate Change, but US blocks calls for serious action. =>International

Study of ancient climates reveals climate sensitivity in same range as predicted independently by computer models. =>Models (GCMs)

Greenland ice cores suggest that great climate changes (at least on a regional scale) can occur in the space of a single decade. =>Rapid change

Second IPCC report detects "signature" of human-caused greenhouse effect warming, declares that serious warming is likely in the coming century. =>International

Reports of the breaking up of Antarctic ice sheets and other signs of actual current warming in polar regions begin affecting public opinion.=>Public opinion

Toyota introduces Prius in Japan, first mass-market electric hybrid car; swift progress in large wind turbines and other energy alternatives.

International conference produces Kyoto Protocol, setting targets to reduce greenhouse gas emissions if enough nations sign onto a treaty. =>International

The warmest year on record, globally averaged (1995, 1997, 2001-2004 neared the same level). Borehole data confirm extraordinary modern warming trend. =>Modern temp's

Qualms about arbitrariness in computer models diminish as teams model ice-age climate and dispense with special adjustments to reproduce current climate. =>Models (GCMs)

Criticism that satellite measurements show no warming are dismissed by National Academy Panel. =>Modern temp's

Ramanathan detects massive "brown cloud" of aerosols from South Asia. =>Aerosols

Global Climate Coalition dissolves as many corporations grapple with threat of warming, but oil lobby convinces US administration to deny problem. =>Government

Variety of studies emphasize variability and importance of biological feedbacks in carbon cycle, liable to accelerate warming.=>Biosphere

Third IPCC report states baldly that global warming, unprecedented since end of last ice age, is "very likely," with possible severe surprises. Effective end of debate among all but a few scientists.=>International

Bonn meeting, with participation of most countries but not US, develops mechanisms for working towards Kyoto targets.=>International

National Academy panel sees a "paradigm shift" in scientific recognition of the risk of abrupt climate change (decade-scale). =>Rapid change

Warming observed in ocean basins; match with computer models gives a clear signature of greenhouse effect warming. =>Models (GCMs)

Studies find surprisingly strong "global dimming," due to pollution, has retarded arrival of greenhouse warming, but dimming is now decreasing. =>Aerosols

Variety of studies increase concern that collapse of ice sheets (West Antarctica, perhaps Greenland) can raise sea levels faster than most had believed. =>Sea rise & ice

Deadly summer heat wave in Europe accelerates divergence between European and US public opinion. =>Public opinion

In controversy over temperature data covering past millenium, most conclude climate was variable (perhaps because of changes in the Sun) but not comparable to post-1980 warming. =>Modern temp's ; =>Solar variation

First major book, movie and art work featuring global warming appear. =>Public opinion

Kyoto treaty goes into effect, signed by major industrial nations except US. Japan, Western Europe, regional US entities accelerate work to retard emissions.=>International

Hurricane Katrina and other major tropical storms spur debate over impact of global warming on storm intensity. =>Sea rise & ice

Level of CO2 in the atmosphere reaches 380 ppm.

Additional External Influences 1950-1980


This is a reference list of miscellaneous significant developments that don't fit into any of the other essays: scientific-technical matters that arose altogether independently of the scientific fields covered, and are not included above in the list of major "milestones," but that did have a significant influence on climate change studies.

Before the 1950s there were practically no global warming studies as such, and all the important discoveries (the ice ages, the infrared absorption of carbon dioxide, etc.) were effectively "external."

Research on military applications of radar and infrared radiation promotes advances in radiative transfer theory and measurements =>Radiation math — Studies conducted largely for military applications give accurate values of infrared absorption by gases =>CO2 greenhouse — Nuclear physicists and chemists develop Carbon-14 analysis, useful for dating ancient climate changes =>Carbon dates, for detecting carbon from fossil fuels in the atmosphere, and for measuring the rate of ocean turnover =>CO2 greenhouse — Development of digital computers affects many fields including the calculation of radiation transfer in the atmosphere =>Radiation math, and makes it possible to model weather processes =>Models (GCMs) — Geological studies of polar wandering help provoke Ewing-Donn model of ice ages =>Simple models — Improvements in infrared instrumentation (mainly for industrial processes) allow very precise measurements of atmospheric CO2 =>CO2 greenhouse.

Analysis of automobile and airplane exhaust pollution brings recognition of complex chemical and light interactions in the atmosphere, especially involving ozone =>Other gases — Research on urban air pollution, and related industrial and military applications,improves knowledge of aerosols and atmospheric turbidity =>Aerosols — Studies of fallout from nuclear weapons tests give improved picture of circulation of aerosols in the stratosphere =>Aerosols— Studies of fallout and pesticides foster worries that human technology can bring world-wide disaster =>Public opinion — Research on small-scale phenomena in various fields of geophysics (cloud formation, soil moisture, etc.) provides information useful for setting crucial parameters in global computer models =>Models (GCMs) — Studies of rice paddies and other biological and agricultural entities show emission of large quantities of methane =>Other gases.

Neutrino experiments and new astrophysical theories suggest that the Sun could be a variable star =>Solar variation — Models of glacier flow, developed by generations of glaciologists, reveal a possibly catastrophic instability in the Antarctic ice sheet =>Sea rise & ice — Fallout from nuclear weapons tests, slowly penetrating the oceans, reveals deep circulation patterns =>The oceans — Studies of ancient reversals of the Earth's magnetic field, measured in continental rocks and the ocean floor, provide a time-marker for climate changes =>Climate cycles — Ocean geologists find huge deposits of methane-bearing ices in the world’s seabeds =>Other gases — Continued rapid improvement of digital computers and software makes possible fairly realistic models of complex systems like climate =>Models (GCMs) — Nimbus-III and other satellites, designed chiefly for weather prediction, provide global data essential for climate modelling =>Models (GCMs).

After about 1980, efforts that would be relevent to global warming were generally undertaken with an awareness of potential connections.


copyright© 2003-2005 Spencer Weart & American Institute of Physics