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Climate change is the long-term alteration in Earth’s climate and weather patterns. It took nearly a century of research and data to convince the vast majority of the scientific community that human activity could alter the climate of our entire planet. In the 1800s, experiments suggesting that human-produced carbon dioxide (CO2) and other gases could collect in the atmosphere and insulate Earth were met with more curiosity than concern. By the late 1950s, CO2 readings would offer some of the first data to corroborate the global warming theory. Eventually an abundance of data, along with climate modeling would show not only that global warming was real, but that it also presented a host of dire consequences.
Early Inklings That Humans Can Alter Global Climate
Dating back to the ancient Greeks, many people had proposed that humans could change temperatures and influence rainfall by chopping down trees, plowing fields or irrigating a desert.
One theory of climate effects, widely believed until the Dust Bowl of the 1930s, held that “rain follows the plow,” the now-discredited idea that tilling soil and other agricultural practices would result in increased rainfall.
Accurate or not, those perceived climate effects were merely local. The idea that humans could somehow alter climate on a global scale would seem far-fetched for centuries.
WATCH: How the Earth Was Made on HISTORY Vault.
The Greenhouse Effect
In the 1820s, French mathematician and physicist Joseph Fourier proposed that energy reaching the planet as sunlight must be balanced by energy returning to space since heated surfaces emit radiation. But some of that energy, he reasoned, must be held within the atmosphere and not return to space, keeping Earth warm.
He proposed that Earth’s thin covering of air—its atmosphere—acts the way a glass greenhouse would. Energy enters through the glass walls, but is then trapped inside, much like a warm greenhouse.
Experts have since pointed out that the greenhouse analogy was an oversimplification, since outgoing infrared radiation isn’t exactly trapped by Earth’s atmosphere but absorbed. The more greenhouse gases there are, the more energy is kept within Earth’s atmosphere.
But the so-called greenhouse effect analogy stuck and some 40 years later, Irish scientist John Tyndall would start to explore exactly what kinds of gases were most likely to play a role in absorbing sunlight.
Tyndall’s laboratory tests in the 1860s showed that coal gas (containing CO2, methane and volatile hydrocarbons) was especially effective at absorbing energy. He eventually demonstrated that CO2 alone acted like sponge in the way it could absorb multiple wavelengths of sunlight.
By 1895, Swedish chemist Svante Arrhenius became curious about how decreasing levels of CO2 in the atmosphere might cool Earth. In order to explain past ice ages, he wondered if a decrease in volcanic activity might lower global CO2 levels. His calculations showed that if CO2 levels were halved, global temperatures could decrease by about 5 degrees Celsius (9 degrees Fahrenheit).
Next, Arrhenius wondered if the reverse were true. Arrhenius returned to his calculations, this time investigating what would happen if CO2 levels were doubled. The possibility seemed remote at the time, but his results suggested that global temperatures would increase by the same amount—5 degrees C or 9 degrees F.
Decades later, modern climate modeling have confirmed that Arrhenius’ numbers weren’t far off the mark.
Welcoming a Warmer Earth
Back in the 1890s, however, the concept of warming the planet was remote and even welcomed.
As Arrehenius wrote, “By the influence of the increasing percentage of carbonic acid [CO2] in the atmosphere, we may hope to enjoy ages with more equable and better climates, especially as regards the colder regions of the earth.”
By the 1930s, at least one scientist would start to claim that carbon emissions might already be having a warming effect. British engineer Guy Stewart Callendar noted that the United States and North Atlantic region had warmed significantly on the heels of the Industrial Revolution.
Callendar’s calculations suggested that a doubling of CO2 in Earth’s atmosphere could warm Earth by 2 degrees C (3.6 degrees F). He would continue to argue into the 1960s that a greenhouse-effect warming of the planet was underway.
While Callendar’s claims were largely met with skepticism, he managed to draw attention to the possibility of global warming. That attention played a part in garnering some of the first government-funded projects to more closely monitor climate and CO2 levels.
Most famous among those research projects was a monitoring station established in 1958 by the Scripps Institution of Oceanography on top of Hawaii’s Mauna Loa Observatory.
Scripps geochemist Charles Keeling was instrumental in outlining a way to record CO2 levels and in securing funding for the observatory, which was positioned in the center of the Pacific Ocean.
Data from the observatory revealed what would become known as the “Keeling Curve.” The upward, saw tooth-shaped curve showed a steady rise in CO2 levels, along with short, jagged up-and-down levels of the gas produced by repeated wintering and greening of the Northern Hemisphere.
The dawn of advanced computer modeling in the 1960s began to predict possible outcomes of the rise in CO2 levels made evident by the Keeling Curve. Computer models consistently showed that a doubling of CO2 could produce a warming of 2 degrees C or 3.6 degrees F within the next century.
Still, the models were preliminary and a century seemed a very long time away.
READ MORE: When Global Warming Was Revealed by the Keeling Curve
1970s Scare: A Cooling Earth
In the early 1970s, a different kind of climate worry took hold: global cooling. As more people became concerned about pollutants people were emitting into the atmosphere, some scientists theorized the pollution could block sunlight and cool Earth.
In fact, Earth did cool somewhat between 1940-1970 due to a postwar boom in aerosol pollutants which reflected sunlight away from the planet. The idea that sunlight-blocking pollutants could chill Earth caught on in the media, as in a 1974 Time magazine article titled “Another Ice Age?”
But as the brief cooling period ended and temperatures resumed their upward climb, warnings by a minority of scientists that Earth was cooling were dropped. Part of the reasoning was that while smog could remain suspended in the air for weeks, CO2 could persist in the atmosphere for centuries.
1988: Global Warming Gets Real
The early 1980s would mark a sharp increase in global temperatures. Many experts point to 1988 as a critical turning point when watershed events placed global warming in the spotlight.
The summer of 1988 was the hottest on record (although many since then have been hotter). 1988 also saw widespread drought and wildfires within the United States.
Scientists sounding the alarm about climate change began to see media and the public paying closer attention. NASA scientist James Hansen delivered testimony and presented models to congress in June of 1988, saying he was “99 percent sure” that global warming was upon us.
One year later, in 1989, the Intergovernmental Panel on Climate Change (IPCC) was established under the United Nations to provide a scientific view of climate change and its political and economic impacts.
As global warming gained currency as a real phenomenon, researchers dug into possible ramifications of a warming climate. Among the predictions were warnings of severe heat waves, droughts and more powerful hurricanes fueled by rising sea surface temperatures.
Other studies predicted that as massive glaciers at the poles melt, sea levels could rise between 11 and 38 inches (28 to 98 centimeters) by 2100, enough to swamp many of the cities along the east coast of the United States.
Kyoto Protocol: United States In, Then Out
Government leaders began discussions to try and stem the outflow of greenhouse gas emissions to prevent the most dire predicted outcomes. The first global agreement to reduce greenhouse gases, the Kyoto Protocol, was adopted in 1997.
