History of climate change

This graph, based on the comparison of atmospheric samples contained in ice cores and more recent direct measurements, provides evidence that atmospheric CO2 has increased since the Industrial Revolution. (Credit: Luthi, D., et al.. 2008; Etheridge, D.M., et al. 2010; Vostok ice core data/J.R. Petit et al.; NOAA Mauna Loa CO2 record.)

Estimated world population: 545–579 million

Estimated size of world economy: $77 billion

Estimated atmospheric carbon dioxide: 274 ppm*

*This abbreviation stands for parts per million. It is the ratio of the number of CO2 molecules to the total number of molecules of dry air. That is, 274 ppm means 274 molecules of CO2 per million molecules of dry air, or 0.0274 percent.

CARBON DIOXIDE DISCOVERED

Johann Baptista van Helmolt, Flemish alchemist, determined that air is a mixture of gases. He studied the gas given off when wood and other fuels were burned, which is carbon dioxide, determining that it is not healthy to breathe. In an experiment, he burned coal to see how much carbon dioxide it added to the air.

Estimated world population: 470–545 million

Estimated size of world economy: $82 billion

Estimated atmospheric carbon dioxide: 277 ppm

Estimated world population: 600–679 million

Estimated size of world economy: $100 billion

Estimated atmospheric carbon dioxide: 277 ppm

Estimated world population: 629–961 million

Estimated size of world economy: $135 billion

Estimated atmospheric carbon dioxide: 277 ppm

THE FIRST CARBON DIOXIDE DETECTOR

Joseph Black, a medical student in Edinburgh, figured out that limewater can be used as a carbon dioxide (CO2) detector. He observed that the normally clear liquid turned milky when exposed to “fixed air,” which is what he called CO2. He started measuring the gas everywhere with his limewater, and found that it was released from mineral water, fermenting yeast, burning coal and oil, cremating corpses, and human exhalation. The limewater instrument was later improved by Lord Cavendish, and became known as the Cavendish Apparatus.

INDUSTRIAL REVOLUTION BEGINS

Since the start of the Industrial Revolution, the way people live and work has changed dramatically as manufacturing expanded. Over time, the amount of fossil fuels burned increased, which has increased the amount of carbon dioxide (CO2) in the atmosphere . Before the Industrial Revolution, there was approximately 280 parts per million (ppm) of CO2 in the air. Today, that amount is over 400 ppm.

Estimated world population: 813 million–1.1 billion

Estimated size of world economy: $175 billion

Estimated atmospheric carbon dioxide: 284 ppm

DESCRIBING EARTH’S ATMOSPHERE AS A GREENHOUSE

Jean-Baptiste-Joseph Fourier, a mathematician working for Napoleon, was the first to describe how Earth’s atmosphere retains warmth on what would otherwise be a very cold planet.. To help explain the concept, he compared the atmosphere to the glass walls of a greenhouse.

Estimated world population: 1.1–1.4 billion

Estimated size of world economy: $360 billion

Estimated atmospheric carbon dioxide: 286 ppm

DISCOVERING GASES THAT TRAP HEAT

Eunice Foote, American scientist, discovered that carbon dioxide and water vapor cause air to warm in sunlight. In 1856, she presented her findings at the meeting of the American Association for the Advancement of Science (AAAS). “A paper was read before the late meeting of the Scientific Association, by Prof. Henry for Mrs. Eunice Foot, detailing her experiments to determine the effects of the sun’s rays on different gases,” noted an 1856 article in Scientific American.

TESTING THE HEAT-TRAPPING ABILITY OF GASES

John Tyndall, British physicist, tested the gases in the atmosphere to find out which are responsible for the greenhouse effect. He found that nitrogen and oxygen, which make up almost all of the atmosphere, have no ability to trap heat, but that three gases present in smaller quantities do: carbon dioxide, ozone, and water vapor. Tyndall speculated that if the amounts of these gases dropped, it would chill the Earth.

CLIMATE RECORDED IN DUST

Self-taught geologist John Hardcastle realized that large deposits of wind-blown dust (known as loess) in New Zealand record changes in climate from Ice Ages to warm periods in between.

“This growing dust heap played the part of an observant bystander, taking notes of certain climatic phenomena as they successively arose.”

