Climate change warning signs started in the 1800s. Here's what humanity knew and when.

Political misinformation continues to swirl around the climate change discussion like a thick fog rolling in off the rising ocean. But a host of government documents and reports by researchers and historians lay a clear trail of what scientists and government officials knew and when.

Scientists had already figured out by the late 1800s that a greenhouse effect works to keep the planet warm, and that the carbon dioxide produced by burning coal could enhance that effect. By the 1970s, researchers were measuring those emissions in the atmosphere and warning Earth’s temperature could warm between 0.5 and 5 degrees Celsius by the mid-21st century.

Fifty years later, the vast majority of scientists agreed the global average temperature was already one degree Celsius higher than it had been in the late 1800s and had been rising at a rate of .2 degrees Celsius every decade since the 1970s.

Some people continue to wrongly characterize climate change as a new fad

Despite the long history of scientific and military documents that chronicle warming temperatures, rising sea levels and more extreme weather around the world, people often repeat misconceptions and share inaccurate information.

In one of the latest examples, presidential contender Ron DeSantis, governor of one of the states most vulnerable to climate change, brought up warming during a May 24 FOX News interview with Trey Gowdy.

When Gowdy asked about the U.S. military, DeSantis replied:

“You talk about things like global warming that they’re somehow concerned about, and that’s not the military I served in.”

But the military, including the Navy, has been worried about climate change for decades.

“DeSantis is wrong,” says Peter Gleick, a co-founder and senior fellow at the Pacific Institute, who has studied the U.S. military’s climate change research for more than 30 years.

Navy officials talked about the impacts of climate change more than 15 years before DeSantis joined the Navy in 2004.

• “We are all aware of possible threats posed by global climate change,” retired Navy Admiral James Watkins told members of Congress in February 1989, after being nominated by President George H.W. Bush to serve as Secretary of Energy.

• By 2001, Navy submarines had documented a “striking” thinning of new Arctic Ocean ice.

• The Navy conducted a two-day symposium in 2001 to evaluate potential operations needed in an ice-diminished Arctic.

• The Navy issued its “Climate Change Road Map” in 2010, the year DeSantis left active duty. It stated: “Climate change is a national security challenge with strategic implications for the Navy.”

What we knew and when about climate change

For more than 150 years, scientists have built on the work of others before them to identify the role of carbon dioxide emissions in warming the Earth.

“Any politician today that denies the reality of climate change is either grossly ignorant of more than a century of science or is deliberately misleading the public for political reasons,” Gleick said.

Read on to explore more about the roots of climate change research and the information scientists have learned and when:

Concerns about coal burning crop up early

1300s – King Edward of England bans coal burning, blaming it for thick, black smoke choking the air in London.

1700s – Coal-powered factories begin appearing in Great Britain as the first Industrial Revolution begins in Europe.

1824 – Jean-Baptiste Joseph Fourier, a mathematician and physicist in France, theorizes that certain gases in the atmosphere could trap heat from the sun.

1850s – Eunice Foote, an American scientist, demonstrates the ability of water vapor and carbon dioxide to affect solar heating, according to the National Oceanographic and Atmospheric Administration's Climate.gov website.

1861 – Irish physicist John Tyndall writes that water vapor and gasses such as carbon dioxide create the Earth’s greenhouse effect, trapping the Sun’s heat and keeping the planet warm.

1896 – Swedish scientist Svante Arrhenius publishes a study that shows he “knows that increasing carbon dioxide in the atmosphere will raise temperatures, and acknowledges that burning fossil fuels are a source of carbon dioxide, but stops just short of explicitly predicting man-made global warming,” said Robert Rohde, lead scientist for Berkeley Earth. Arrhenius connected the dots in his later work.

U.S. geologist Thomas Chamberlin at the University of Chicago, who studied glaciers in the Arctic, also writes about carbon dioxide’s role in regulating the Earth’s temperature.

1912 – A New Zealand newspaper warns burning coal could eventually change the climate. The piece was based on a Popular Mechanics magazine article published earlier that year that mentioned the work of Arrhenius.

Climate change conversation continues as research advances

The era from the 1950s to the 1970s ushers in more scientific progress and data collection.

1958 – Scientist C. David Keeling with the Scripps Institution of Oceanography begins direct measurements of carbon dioxide in the atmosphere at the Mauna Loa Observatory in Hawaii. In the 65 years since then, carbon dioxide concentrations have climbed from 315.98 parts per million to 423.78, a 34% increase.

1970 – Meteorologist George S. Benton at Johns Hopkins University writes "Carbon Dioxide and its Role in Climate Change" for the Proceedings of the National Academy of Sciences. He says:

• A 10% increase in carbon dioxide should result in an average temperature increase of about .3 degrees Celsius.

• Some local temperatures have warmed as much as 3-4 degrees Celsius.

1974 – The Central Intelligence Agency publishes the report “A Study of Climatological Research as it Pertains to Intelligence Problems.” The agency notes detrimental global climatic change and calls for more federally funded research, saying: “It is increasingly evident that the intelligence community must understand the magnitude of international threats which occur as a function of climatic change.”

1975 – Geochemist Wallace Broecker of Columbia University's Lamont-Doherty Geological Observatory publishes a study titled: "Climatic Change: Are We on the Brink of a Pronounced Global Warming?"

Research advances open information floodgates during Carter Administration 

By the late 1970s, the phrase “climate change” began regularly appearing in academic research papers, government reports and even newspaper stories.

After President Jimmy Carter’s election in 1976, several key developments occur, including a panel he commissioned to look at concentrations of carbon dioxide and a study for the Department of Energy.