The protocol, which was signed by President Bill Clinton, called for reducing the emission of six greenhouse gases in 41 countries plus the European Union to 5.2 percent below 1990 levels during the target period of 2008 to 2012.
In March 2001, shortly after taking office, President George W. Bush announced the United States would not implement the Kyoto Protocol, saying the protocol was “fatally flawed in fundamental ways” and citing concerns that the deal would hurt the U.S. economy.
An Inconvenient Truth
That same year, the IPCC issued its third report on climate change, saying that global warming, unprecedented since the end of the last ice age, is “very likely,” with highly damaging future impacts. Five years later, in 2006, former Vice President and presidential candidate Al Gore weighed in on the dangers of global warming with the debut of his film An Inconvenient Truth. Gore won the 2007 Nobel Peace Prize for his work on behalf of climate change.
Politicization over climate change, however, would continue, with some skeptics arguing that predictions presented by the IPCC and publicized in media like Gore’s film were overblown.
Among those expressing skepticism over global warming was future U.S. president Donald Trump. On November 6, 2012, Trump tweeted “The concept of global warming was created by and for the Chinese in order to make U.S. manufacturing non-competitive.”
Paris Climate Agreement: United States In, Then Out
The United States, under President Barack Obama, would sign onto another milestone treaty on climate change, the Paris Climate Agreement, in 2015. In that agreement, 197 countries pledged to set targets for their own greenhouse gas cuts and to report their progress.
The backbone of the Paris Climate Agreement was a declaration to prevent a global temperature rise of 2 degrees C (3.6 degrees F). Many experts considered 2 degrees C of warming to be a critical limit, which, if surpassed will lead to increasing risk of more deadly heat waves, droughts, storms and rising global sea levels.
The election of Donald Trump in 2016 led to the United States declaring it would withdraw from the Paris treaty. President Trump, citing the “onerous restrictions” imposed by the accord, stated that he could not “in good conscience support a deal that punishes the United States.”
That same year, independent analyses by NASA and the National Oceanic and Atmospheric Administration (NOAA) found Earth’s 2016 surface temperatures to be the warmest since modern record keeping began in 1880. And in October 2018, the U.N.'s Intergovernmental Panel on Climate Change issued a report that concluded "rapid, far-reaching" actions are needed to cap global warming at 1.5 Celsius (2.7 Fahrenheit) and avert the most dire, irreversible consequences for the planet.
Greta Thunberg and Climate Strikes
In August 2018, Swedish teenager and climate activist Greta Thunberg began protesting in front of Swedish Parliament with a sign: “School Strike for Climate.” Her protest to raise awareness for global warming caught the world by storm and by November 2018, over 17,000 students in 24 countries were participating in climate strikes. By March 2019, Thunberg was nominated for a Nobel Peace Prize. She participated in the United Nations Climate Summit in New York City in August of 2019, famously taking a boat across the Atlantic instead of flying to reduce her carbon footprint.
The UN Climate Action Summit reinforced d that “1.5℃ is the socially, economically, politically and scientifically safe limit to global warming by the end of this century,” and set a deadline for achieving net zero emissions to 2050.
The Discovery of Global Warming, by Spencer R. Weart. (Harvard University Press, 2008).
The Thinking Person’s Guide to Climate Change, by Robert Henson. (AMS Books, 2014).
“Another Ice Age?” Time.
“Why we know about the greenhouse gas effect” Scientific American.
The History of the Keeling Curve, Scripps Institute of Oceanography.
Remembering the Drought of 1988, NASA Earth Observatory.
Sea Level Rise, National Geographic/reference.
“Guy Stewart Callendar: Global warming discovery marked,” BBC News.
President Bush Discusses Global Climate Change, The White House, President George W. Bush.
“Why the Paris talks won’t prevent 2 degrees of global warming,” PBS News Hour.
Statement by President Trump on the Paris Climate Accord, The White House.
“Trump Will Withdraw U.S. From Paris Climate Agreement,” The New York Times.
“NASA, NOAA Data Show 2016 Warmest Year on Record Globally,” NASA.
How Did We Get Here?
Today, atmospheric CO2 is at a level that has not been seen on Earth for at least 800,000 years, and probably much longer.
Coal and heat
By the 1600s, coal was replacing wood as a common fuel. In addition to being readily available, coal had another great advantage over wood: it is more energy-dense. That is, it takes less coal than wood to produce an equivalent amount of heat.
Coal and transportation
The early 1800s saw the invention of boilers that could hold steam under high pressure. Within decades, these boilers were driving more powerful coal-fired engines that could pull heavy trains and power steamboats. A steam-powered ship first crossed the Atlantic Ocean in 1833.
The World Gets Wheels
The first mass-produced Model T Ford left the factory in 1908 by 1915 Ford was selling 500,000 a year. Most were powered by oil, although these internal combustion engines were also capable of running on ethanol, a plant-based fuel. Oil eventually became the fuel of choice for engines designed to move from place to place.
On The Move
There were fewer than 50,000 cars and trucks on the world's roads in 1900. By 2000, there were more than 700 million. And personal mobility is only gaining in appeal in 2008, Indian automakers unveiled an inexpensive five-seater car with a small, 33-horsepower engine. They expect annual demand of up to one million cars.
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.
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
Estimated world population: 813 million–1.1 billion
Estimated size of world economy: $175 billion
Estimated atmospheric carbon dioxide: 284 ppm
Estimated world population: 1.1–1.4 billion
Estimated size of world economy: $360 billion
Estimated atmospheric carbon dioxide: 286 ppm
Estimated world population: 1.5–1.8 billion
Estimated size of world economy: $1.1 trillion
Estimated atmospheric carbon dioxide: 300 ppm
Estimated world population: 2.4–2.6 billion
Estimated size of world economy: $4.1 trillion
Estimated atmospheric carbon dioxide: 311 ppm
Estimated world population: 6.07 billion
Estimated size of world economy: $41 trillion
Estimated atmospheric CO2 in 2000: 369 ppm
Estimated atmospheric CO2: 385 ppm
This isn't the first time Earth's climate has changed, but it's the first time human activity has caused it. Learn more about global warming and how—and why—we should slow it.
Think you're an expert on our changing climate? Test your knowledge with this interactive quiz.
A brief history of climate change
1712 - British ironmonger Thomas Newcomen invents the first widely used steam engine, paving the way for the Industrial Revolution and industrial scale use of coal.
1800 - World population reaches one billion.
1824 - French physicist Joseph Fourier describes the Earth's natural "greenhouse effect". He writes: "The temperature [of the Earth] can be augmented by the interposition of the atmosphere, because heat in the state of light finds less resistance in penetrating the air, than in re-passing into the air when converted into non-luminous heat."