CONNECTING COAL, CARBON DIOXIDE, AND CLIMATE

Swedish chemist Svante Arrhenius recognized that burning coal could increase carbon dioxide and warm the climate. He estimated how much carbon dioxide the ocean could absorb. In an 1896 lecture, Arrhenius noted that it was not yet possible to calculate how fast temperature was rising. He also speculated that warming would be beneficial as people in the future "might live under a milder sky and in less barren surroundings."

Estimated world population: 1.5–1.8 billion

Estimated size of world economy: $1.1 trillion

Estimated atmospheric carbon dioxide: 300 ppm

INCREASING CARBON DIOXIDE AND INCREASING TEMPERATURES

British coal engineer George Callendar compiled all carbon dioxide measurements made over the previous 100 years and found that the amount of CO2 was increasing. He also found that temperatures were rising. His conclusion was that this was a good thing, that “the return of the deadly glaciers should be delayed indefinitely.”

Estimated world population: 2.4–2.6 billion

Estimated size of world economy: $4.1 trillion

Estimated atmospheric carbon dioxide: 311 ppm

DWINDLING ARCTIC SEA ICE

Measurements since the 1950s indicate that the amount of sea ice in the Arctic has been declining. The Arctic is projected to have no summer ice cover by the middle of this century.

AIR POLLUTION DAMPENS THE AMOUNT OF WARMING

Aerosols, emitted into the atmosphere from smokestacks and tailpipes, caused a slight cooling of climate, which fueled speculation that we could enter an Ice Age. As countries passed clean air legislation, aerosol pollution decreased and climate warming continued.

OUR UNINTENDED EXPERIMENT

Roger Revelle, U.S. oceanographer, and Hans Suess, Austrian-born U.S. chemist, realizing that carbon dioxide from industrial sources must be building up in the atmosphere, wrote in 1957: “Thus human beings are now carrying out a large scale geophysical experiment of a kind that could not have happened in the past nor be reproduced in the future.”

CLIMATE SCIENCE ON TELEVISION

The Bell Telephone Science Hour addressed how our actions could be changing Earth’s climate. “Even now, [we] may be unwittingly changing the world's climate through the waste products of [our] civilization,” said the narrator. “Due to our release from factories and automobiles every year of more than six billion tons of carbon dioxide, which helps the air absorb heat from the Sun, our atmosphere seems to be getting warmer.”

DAILY MEASUREMENTS OF CARBON DIOXIDE

Charles Keeling started making daily measurements of the amount of carbon dioxide in the air atop Mauna Loa in Hawaii. That first March day, he found 313 parts per million (ppm) of carbon dioxide in the air. The measurements, which are still made each day, reached 400 ppm on May 9, 2013, and continue to climb.

SIMPLE MODELS TO STUDY THE ATMOSPHERE

Syukuro Manabe and Richard Wetherald developed a basic model of the atmosphere at NOAA. With the model, they found that more carbon dioxide in the atmosphere causes higher temperatures at Earth's surface. This simple model was the first step toward development of complex Earth system models. (Read their 1967 paper.)

"Greenhouse gases are the second most important factor for climate, after the Sun." - Syukuro Manabe

MODELING THE WHOLE ATMOSPHERE

At the National Center for Atmospheric Research, scientists Akira Kasahara and Warren Washington developed a model of the whole atmosphere called a general circulation model. At first, they ran the model on a CDC 3600, a computer that filled a room yet only had a single processor.

“We pretty much beat the thing up because we were running a general circulation model on it 24 hours a day, seven days a week,” said Washington. “They didn’t anticipate for people to use computers in that way.”

ICE CORE UNCOVERS 8,200 YEARS OF CLIMATE

At Camp Century, Greenland, an ice core was extracted that showed 8,200 years of annual snow accumulation as thin layers in the ice. The thin layers of ice allowed scientists to reconstruct ancient climate using an ice core for the first time.

CLIMATE HISTORY PRESERVED ON THE OCEAN FLOOR

In 1966, a shipbuilding company began making a ship with a drill rig on top for the Deep Sea Drilling Project, a project based at the Scripps Institute of Oceanography in San Diego, California. The drill rig would allow scientists to collect cores from the ocean floor around the world that contain layers of sediments – a record of ancient changes in climate over millions of years. Today the Integrated Ocean Drilling Program continues to collect these deepsea records.

