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Timeline (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.

1800-1870
Level of carbon dioxide gas (CO2) in the atmosphere, as later measured in ancient ice, is about 290 ppm (parts per million).

Mean global temperature (1850-1870) is about 13.6°C.

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

1824
Fourier calculates that the Earth would be far colder if it lacked an atmosphere. =>Simple models

1859
Tyndall discovers that some gases block infrared radiation. He suggests that changes in the concentration of the gases could bring climate change. =>Other gases

1896
Arrhenius publishes first calculation of global warming from human emissions of CO2. =>Simple models

1897
Chamberlin produces a model for global carbon exchange including feedbacks. =>Simple models

1870-1910
Second Industrial Revolution. Fertilizers and other chemicals, electricity, and public health further accelerate growth.

1914-1918
World War I; governments learn to mobilize and control industrial societies.

1920-1925
Opening of Texas and Persian Gulf oil fields inaugurates era of cheap energy.

1930s
Global warming trend since late 19th century reported. =>Modern temp's

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

1938
Callendar argues that CO2 greenhouse global warming is underway, reviving interest in the question. =>CO2 greenhouse

1939-1945
World War II. Military grand strategy is largely driven by a struggle to control oil fields.

1945
US Office of Naval Research begins generous funding of many fields of science, some of which happen to be useful for understanding climate change. =>Government

1956
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

1957
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

1958
Telescope studies show a greenhouse effect raises temperature of the atmosphere of Venus far above the boiling point of water. =>Venus & Mars

1960
Mitchell reports downturn of global temperatures since the early 1940s.=>Modern temp's

Keeling accurately measures CO2 in the Earth's atmosphere and detects an annual rise. =>CO2 greenhouse The level is 315 ppm. Mean global temperature (five-year average) is 13.9°C.

1962
Cuban Missile Crisis, peak of the Cold War.

1963
Calculations suggest that feedback with water vapor could make the climate acutely sensitive to changes in CO2 level. =>Radiation math

1965
Boulder, Colo. meeting on causes of climate change: Lorenz and others point out the chaotic nature of climate system and the possibility of sudden shifts. =>Chaos theory

1966
Emiliani's analysis of deep-sea cores and Broecker's analysis of ancient corals show that the timing of ice ages was set by small orbital shifts, suggesting that the climate system is sensitive to small changes. =>Climate cycles

1967
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

1968
Studies suggest a possibility of collapse of Antarctic ice sheets, which would raise sea levels catastrophically. =>Sea rise & ice

1969
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

1970
First Earth Day. Environmental movement attains strong influence, spreads concern about global degradation. =>Public opinion

Creation of US 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

1971
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

1972
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

Droughts in Africa, Ukraine, India cause world food crisis, spreading fears about climate change. =>Public opinion

1973
Oil embargo and price rise bring first "energy crisis". =>Government

1974
Serious droughts since 1972 increase concern about climate, with cooling from aerosols suspected to be as likely as warming; scientists are doubtful as journalists talk of a new ice age.=>Public opinion

1975
Warnings 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)

1976
Studies show that CFCs (1975) and also 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

1977
Scientific opinion tends to converge on global warming, not cooling, as the chief climate risk in next century. =>Public opinion

1978
Attempts to coordinate climate research in US end with an inadequate National Climate Program Act, accompanied by rapid but temporary growth in funding. =>Government

1979
Second oil "energy crisis." Strengthened environmental movement encourages renewable energy sources, inhibits nuclear energy growth. =>Public opinion

US 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

1981
Election of Reagan brings backlash against environmental movement to power. 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

1982
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

1983
Reports from US National Academy of Sciences and Environmental Protection Agency spark conflict, as greenhouse warming becomes prominent in mainstream politics. =>Government

1985
Ramanathan and collaborators announce that global warming may come twice as fast as expected, from rise of methane and other trace greenhouse gases.=>Other gases

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, pointing to powerful biological and geochemical feedbacks. =>CO2

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

1987
Montreal Protocol of the Vienna Convention imposes international restrictions on emission of ozone-destroying gases. =>International

1988
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; UK Prime Minister Thatcher is first major leader to call for action. =>International

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

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

1989
Fossil-fuel and other U.S. industries form Global Climate Coalition to tell politicians and the public that climate science is too uncertain to justify action. =>Public opinion

1990
First IPCC report says world has been warming and future warming seems likely. =>International

1991
Mt. Pinatubo explodes; Hansen predicts cooling pattern, verifying (by 1995) computer models of aerosol effects. =>Aerosols

Global warming skeptics claim that 20th-century temperature changes followed from solar influences. (The solar-climate 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

1992
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)

1993
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

1995
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 shelves and other signs of actual current warming in polar regions begin affecting public opinion. =>Public opinion

1997
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 for industrialized nations to reduce greenhouse gas emissions if enough nations sign onto a treaty (rejected by US Senate in advance). =>International

1998
"Super El Niño" causes weather disasters and warmest year on record (approximately matched by 2005, 2007 and 2010). Borehole data confirm extraordinary 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)