1861 - Irish physicist John Tyndall shows that water vapour and certain other gases create the greenhouse effect. "This aqueous vapour is a blanket more necessary to the vegetable life of England than clothing is to man," he concludes. More than a century later, he is honoured by having a prominent UK climate research organisation - the Tyndall Centre - named after him.
1886 - Karl Benz unveils the Motorwagen, often regarded as the first true automobile.
1896 - Swedish chemist Svante Arrhenius concludes that industrial-age coal burning will enhance the natural greenhouse effect. He suggests this might be beneficial for future generations. His conclusions on the likely size of the "man-made greenhouse" are in the same ballpark - a few degrees Celsius for a doubling of CO2 - as modern-day climate models.
1900 - Another Swede, Knut Angstrom, discovers that even at the tiny concentrations found in the atmosphere, CO2 strongly absorbs parts of the infrared spectrum. Although he does not realise the significance, Angstrom has shown that a trace gas can produce greenhouse warming.
1927 - Carbon emissions from fossil fuel burning and industry reach one billion tonnes per year.
1930 - Human population reaches two billion.
1938 - Using records from 147 weather stations around the world, British engineer Guy Callendar shows that temperatures had risen over the previous century. He also shows that CO2 concentrations had increased over the same period, and suggests this caused the warming. The "Callendar effect" is widely dismissed by meteorologists.
1955 - Using a new generation of equipment including early computers, US researcher Gilbert Plass analyses in detail the infrared absorption of various gases. He concludes that doubling CO2 concentrations would increase temperatures by 3-4C.
1957 - US oceanographer Roger Revelle and chemist Hans Suess show that seawater will not absorb all the additional CO2 entering the atmosphere, as many had assumed. Revelle writes: "Human beings are now carrying out a large scale geophysical experiment. "
1958 - Using equipment he had developed himself, Charles David (Dave) Keeling begins systematic measurements of atmospheric CO2 at Mauna Loa in Hawaii and in Antarctica. Within four years, the project - which continues today - provides the first unequivocal proof that CO2 concentrations are rising.
1960 - Human population reaches three billion.
1965 - A US President's Advisory Committee panel warns that the greenhouse effect is a matter of "real concern".
1972 - First UN environment conference, in Stockholm. Climate change hardly registers on the agenda, which centres on issues such as chemical pollution, atomic bomb testing and whaling. The United Nations Environment Programme (Unep) is formed as a result.
1975 - Human population reaches four billion.
1975 - US scientist Wallace Broecker puts the term "global warming" into the public domain in the title of a scientific paper.
1987 - Human population reaches five billion
1987 - Montreal Protocol agreed, restricting chemicals that damage the ozone layer. Although not established with climate change in mind, it has had a greater impact on greenhouse gas emissions than the Kyoto Protocol.
1988 - Intergovernmental Panel on Climate Change (IPCC) formed to collate and assess evidence on climate change.
1989 - UK Prime Minister Margaret Thatcher - possessor of a chemistry degree - warns in a speech to the UN that "We are seeing a vast increase in the amount of carbon dioxide reaching the atmosphere. The result is that change in future is likely to be more fundamental and more widespread than anything we have known hitherto." She calls for a global treaty on climate change.
1989 - Carbon emissions from fossil fuel burning and industry reach six billion tonnes per year.
1990 - IPCC produces First Assessment Report. It concludes that temperatures have risen by 0.3-0.6C over the last century, that humanity's emissions are adding to the atmosphere's natural complement of greenhouse gases, and that the addition would be expected to result in warming.
1992 - At the Earth Summit in Rio de Janeiro, governments agree the United Framework Convention on Climate Change. Its key objective is "stabilization of greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system". Developed countries agree to return their emissions to 1990 levels.
1995 - IPCC Second Assessment Report concludes that the balance of evidence suggests "a discernible human influence" on the Earth's climate. This has been called the first definitive statement that humans are responsible for climate change.
1997 - Kyoto Protocol agreed. Developed nations pledge to reduce emissions by an average of 5% by the period 2008-12, with wide variations on targets for individual countries. US Senate immediately declares it will not ratify the treaty.
1998 - Strong El Nino conditions combine with global warming to produce the warmest year on record. The average global temperature reached 0.52C above the mean for the period 1961-90 (a commonly used baseline).
1998 - Publication of the controversial "hockey stick" graph indicating that modern-day temperature rise in the northern hemisphere is unusual compared with the last 1,000 years. The work would later be the subject of two enquiries instigated by the US Congress.
1999 - Human population reaches six billion.
2001 - President George W Bush removes the US from the Kyoto process.
2001 - IPCC Third Assessment Report finds "new and stronger evidence" that humanity's emissions of greenhouse gases are the main cause of the warming seen in the second half of the 20th Century.
2005 - The Kyoto Protocol becomes international law for those countries still inside it.
2005 - UK Prime Minister Tony Blair selects climate change as a priority for his terms as chair of the G8 and president of the EU.
2006 - The Stern Review concludes that climate change could damage global GDP by up to 20% if left unchecked - but curbing it would cost about 1% of global GDP.
2006 - Carbon emissions from fossil fuel burning and industry reach eight billion tonnes per year.
2007 - The IPCC's Fourth Assessment Report concludes it is more than 90% likely that humanity's emissions of greenhouse gases are responsible for modern-day climate change.
2007 - The IPCC and former US vice-president Al Gore receive the Nobel Peace Prize "for their efforts to build up and disseminate greater knowledge about man-made climate change, and to lay the foundations for the measures that are needed to counteract such change".
2007 - At UN negotiations in Bali, governments agree the two-year "Bali roadmap" aimed at hammering out a new global treaty by the end of 2009.
A brief history of climate change Duplicate 1
Companies have a fundamental responsibility to reduce their impact on the planet and join the journey to a decarbonized economy. At MSCI, we want to lead by example.
To achieve this goal throughout MSCI’s global operations, MSCI has committed to achieve net-zero emissions before 2040.
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The last deglaciation
The continental ice sheets began to melt back about 20,000 years ago. Drilling and dating of submerged fossil coral reefs provide a clear record of increasing sea levels as the ice melted. The most rapid melting began 15,000 years ago. For example, the southern boundary of the Laurentide Ice Sheet in North America was north of the Great Lakes and St. Lawrence regions by 10,000 years ago, and it had completely disappeared by 6,000 years ago.