BETTER MODELS AND FASTER COMPUTERS

More powerful supercomputers like the Cray 1A allowed researchers to develop more complex models that included the dynamics of both the atmosphere and ocean. Their results confirmed those from earlier models: climate is warming because of the greenhouse gases added to the atmosphere.

DRILLING 150,000 YEARS DEEPER INTO THE ICE

Ice cores extracted from Antarctic ice in 1985 showed carbon dioxide and temperature had gone up and down together in wide swings over the past 150,000 years, the same relationship that computer models suggested.

CLIMATE IN CONGRESS

NASA climate scientist James Hansen testified before the Senate Energy and Natural Resources Committee stating that climate was warming, greenhouse gases are responsible for the warming, and we are responsible for the growth in these gases.

INTERGOVERNMENTAL PANEL ON CLIMATE CHANGE (IPCC) FORMED

The IPCC was formed by the World Meteorological Organization and the United Nations to review the latest climate science every few years and help governments around the world understand what we know about climate change, its impacts, and efforts to adapt and mitigate.

CLIMATE SYSTEM MODELS

New models were developed to include how the ocean, land, sea ice, and atmosphere interact to affect the climate. At the end of the decade, the National Center for Atmospheric Research ran a new model, the Community Climate System Model (CCSM), on its latest supercomputer to learn more about interactions in Earth’s climate system.

REGIONAL CLIMATE MODELING

Robert Dickinson led a team to create a regional climate model for the western United States in 1989 and, in 1990, Filippo Giorgi simulated regional climate using a model nested in a general circulation model (GCM). Regional climate modeling has allowed predictions of how global climate change impacts local areas.

FIRST CLIMATE ASSESSMENT REPORT BY THE IPCC

Published in 1990, the IPCC’s First Assessment Report stated that it was certain that “human activities are substantially increasing the atmospheric concentrations of greenhouse gases.”According to the report, greenhouse gas increases had caused temperature to increase by 0.3° to 0.6° Celsius (0.5 - 1.1° Fahrenheit) over the past century and would cause global average temperature to warm about 1°C (1.8°F) by 2025 and 3°C (5.4°F) by 2100. Projections for regional temperature and precipitation changes were highly uncertain.

AN INCREASINGLY ACIDIC OCEAN

U.S. scientists Stephen V. Smith and R.W. Buddemeier pointed out that more carbon dioxide (CO2) in the ocean could be a problem for coral reefs. Later experiments confirmed their hypothesis that CO2 makes seawater slightly acidic, which makes it difficult for corals and other animals to build reefs. Today at NCAR, scientist Joanie Kleypas builds on their work, researching the impacts of acidic oceans on marine life.

EVIDENCE SUGGESTS HUMAN INFLUENCE ON CLIMATE

The Second Assessment Report of the IPCC provided key information that led to the development of the Kyoto Protocol in 1997. “Considerable progress has been made in the understanding of climate change science since 1990,” wrote the authors. Acknowledging that global climate had changed over the past century, the authors noted that regional climate change was also evident and that sea level was rising.

“The balance of evidence suggests a discernible human influence on global climate.”

Estimated world population: 6.07 billion

Estimated size of world economy: $41 trillion

Estimated atmospheric CO2 in 2000: 369 ppm

NEW AND STRONGER EVIDENCE THAT WE ARE CAUSING CLIMATE CHANGE

According to the IPCC Third Assessment Report, “there is new and stronger evidence that most of the warming observed over the last 50 years is attributable to human activities.” Climate models projected that, between 1990 and 2100, Earth would warm by 1.4 to 5.8°C (2.5 to 10.4°F), depending on how much greenhouse gas we emit. “The projected rate of warming is very likely to be without precedent during at least the last 10,000 years,” noted the authors.

HEAT WAVE LINKED TO CLIMATE CHANGE

Researchers determined that climate change played a large role in the 2003 heatwave in Europe, which resulted in more than 30,000 deaths.

FINDING REALLY OLD ICE AND ITS CLIMATE HISTORY

A deep ice core from East Antarctica helped us understand how climate has changed over the past 650,000 years. Studying ancient air bubbles in the ice, scientists have learned details about the ancient atmosphere, including that levels of carbon dioxide are unusually high today compared to past interglacial periods.