1999
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

2000
Global Climate Coalition dissolves as many corporations grapple with threat of warming, but oil lobby convinces US administration to deny problem. =>Public opinion

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

2001
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)

2002
Studies find surprisingly strong "global dimming," due to pollution, has retarded arrival of greenhouse warming, but dimming is now decreasing. =>Aerosols

2003
Numerous observations raise concern that collapse of ice sheets (West Antarctica, 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

2004
First major books, movie and art work featuring global warming appear. =>Public opinion

2005
Kyoto treaty goes into effect, signed by major industrial nations except US. Work to retard emissions accelerates in Japan, Western Europe, US regional governments and corporations .
=>International

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

2006
In longstanding "hockey stick" controversy, scientists conclude post-1980 global warming was unprecedented for centuries or more. =>Modern temp's The rise could not be attributed to changes in solar energy. =>Solar variation

"An Inconvenient Truth" documentary persuades many but sharpens political polarization. =>Public opinion

2007
Fourth IPCC report warns that serious effects of warming have become evident; cost of reducing emissions would be far less than the damage they will cause. =>International

Greenland and Antarctic ice sheets and Arctic Ocean sea-ice cover found to be shrinking faster than expected.=>Sea rise & ice

2009
Many experts warn that global warming is arriving at a faster and more dangerous pace than anticipated just a few years earlier. =>International

Excerpts from stolen e-mails of climate scientists fuel public skepticism.=>Public opinion

Copenhagen conference fails to negotiate binding agreements: end of hopes of avoiding dangerous future climate change. =>International

Level of CO2 in the atmosphere reaches 385 ppm.

Mean global temperature (five-year average) is 14.5°C, the warmest in hundreds, and probably thousands of years.

Heat is beating records around the country: the first five months of 2012 have been the hottest on record in the contiguous United States. And that's not including June, when 164 all-time high temperature records were tied or broken around the country, according to government records.

Related stories

In Pictures: Beating the summer heat

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That's unusual, since the most intense heat usually comes in July and August for much of the country, said Jake Crouch, a climate scientist with National Climatic Data Center. For example, only 47 all-time high records were tied or broken in June of last year.

Also, more than 40,000 daily heat records have been broken around the country so far this year, according to the National Oceanic and Atmospheric Administration. Compare that with last year —the ninth warmest on record — when only 25,000 daily records had been set by this date.

IN PICTURES: Beating the summer heat

In other words, the heat really is that bad. And behind the records is a set of weather and climate conditions that is keeping the heat locked in over the country, with little respite in sight.

Can't stand the heat

The warm summer follows an unusually warm winter, which was the hottest and driest that the western United States has ever seen since records have been kept, said Jeff Weber, a scientist with the University Corporation for Atmospheric Research in Boulder, Colo.

The heat burning up the country right now is due in part to a persistent high pressure system, also called a heat ridge or dome, which parked itself over the mountain west, and has now shifted east into the Midwest and Southeast. The system is unfortunately stuck in place, Weber said, because of a slowdown of the North Atlantic Oscillation, a climate pattern that pulls weather patterns eastward across the country.

This "blocking" of the Atlantic has caused the jet stream, which normally ferries air from west to east across the United States, to buckle and trap heat in the Midwest and Southeast, Weber told OurAmazingPlanet.

High and dry

That's not unusual in the summer, said National Weather Service meteorologist Greg Carbin. But this pattern of hot air does cover a broader area than usual, and the total amount of hot air is greater, stretching higher up in the atmosphere than normal, he said.

Dry soils, in part a product of the dry winter, exacerbate the heat. "If the soils were wetter, more energy would be absorbed by the water and the daily high temperatures wouldn't be as warm," Crouch told OurAmazingPlanet. For example, southern Georgia and Florida, drenched by Tropical Storm Debby, haven't been as hot as areas to the north in the last week or so.

Unfortunately, the heat doesn't look likely to dissipate soon, with the National Weather Service expecting warmer-than-usual temperatures to continue for the remainder of the summer across much of the country. The southwest and Rocky Mountains could be in for a reprieve soon, however, thanks to the beginning of the North American monsoon , which is predicted to start bringing moisture and cooler temperatures into the area later this week, Weber said. [Editor's note: An earlier version mischaracterized the North American monsoon.]

Climate change?

The early heat waves of summer — following higher temperatures in spring and winter — could also be part of a pattern of climate change.

"It's consistent with what we'd expect in a warming climate, but it's hard to quantify any effect climate change might have on an individual event like this heat wave," Crouch said.

While only one heat wave cannot by itself be linked to climate change, a significant increase in these types of events over time could be a hallmark of a warming planet. "An increasing frequency of heat waves —that's one aspect of climate change you can point to," Carbin said.

Over the past few years, daily record high temperatures have been outpacing daily record lows by 2-to-1 on average, according to the website Climate Central. A 2009 study found that if the climate were not warming, that ratio would be expected to be even. So far this year, there have been 40,113 high temperature records set or tied, compared with just 5,835 cold records, a ratio of about 7-to-1.

"This could be a harbinger of things to come," Weber said.

Excerpts from the Christian Science Monitor