The warming trend was punctuated by transient cooling events, most notably the Younger Dryas climate interval of 12,900–11,600 years ago. The climatic regimes that developed during the deglaciation period in many areas, including much of North America, have no modern analog (i.e., no regions exist with comparable seasonal regimes of temperature and moisture). For example, in the interior of North America, climates were much more continental (that is, characterized by warm summers and cold winters) than they are today. Also, paleontological studies indicate assemblages of plant, insect, and vertebrate species that do not occur anywhere today. Spruce trees grew with temperate hardwoods (ash, hornbeam, oak, and elm) in the upper Mississippi River and Ohio River regions. In Alaska, birch and poplar grew in woodlands, and there were very few of the spruce trees that dominate the present-day Alaskan landscape. Boreal and temperate mammals, whose geographic ranges are widely separated today, coexisted in central North America and Russia during this period of deglaciation. These unparalleled climatic conditions probably resulted from the combination of a unique orbital pattern that increased summer insolation and reduced winter insolation in the Northern Hemisphere and the continued presence of Northern Hemisphere ice sheets, which themselves altered atmospheric circulation patterns.
History of Climate Change DebateClick for an Encyclopaedia Britannica video about the impact of greenhouse-gas emissions on Earth’s temperature
Average surface temperatures on earth have risen more than 2°F over the past 100 years.  During this time period, atmospheric levels of greenhouse gases such as carbon dioxide (CO2) and methane (CH4) have notably increased.  This site explores the debate on whether climate change is caused by humans (also known as anthropogenic climate change).
The pro side argues rising levels of atmospheric greenhouse gases are a direct result of human activities such as burning fossil fuels, and that these increases are causing significant and increasingly severe climate changes including global warming, loss of sea ice, sea level rise, stronger storms, and more droughts. They contend that immediate international action to reduce greenhouse gas emissions is necessary to prevent dire climate changes.
The con side argues human-generated greenhouse gas emissions are too small to substantially change the earth’s climate and that the planet is capable of absorbing those increases. They contend that warming over the 20th century resulted primarily from natural processes such as fluctuations in the sun’s heat and ocean currents. They say the theory of human-caused global climate change is based on questionable measurements, faulty climate models, and misleading science.
Early Science on Greenhouse Gasses and Climate ChangeCarbon dioxide (CO2) is released and absorbed in the global carbon cycle.
Source: United States Department of Energy “Simplified Global Carbon Cycle,” genomics.energy.gov (accessed June 2, 2010)
Scientists have known of the heating potential (greenhouse effect) of gases such as CO2 since at least 1859, when Irish physicist John Tyndall first began experiments leading to the discovery that CO2 in the atmosphere absorbs the sun’s heat. 
On Feb. 16, 1938, engineer Guy S. Callendar published an influential study suggesting increased atmospheric CO2 from fossil fuel combustion was causing global warming.  Many scientists at that time were skeptical of Callendar’s conclusion, arguing that that natural fluctuations and atmospheric circulation changes determined the climate, not CO2 emissions. 
In Mar. 1958, US climate scientist Charles Keeling began measuring atmospheric CO2 at the Mauna Loa observatory in Hawaii for use in climate modeling.  Using these measurements, Keeling became the first scientist to confirm that atmospheric CO2 levels were rising rather than being fully absorbed by forests and oceans (carbon sinks).  When Keeling began his measurements, atmospheric CO2 levels stood at 315 parts per million (ppm). 
The US National Academy of Sciences issued a 1977 report titled “Energy and Climate” that concluded the burning of fossil fuels was increasing atmospheric CO2, and that increased CO2 was associated with a rise in global temperatures. Image of protesters at the Sep. 20, 2019 Climate Strike in Sydney, Australia. Photo by Jenny Evans/Getty.
Source: Laura Parker, “Listen and Help Us: Kids Worldwide Are on Strike for the Climate,” www.nationalgeographic.com.au, Sep. 22, 2019
On June 23, 1988 National Aeronautics and Space Administration (NASA) scientist James Hansen presented testimony to the US Senate stating that increases in CO2 were warming the planet and “changing our climate.”  At the time, MIT meteorologist Richard Lindzen criticized these findings, arguing that computerized climate models were unreliable and that natural processes would balance out any warming caused by increased CO2. 
Formation of the IPCC and the UN Framework Convention on Climate Change
The Intergovernmental Panel on Climate Change (IPCC) was created in 1988 by the World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP) to review research on global climate change (as of Mar. 2020, there were 195 IPCC member countries).  The IPCC issued its first assessment report in 1990 stating that “emissions resulting from human activities are substantially increasing the atmospheric concentrations of the greenhouse gases,” resulting in “an additional warming of the Earth’s surface.” 
The United Nations Framework Convention on Climate Change (UNFCCC) was signed by US President George H.W. Bush on Oct. 13, 1992.  The goal of the convention was the “stabilization of greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system.”  The UNFCCC became the parent treaty for the 1997 Kyoto Protocol and the 2015 Paris Agreement. 
Source: 1.bp.blogspot.com (accessed June 11, 2010)
Kyoto Protocol, Paris Agreement, and Other International Conferences on Climate Change
Over 161 nations met in Kyoto, Japan, in Dec. 1997 to negotiate a treaty to limit greenhouse gas emissions and work toward the objectives of the UNFCCC. The resulting Kyoto Protocol,  signed by President Bill Clinton, set binding targets for 37 industrialized countries and the European Union to reduce greenhouse gas emissions roughly 5% below 1990 levels by 2012. 
President George W. Bush withdrew the United States from the Kyoto Protocol in Mar. 2001 due to Senate opposition and concerns that limiting greenhouse gas emissions would harm the US economy. From July 16-27, 2001 the COP 6 conference (conference of signatory parties to the UNFCCC) took place in Bonn, Germany, and the final amendments to the Kyoto Protocol were made. 179 countries reached a binding agreement without US participation. 
On Mar. 2, 2008 the Heartland Institute sought to challenge the idea that human activity was causing climate change by holding its own international conference on climate change. At the conference, 98 speakers including PhD climate scientists from major universities argued that global warming was most likely a natural event. 
In Dec. 2009 the COP 15 conference took place in Copenhagen, Denmark. The resulting Copenhagen Accord, signed by 114 nations including the United States and China, called for “deep cuts” in human greenhouse gas emissions in order to make sure that earth’s temperature rises no more than 1.5°C above pre-industrial levels. 
In Dec. 2015, the COP 21 met in Paris where 195 countries, including the United States, adopted the Paris Agreement.  The agreement’s central aim was to prevent global temperatures from rising more than 1.5°C – 2°C above pre-industrial levels. Under the agreement, all countries were required to create a national plan to reduce greenhouse gas emissions and report regularly on their individual progress towards meeting their emission reduction goals.  President Obama, still in office at the time, called the agreement a “turning point for the world” that “establishes the enduring framework the world needs to solve the climate crisis.” 
On June 1, 2017, President Trump announced his intention to withdraw the United States from the Paris Agreement and ordered the federal government to “cease all implementation” of the agreement. President Trump said the Paris Agreement had imposed “draconian financial and economic burdens” on the United States and created “serious obstacles” to energy development.  On Nov. 7, 2017, during the COP 23 UN climate talks in Bonn, Germany, Syria announced that it would sign the Paris agreement on climate change, leaving the United States as the only country that has rejected the global pact.  The United States officially left the Paris Climate Agreement on Nov. 4, 2020. 