1977 – In a July letter to Carter, his science adviser, geophysicist Frank Press, notes:

• Fossil fuel combustion has increased “at an exponential rate” over 100 years

• Carbon dioxide is 12% above the pre-industrial revolution level and could grow 1.5 to 2 times that level within 60 years, increasing warning anywhere from 0.5-5 degrees Celsius

• Rapid increase could be “catastrophic”

1978 – In one of the earliest references to climate change in the news media, Newsweek publishes a story by Peter Gwynne and Sharon Begley, during a tough winter, with heavy rain and mudslides in California.

• The authors asked if the Earth is moving into a period of colder weather and climatologists said climate change isn’t temporary weather but what happens over decades.

• “A growing number of meteorologists think that, rather than cooling, the atmosphere is actually warming up,” the story stated. And, "if the world is getting warmer, the main reason is a rise in the atmosphere’s level of carbon dioxide.”

July 1980 – The Global 2000 Study Report to the President, written by a team co-led by Martha Garrett and Gerald Barney, moves the conversation about environmental challenges fully into American politics. Among its findings:

• Even a 1 degree Celsius rise would make the earth’s climate warmer than in 1,000 years

• A carbon dioxide-induced temperature rise is expected to be 3 or 4 times greater at the poles than in the middle latitudes. (Today, federal officials say the Arctic is warming more than twice as fast as anywhere else in the world and at an even greater pace in some locations and at some times of the year.)

December 1980 – The probable outcome of the concentration of CO2 in the atmosphere is “beyond human experience,” reports a sweeping study by the American Association for the Advancement of Science for the Energy Department. The report states, that CO2-triggered climate change could:

• Cause floods and droughts, leading to malnutrition and famine.

• "Pit nation against nation and group against group.''

Roger Revelle, former president of the American Association for the Advancement of Science, says if carbon dioxide levels doubled by mid-21st century, average global temperatures would increase by 5 degrees Fahrenheit, the Associated Press reports.

1988 – James Hansen, with NASA’s Goddard Space Institute, and George Woodwell, director of the Woods Hole Research Center, tell members of the U.S. Senate’s Energy and Natural Resources committee that carbon dioxide levels in the atmosphere are rising and responsible for increases in global average temperature and warming at higher latitudes.

1989 – The National Academy of Sciences — now led by Press, Carter's former science adviser — sends a letter to President-elect George H.W. Bush, urging him to place the threat of increasing global temperatures high on his agenda and to seek alternatives to coal, oil and other pollutants that fuel global warming.

Gleick publishes a study that notes widespread attention to concerns about how climate change and other environmental problems could affect international security and recommends responses to minimize adverse consequences.

1990 – The U.S. Navy War College presents a report to the Select Senate Committee on Intelligence, “Global Climate Change: Implications for the United States.” in what Gleick says is the first explicit acknowledgement of the potential threat of climate change to national security.

1991 – The Bush administration’s National Security Strategy of the United States mentions the climate peril twice, saying environmental concerns such as climate change and deforestation were “already contributing to political conflict.”

1997 – Members of the United Nations Framework Convention on Climate Change adopt the Kyoto Protocol in Kyoto, Japan in December. It receives 84 signatures over the next 15 months.

1998 – The federal government declassifies data gathered by Navy submarines on Arctic sea ice thickness, information deemed essential to examining how global climate change affects ice cover.

1999 –  As the millennium closes, researchers Michael Mann, Raymond Bradley and Malcolm Hughes reconstruct historical temperatures and suggest warming in the latter half of the century is unlike anything in at least 1,000 years. It became widely known as the hockey stick theory, for the line that shows the abrupt increase in later years.

A new century

2002 – The National Academies of Science releases the report: “Abrupt Climate Change, Inevitable Surprises.”

2003 – Abrupt climate change could pose “specific consequences to the US military,” writes retired Navy Rear Admiral Richard Pittenger and oceanographer Robert Gagosian in a piece for Defense Horizons. They say it “seems a useful exercise to contemplate the military ramifications of potential, abrupt climate changes."

2009 – U.S. Navy creates a Climate Change Task Force to recommend actions the Navy should take in response to sudden changes in the Arctic marine environment. Rear Admiral David Titley, who led the task force, later said counter arguments presented during the research “fell apart in the face of overwhelming evidence.”

By 2010, the task force releases an “Arctic Roadmap” and a Navy Climate Change roadmap. Among the statements:

• Arctic is warming twice as fast as the rest of the globe.

• “The current scientific consensus indicates the Arctic may experience nearly ice free summers sometime in the 2030's.”

• Climate change is "affecting military installations and access to natural resources worldwide.”

2015 – An Inside Climate News investigation reports Exxon and Exxon Mobil Corp. accurately predicted human caused global warming between 1977 and 2003 but "suppressed the information"

2019 – A Department of Defense report during the administration of President Donald Trump says dozens of bases are experiencing climate change challenges, including rising sea levels, thawing permafrost, drought and wildfires.

2021 – Department of Defense risk analysis warns “to keep the nation secure, we must tackle the existential threat of climate change. The unprecedented scale of wildfires, floods, droughts, typhoons, and other extreme weather events of recent months and years have damaged our installations and bases, constrained force readiness and operations, and contributed to instability around the world.”

In June 2023, Titley, the retired rear admiral who led the Navy's 2009-10 task force, told USA TODAY the military is "always interested in changes (political, economic, demographic, agricultural, engineering, technology, etc) that will impact war fighting, readiness, and the capabilities of both ourselves and any potential adversaries."

When people asked him why the military would be interested in climate change, Titley said he responded with his own question. “Why wouldn’t we be if it impacting warfighting and readiness? It would be negligent and a disservice of our Soldiers, Sailors, Airmen and Marines not to think through the changes that will be caused by a changing climate."

This article originally appeared on USA TODAY: Timeline of climate change: What humanity knew and when