ECONOMIC IMPACTS OF CLIMATE CHANGE

The Stern Review described the economic impacts of climate change, finding that mitigating (reducing the amount of greenhouse gas emissions) and adapting (making changes to the way we live) would be much less expensive than the cost of trying to recover from the disastrous impacts of climate change in the future.

STUDYING IMPACTS IN THE POLAR REGIONS

During International Polar Year, which was actually two years’ long (2007-2008), scientists documented numerous impacts of climate change on the polar regions, which are warming more rapidly than other areas of Earth. Impacts included melting ice, thawing permafrost, and changes in ecosystems. They found that changes were especially pronounced in the Arctic.

CLIMATE CHANGE INDISPUTABLE

The IPCC Fourth Assessment Report noted that human-caused greenhouse gas emissions had increased 70% between 1970 and 2004 and the effects of climate change were becoming apparent. “Warming of the climate system is unequivocal,” wrote the authors of the 2007 report, “as is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice and rising global average sea level.”

“Anthropogenic [human-caused] warming could lead to some impacts that are abrupt or irreversible,” they warned. “More extensive adaptation than is currently occurring is required to reduce vulnerability to climate change.”

EARTH SYSTEM MODELS

Models that can include dynamics of the Earth system, including feedbacks and biogeochemical cycling, gave a more detailed view of climate change and its impacts. Advancements in modeling at NCAR, NOAA, and other research centers around the world have ushered in a new era in understanding of our complex planet.

THE EFFECT OF CLIMATE CHANGE ON EXTREME WEATHER

A new branch of climate science, called attribution research, formed to study how global climate change affects extreme weather events such as heat waves, hurricanes, floods, and droughts. Each year since 2011, the Bulletin of the American Meteorological Society has issued a special report about extreme weather events during the past year and how the risk of severe weather has been altered by climate change.

INDIGENOUS CLIMATE KNOWLEDGE

Since 2012, the Rising Voices program has brought indigenous knowledge and western science together to improve understanding of climate change and other types of science and to develop strategies for resilient and sustainable communities.

"We need to appreciate the experience and knowledge that has been transferred from generation to generation to generation in Native American communities." - Bob Gough

EMISSIONS ARE THE HIGHEST IN HISTORY

The IPCC 5th Assessment Report noted that our influence on climate is clear and “recent anthropogenic emissions of greenhouse gases are the highest in history.” The report’s findings led to the Paris Climate Accord, in which nearly all of the world’s countries (174 countries in total) committed to actions limiting warming to below 2° Celsius (3.6° Fahrenheit) in an effort to avoid the most catastrophic impacts. (The United States announced in 2017 that it would back out of the agreement.)

CO2 STAYS ABOVE 400 PPM YEAR-ROUND

September is typically when carbon dioxide is at a minimum in its annual cycle. September 2016 was the first time that minimum level was over 400 parts per million. Before large-scale burning of fossil fuels, CO2 levels were about 280 ppm.

DWINDLING BIODIVERSITY

With Earth system models, scientists are now able to study how species and ecosystems around the world are likely to be affected by climate change and other human impacts. According to a 2019 United Nations report, climate change and other human impacts such as pollution and land use are threatening species worldwide. “Around 1 million species already face extinction, many within decades, unless action is taken,” according to the report.

CLIMATE MODELS ARE GETTING FUTURE WARMING PROJECTIONS RIGHT

Climate models have been making predictions since the 1970s, but are the predictions right? To find out, scientists ran 17 global climate models and compared the results with observed temperatures over the past half-century. Fourteen of the models predicted past temperatures accurately, which gives scientists confidence in the models’ ability to correctly project future warming.

2020 TIES WITH 2016 AS THE WARMEST YEAR ON RECORD

2016 and 2020 tied as the warmest years on record, according to 2021 reports. Scientists studying long-term temperature records found that the 10 warmest years through 2020 all occurred since 2000. From NASA Goddard Institute for Space Studies Director Gavin Schmidt, “…As the human impact on the climate increases, we have to expect that records will continue to be broken.“

ADVERSE IMPACTS ARE BEYOND NATURAL CLIMATE VARIABILITY

The Sixth Assessment Report highlights the impacts of human-induced climate change, including more frequent and intense extreme events. The changes have caused widespread adverse impacts and damages to nature and people, beyond what would be expected from natural climate variability.