On inauguration day (Jan. 20, 2021), President Joe Biden released a statement rejoining the Paris Climate Agreement. The United States officially rejoined the agreement 30 days later on Feb. 19, 2021.   
US Debate over Climate Change Heats Up
Al Gore’s documentary An Inconvenient Truth premiered in 2006 and was seen by over 5 million people worldwide. The film warned that human-caused climate change was real, and that without immediate reductions in greenhouse gas emissions, catastrophic climate changes would severely disrupt human societies, leading to a possible collapse of industrial civilization. 
A IPCC assessment report stated that climate change was accelerating, which could lead to more war and conflict around the world, and the report called for urgent counter-measures to be implemented.  The IPCC and Al Gore jointly received the 2007 Noble Peace Prize “for their efforts to build up and disseminate greater knowledge about man-made climate change.”  In response to the IPCC findings, a group of scientists formed the Nongovernmental International Panel on Climate Change (NIPCC) to compile a report challenging the science behind man-made climate change. Their Mar. 2, 2008 report, “Nature, Not Human Activity, Rules the Climate,” was published by the Heartland Institute. 
Between 1998 and 2009, the United States allocated $99 billion to federal agencies for work related to climate change. During that period there was a big uptick in climate-related technology development while spending on climate science remained about the same. 
On Apr. 2, 2007, the US Supreme Court ruled (5-4) in Massachusetts v. EPA that greenhouse gases met the criteria to be considered pollutants under the Clean Air Act.  In response, the US EPA announced in 2009 that greenhouse gases “threaten public health” and are “the primary driver of climate change.”  In its June 23, 2014 decision in Utility Air Regulatory Group v. EPA, the US Supreme Court upheld the EPA’s authority to regulate greenhouse gas emissions from stationary sources such as power plants. Graph showing that Arctic air temperature (blue line) parallels natural solar activity (red line).
Source: Oregon Institute of Science and Medicine, “Environmental Effects of Increased Atmospheric Carbon Dioxide,” Journal of American Physicians and Surgeons, Fall 2007
On Sep. 21, 2014 the largest climate march to date took place in New York, NY, as over 400,000 people marched to demand that world governments take immediate action to reduce greenhouse gas emissions.  In Mar. 2019, as many as 1.4 million people worldwide participated in a school walk out to bring attention to climate change.  The student movement started by Swedish climate activist Greta Thunberg continued on Sep. 20, 2019 with an estimated four million demonstrators in at least 160 countries calling for action on climate change, an event that is thought to be the largest climate protest in history to that point. 
The Obama Administration enacted the strictest passenger vehicle fuel efficiency standards in US history as part of a plan to address climate change. The CO2 standards set in 2012 required an annual 5% increase in fuel efficiency to reach 54.5 miles per gallon by 2025.  On Mar. 31, 2020, the Trump Administration lowered the requirement to a 1.5% increase each year towards a goal of 40 miles per gallon on average by 2026.  An analysis by Rhodium Group predicted the lowered standards would result in about 20% of the reduction in greenhouse gas emissions that were expected under the Obama-era standards. 
How Will Climate Change Affect Us?
According to NOAA’s National Climatic Data Center, 2014 was the hottest year on record across the globe since 1880 when record keeping began.  The following five years were even warmer as 2016 set the record for hottest year ever and global average temperatures in 2019 were the second-hottest as of Mar. 2020. 
In 2019, CO2 levels were 415.3 ppm, up from 315.7 ppm when measurements began in 1958.   These CO2 levels are reportedly higher than at any time in the last 650,000 years when levels fluctuated between 180 and 300 ppm. 
The Unites States makes up about 4% of the world’s population but was responsible for nearly one-third of historical global greenhouse gas emissions.  In 2018, global emissions of human-produced CO2 were about 37 billion tons. The greenhouse effect illustrated.
Source: US Environmental Protection Agency (EPA), “Frequently Asked Questions about Global Warming and Climate Change: Back to Basics,” epa.gov (accessed Mar. 12, 2015)
Predictions about how climate changes would affect civilization ranged from a Department of Defense report  detailing catastrophic weather events and a “significant drop in the human carrying capacity of the Earth’s environment,” to an Oregon Institute of Science and Health report detailing “an increasingly lush environment of plants and animals.” 
The question of how climate change impacts extreme weather came to the forefront of public debate when wildfires raged across Australia for 240 days from 2019 through early 2020. A World Weather Attribution study found that climate change increased the likelihood of wildfires such as those in Australia by at least 30% since 1900.  William Reville, emeritus professor of biochemistry at University College Cork, noted that other factors also contributed to the fires, such as failing to clear undergrowth and leaves that fuel the fires, a shortage of skilled firefighters, population density, and arson. 
Ongoing IPCC Findings, National Climate Assessment, and Counterpoints
On Sep. 27, 2013 the IPCC announced that it is now “extremely likely [95% confidence] that human influence has been the dominant cause of the observed warming since the mid-20th century.” 
The Heartland Institute argued against human-caused global warming in its 2013 NIPCC report which said that global warming since 1860 is the result of natural “cycles driven by ocean-atmosphere oscillations, or by solar variations.” 
The US Global Change Research Program released the 2014 National Climate Assessment on May 6, 2014. The report called climate change “a global public health problem,” stated that climate change impacts are already “visible in every state,” and concluded that human-induced “climate change is happening now.”  The report was criticized by some members of Congress, including US Senator James Inhofe (R-OK), who stated that “we can all agree that natural variations in the climate are taking place, but man-made global warming still remains a theory.” 
In Nov. 2018, Volume II of the 4th National Climate Assessment was published. It concluded, in part, that “rising temperatures, extreme heat, drought, wildfire on rangelands, and heavy downpours” are expected to increase and that “[w]ithout adaptation, climate change will continue to degrade infrastructure performance over the rest of the century, with the potential for cascading impacts that threaten our economy, national security, essential services, and health and well-being.”  The Trump administration criticized the report, stating that “it’s not based on facts… It’s not data-driven. We’d like to see something that is more data-driven. It’s based on modeling, which is extremely hard to do when you’re talking about the climate.” 
US Public Opinion
A Jan. 22, 2019 report from the Yale Program on Climate Change Communication found that 73% of Americans think global warming is occurring, marking a ten percentage point increase over Mar. 2015 meanwhile, 14% of Americans deny climate change is happening. Six in ten surveyed (62%) believe that global warming is being caused by humans, while 23% attribute it to “natural changes in the environment.” 
The group’s 2018 report showed that 95% of liberal Democrats think global warming is happening and 84% think it is caused by humans. On the other end of the ideological spectrum, 40% of Republicans think global warming is happening and 26% think it is caused by humans. 
A 2017 Gallup poll found that 68% of Americans thought global warming was caused by human activity, up from 50% in 2010 and 61% in 2001, while 29% thought it was caused by natural causes, down from 46% in 2010 and 33% in 2001. 
A 2018 Pew Research Center poll found that 18% of Republicans in the Baby Boomer generation thought that “the earth is warming mostly due to human activity,” compared to 36% of millennial Republicans and 75% of all Democrats.  A July/Aug. 2019 Washington Post-Kaiser Family Foundation survey found that 86% of teenagers believe human activity is causing climate change, compared to 79% of adults. 
Learning and Teaching from Climate Change
Integrating climate into history should present historians with more opportunities than obstacles. Even in well-covered fields, such as colonial America, applying new data from climate studies offers researchers a rare chance at conducting cutting-edge research. Previously unknown or unappreciated climate phenomena can supply novel perspectives and explanations for major historical developments, as in recent discussions of the &ldquogeneral crisis of the seventeenth century&rdquo from Western Europe to China. 1
Nor should historians neglect the contributions they can make to climate science. Climate reconstructions benefit from written observations gathered by historians and geographers, and much more remains to be collected. Historians should not be afraid to reach out to colleagues in the climate sciences to discuss how we might use their data more effectively and what we might offer them in return.
Furthermore, with the acceleration of climate change, historians have the chance to chronicle a major world-changing development firsthand. Human-induced global warming is no longer just a theory but an established event, and because no end is in sight to climate change, there seems little point in waiting to write its history.
Even historians uninvolved in climate-related research may consider how to incorporate climate into their classes. Environmental historians have an important role to play, not only in addressing the effects of climate change but also in placing the so-called climate debate in the framework of previous environmental policy and politics. But historians in all fields possess insights and examples from the past valuable to the present.
Public opinion often places an arbitrary distinction between scientific &ldquotheory&rdquo and historical &ldquofact.&rdquo Unfair and inaccurate as that distinction may be, it reminds us that when it comes to climate change, most people are still grasping for a tangible understanding of what otherwise seems a mere abstraction. While history does not offer perfect facts and tidy explanations, it can convey human experiences of a changing climate and extreme events. A good anecdote or narrative can be more enlightening and persuasive than any number of quantitative studies.
From Stockholm to Kyoto: A Brief History of Climate Change
In the midst of the current international debate on global warming, it is instructive to note that it has taken the United Nations and the international community some two generations to reach this point.
To fully understand the current debate, one must look at the rise in prominence of environmental issues on the global agenda and the evolution of climate change within that context. Environmental issues, much less climate change, were not a major concern of the United Nations in the period following the Organization's creation. During its first 23 years, action on these issues was limited to operational activities, mainly through the World Meteorological Organization (WMO), and when attention was paid to them, it was within the context of one of the major preoccupations of that time: the adequacy of known natural resources to provide for the economic development of a large number of UN members or the "underdeveloped countries", as they were then termed.
In 1949, the UN Scientific Conference on the conservation and utilization of resources (Lake Success, New York, 17 August to 6 September) was the first UN body to address the depletion of those resources and their use. The focus, however, was mainly on how to manage them for economic and social development, and not from a conservation perspective. It was not until 1968 that environmental issues received serious attention by any major UN organs. The Economic and Social Council on 29 May was the first to include those issues in its agenda as a specific item and decided -- later endorsed by the General Assembly -- to hold the first United Nations Conference on the Human Environment.
Held in Stockholm, Sweden from 5 to 16 June 1972, the UN Scientific Conference, also known as the First Earth Summit, adopted a declaration that set out principles for the preservation and enhancement of the human environment, and an action plan containing recommendations for international environmental action. In a section on the identification and control of pollutants of broad international significance, the Declaration raised the issue of climate change for the first time, warning Governments to be mindful of activities that could lead to climate change and evaluate the likelihood and magnitude of climatic effects.
The UN Scientific Conference also proposed the establishment of stations to monitor long-term trends in the atmospheric constituents and properties, which might cause meteorological properties, including climatic changes. Those programmes were to be coordinated by WMO to help the world community to better understand the atmosphere and the causes of climatic changes, whether natural or the result of man's activities. The Conference also called for the convening of a second meeting on the environment and established the Governing Council of the United Nations Environment Programme (UNEP), with its secretariat in Nairobi, Kenya, the Environment Fund and the Environment Coordination Board. But climate change did not become a central preoccupation of those bodies. Water resources, marine mammals, renewable energy resources, desertification, forests, environmental legal framework and the issue of environment and development took centre stage.
Over the next 20 years, as part of efforts to implement the 1972 decisions, concern for the atmosphere and global climate slowly gained international attention and action. In 1979, the UNEP Governing Council asked its Executive Director, under the Earth Watch programme, to monitor and evaluate the long-range transport of air pollutants, and the first international instrument on climate -- the Convention on Long-Range Transboundary Air Pollution -- was then adopted. UNEP took it to another level in 1980, when its Governing Council expressed concern at the damage to the ozone layer and recommended measures to limit the production and use of chlorofluorocarbons F-11and F-12. This led to the negotiation and adoption in 1985 of the Vienna Convention for the Protection of the Ozone Layer and the conclusion of a Protocol to the 1979 Transboundary Air Pollution Convention, which aimed at reducing sulphur emissions by 30 per cent. In the meantime, palpable evidence of climate change due to air pollution was beginning to emerge in the phenomena of acid rain in Europe and North America, which resulted in various programmes by UNEP and WMO for keeping it in check.
However, in 1987 the UN General Assembly gave real impetus to environmental issues, when it adopted the Environmental Perspective to the Year 2000 and Beyond -- a framework to guide national action and international cooperation on policies and programmes aimed at achieving environmentally sound development. The Perspective underlined the relationship between environment and development and for the first time introduced the notion of sustainable development. It was disappointing, however, that such a long-term policy document, while recognizing the need for clean air technologies and to control air pollution, did not make climate change a central issue, but subsumed it under its policy directive related to energy.
In 1988, global warming and the depletion of the ozone layer became increasingly prominent in the international public debate and political agenda. UNEP organized an internal seminar in January to identify environmental sectors that might be sensitive to climate change. The Intergovernmental Panel on Climate Change (IPCC), a forum for the examination of greenhouse warming and global climate change, was established and met for the first time in November. The General Assembly identified climate change as a specific and urgent issue. In its resolution on the protection of global climate for present and future generations of mankind, it asked WMO and UNEP to initiate a comprehensive review and make recommendations on climate change, including possible response strategies to delay, limit or mitigate the impact of climate change. As a result, 1989 was a watershed year for climate change, as the first significant global efforts were taken. The Assembly, in resolution 44/207, endorsed the UNEP Governing Council's request to begin preparations with WMO for negotiations on a framework convention on climate change regional action was also being taken. In addition, the Maldives transmitted the text of the Malé Declaration on Global Warming and Sea Level Rise to the UN Secretary-General and the Helsinki Declaration on the Protection of the Ozone Layer was adopted on 2 May. Also in 1989, the Montreal Protocol on Substances that Deplete the Ozone Layer entered into force.
Efforts to raise awareness of the effects of climate changes were further advanced at the second World Climate Conference, held from 29 October to 7 November 1990. In its Ministerial Declaration, the Conference stated that climate change was a global problem of unique character for which a global response was required. It called for negotiations to begin on a framework convention without further delay. As the urgency for a stronger international action on the environment, including climate change, gained momentum, the General Assembly decided to convene in 1992 in Rio de Janeiro, Brazil, the United Nations Conference on Environment and Development. The Earth Summit, as it is also known, set a new framework for seeking international agreements to protect the integrity of the global environment in its Rio Declaration and Agenda 21, which reflected a global consensus on development and environmental cooperation. Chapter 9 of Agenda 21 dealt with the protection of the atmosphere, establishing the link between science, sustainable development, energy development and consumption, transportation, industrial development, stratospheric ozone depletion and transboundary atmospheric pollution.aThe most significant event during the Conference was the opening for signature of the United Nations Framework Convention on Climate Change (UNFCCC) by the end of 1992, 158 States had signed it. As the most important international action thus far on climate change, the Convention was to stabilize atmospheric concentrations of "greenhouse gases" at a level that would prevent dangerous anthropogenic interference with the climate system. It entered into force in 1994, and in March 1995, the first Conference of the Parties to the Convention adopted the Berlin Mandate, launching talks on a protocol or other legal instrument containing stronger commitments for developed countries and those in transition.
The cornerstone of the climate change action was, therefore, the adoption in Japan in December 1997 of the Kyoto Protocol to the UNFCCC, the most influential climate change action so far taken. It aimed to reduce the industrialized countries' overall emissions of carbon dioxide and other greenhouse gases by at least 5 per cent below the 1990 levels in the commitment period of 2008 to 2012. The Protocol, which opened for signature in March 1998, came into force on 16 February 2005, seven years after it was negotiated by over 160 nations.
Once again, the United Nations has shown its leadership role in bringing issues requiring global action to international attention. However, its efforts throughout the years to make the issue of climate change a central focus of the international agenda continues, even as opposing sides of the debate try to make their case. As evidence of the risks of ignoring climate change become more striking, the United Nations will persevere in that effort until the issue is embraced by all.
Harbingers of doom: a brief history of climate change warnings
Understanding the root cause of climate change took many decades of painstaking research. Here, as a major United Nations-sponsored climate change summit begins in Katowice, Poland, Paul Parsons traces the story of how science foretold hell and high water.
This competition is now closed
Published: December 3, 2018 at 11:31 am
Sandbags, severe flood warnings, mass evacuations – desperate measures as a three-metre-high wall of water bears down on a densely populated coastline. This isn’t fiction. Nor is it an account of tragic events far away in the Indian Ocean. This happened in November 2007 in England, when a huge storm surge welled in the North Sea then smashed into the country’s east coast.
On this occasion sea defences held fast and no one was injured. But a similar incident in 1953 left over 300 people dead. Climatologists now warn that extreme weather events such as this are set to get ever more common, as we start to feel the effects of global climate change.
There are other signs too. According to NASA, 2005 was the warmest year we’ve seen since records began. Malaria has been reported in Nairobi, Kenya as the city’s high altitude becomes warm enough for mosquitoes carrying the disease to survive there.
“There’s no question that we are seeing the effects of climate change already,” says Spencer Weart, director of the Center for History of Physics, at the American Institute of Physics, Maryland.
In February 2007, the Inter-governmental Panel on Climate Change (IPCC) published an Assessment Report that concluded that the world will see a probable temperature rise of between 1.8 and 4 degrees Celsius by the end of the century. “We know the last time the world was three degrees warmer for any long period of time, the sea level was six metres higher,” says Weart. That’s enough to submerge coastal cities from New York to Shanghai.
Piecing together the scientific evidence for climate change has been a long and difficult process. It has occupied thousands of bright minds for more than a century – and has been fraught with controversy and political intrigue.
The story began with the discovery, by French scientist Joseph Fourier, of what we now call the ‘greenhouse effect’. In 1824, Fourier calculated that the Earth was a lot warmer than it should be according to estimates based purely on its distance from the Sun. He surmised that the planet’s atmosphere must be slowing down the rate that the planet radiates heat away into space. Light from the Sun passes through the atmosphere to warm the land and oceans below, but the atmosphere prevents this heat escaping – just like the glass in a greenhouse.
In 1896, a Swedish chemist took the theory further. Svante Arrhenius noticed that the gas carbon dioxide (CO2) was especially good at trapping heat radiation. He soon realised what this meant: that the massive increases in atmospheric CO2, caused by coal burning during the industrial revolution, would fuel Fourier’s greenhouse effect and lead to global warming of the planet.
Far from triggering wide-scale panic, Arrhenius’s prediction was actually welcomed. During the late 19th century geologists had turned up evidence for what they perceived as a far greater climate menace. They discovered that the Earth’s prehistory had been punctuated by long periods of glaciation – when the planet’s surface froze over for hundreds of thousands of years at a time. Arrhenius had actually been investigating the greenhouse effect as a possible explanation of these ‘Ice Ages’. Instead, he stumbled upon a mechanism whereby human CO2 emissions could save us from a frosty fate. And it wasn’t the only benefit. Global warming could be advantageous to food production, bringing marginal lands into cultivation. “Vast land areas in the northern hemisphere could become good agricultural land if the weather warmed,” says Jack Meadows, a science historian at the University of Loughborough. “Canada and the eastern part of Russia was very much a wheat area then, but limited by the short growing season.”
But this was all still theoretical – hard evidence for the changing climate had yet to be seen. It’s true that, in the 15th century, Christopher Columbus had reported that there was less rainfall in the Canary Islands as the inhabitants cut the forest down. During the 17th and 18th centuries, northern Europe experienced an era of extreme cold when the River Thames would regularly freeze – known as the Little Ice Age.
These were regional effects though. It wasn’t until later that the signs of climate change on a global scale began to surface. “In the 1930s older people began to say, ‘you kids have it easy – when I went to school there were blizzards, or the rivers froze,’” says Weart.
A British scientist by the name of Guy Callendar first gathered numerical data to support the anecdotes. In 1938, he published figures showing that between 1890 and 1935, the Earth had warmed by about half a degree Celsius. He pointed out that carbon dioxide levels had risen by ten per cent in this time, owing to the industrial revolution. It was the first solid scientific observation linking climate warming with human carbon emissions.
But nobody believed it. By this time, other research had suggested that the Earth’s oceans absorb excess carbon dioxide, and thus act as a natural brake on the greenhouse effect. At any rate, even Callendar believed that the warming effect would still be largely beneficial.
It wasn’t until 1957 that this thinking was overturned. Roger Revelle, at Scripps Institute of Oceanography in California, with his colleague Hans Seuss, showed that as an ocean absorbs CO2 it becomes more acidic. This radically limits the amount of carbon it can soak up.
Fears become fact
Revelle also reasoned that human CO2 emissions must now be increasing exponentially. For not only was the world’s population doubling every few decades, but the carbon output per capita was itself doubling on the same timescale. His fears became fact just a year later, when Charles David Keeling, also at Scripps, began a careful programme of CO2 monitoring. He found the concentration of the gas to be 315 parts per million, compared with 280ppm in the pre-industrial 19th century. Continuing his measurements until 1961, Keeling charted an inexorable year-on-year rise.
The prevailing attitude of the time was to equate – without question – all human industry with progress. The work of Revelle and Keeling shook this philosophy. But the real body blow came from another quarter entirely: nuclear weapons. “People thought that bomb tests were causing earthquakes and droughts and floods. Fall-out was going around the world,” says Weart. “So human industry is not necessarily all progressive, and human beings can change the entire global environment.”
This awareness – along with concerns over issues such as pollution and chemical pesticides – sparked the first glimmers of the environmental movement. Climate change now had a public voice. Scientists started to listen, and carried out research into its consequences. “By the late 1960s, you began to find scientists warning that global warming may very well be a danger,” says Weart.
So began a long and intense phase of climate research. The number of scientific papers published on the subject leapt from two or three a year to between 20 and 30. By 1977, there was a chorus of scientists calling for policy steps to curb carbon emissions. Otherwise, they warned, the world was going to get dramatically warmer in the 21st century, with potentially catastrophic results.
Controversy was also brewing though. The new research revealed just what an intricate system the climate really is – dependent on many, many variables, with no single ‘master key’ to unlock its behaviour. This led some scientists to doubt that human activity was the root cause of global warming. These ‘climate sceptics’ blamed natural factors, such as variations in the brightness of the Sun.
Nevertheless, the evidence for anthropogenic global warming continued to accumulate. Scientists found that it wasn’t just carbon dioxide that causes global warming, but also other gases given off by human activity, such as methane and nitrous oxide – a greenhouse gas 300 times more potent than CO2. Chlorofluorocarbons (CFCs) made headlines. Used widely as refrigerator coolants and aerosol propellants (although now banned), they were up to 8,000 times as harmful as CO2. Worse still came the news that CFCs were ripping a hole in the Earth’s ozone layer – a protective blanket in the upper atmosphere that blocks harmful rays from the Sun.
The news enraged environmentalists, who stepped up their campaigning. In response, climate sceptics defended their position even more aggressively. The debate became a highly polarised, and sometimes even irrational stand-off.
There was only one way to break the stalemate: more cold, hard scientific research. “Over the last 20 years, the international scientific community has been carrying out research on many, many facets of the climate system,” says Alan Thorpe, chief executive of the UK’s Natural Environment Research Council. “Determining the cause of climate change has required improved understanding of many environmental factors, as well as improvements in our ability to model the climate system.”
That’s been achieved through massive advances in computer modelling. Increases in computing power have enabled basic models of the atmosphere, first formulated in the 1980s, to become vastly more realistic. They now accurately reflect the climate’s impact on land masses, oceans and ice sheets. The treatment of physical processes, such as atmospheric chemistry, has been greatly refined.
The results of this modelling have now all but ruled out natural processes as the chief cause of climate change. One study carried out last year by Mike Lockwood, of Rutherford Appleton Laboratories, near Oxford, examined the last 20 years’ worth of solar variations – one of the major factors cited by climate sceptics. Lockwood found that if the Sun was the main contributor to climate change then the planet should actually be getting cooler – in clear contradiction of the evidence. Consequently, the IPCC stated in its 2007 Assessment Report that the likelihood of global warming since the mid-20th century being caused mainly by human greenhouse gas emissions is now in excess of 90 per cent.
In 2006, the Stern Review of the economic impact of climate change was published. It found that the dollar cost of inactivity – and so suffering the consequences of global warming – grossly outweighed the cost of taking early action to stop it. Meanwhile, military commanders warned of the potential threat to national security posed by mass migrations of refugees from flood lands, and by conflicts over resources as starving nations went to war for food.
These strands came together to build a compelling case for governments to act. The Kyoto Protocol, capping carbon emissions, has now been ratified by 182 signatories – the notable exception being the United States. In 2009, world representatives are due to meet for talks in Copenhagen to finalise the terms of a new treaty that will replace Kyoto once it expires in 2012.
There’s still much to be done to avert environmental hell and high water. But understanding the science of global climate change could literally have saved the world. And it has achieved something else equally incredible – teaching national leaders to look beyond both their borders and short electoral terms. That’s got to be a good thing.
Dr Paul Parsons was formerly editor of award-winning science and technology magazine Focus. His latest book, The Science of Doctor Who, was long-listed for the 2007 Royal Society Prize for Science Books.
Timeline: The weathermen
French scientist Jean Baptiste Joseph Fourier (1768–1830) predicts the greenhouse effect – in which the Earth’s atmosphere traps heat and makes the planet warmer than it otherwise would be.
The French polymath is best known for the ‘Fourier series’ – a tool for breaking down complex mathematics into simpler forms – useful in physics, such as heat flow and wave theory, and in communications. It was Fourier who discovered the ‘greenhouse effect’.
Swedish chemist Svante Arrhenius (1859–1927) calculates that industrial carbon dioxide emissions will enhance the greenhouse effect, leading to global warming. He didn’t know it had already begun.
This Swedish chemist was first to realise that human emissions of carbon dioxide could aggravate the greenhouse effect. Arrhenius was also an early proponent of ‘panspermia’ – the theory (now taken very seriously) that spores of life can drift between the planets.
The first evidence for global warming is brought to light by British researcher Guy Stewart Callendar (1898–1964). He links rising temperatures with increasing carbon dioxide levels since 1850.
A steam engineer by profession, Callendar became intrigued by the impact of steam power, and other products of the industrial age, upon the environment. He was first to tally soaring temperatures since the mid-19th century with increasing carbon dioxide levels.
Roger Revelle in the USA calculates that much less CO2 is absorbed by the Earth’s oceans than originally thought, leaving a great deal to warm the planet.
Charles David Keeling (1928–2005) begins careful measurements of atmospheric CO2 levels at Mauna Loa Observatory in Hawaii. In 1961 he publishes evidence for a relentless year-on-year rise.
Geochemist and oceanographer Keeling extended Callendar’s work into the modern age, charting the ongoing rise in atmospheric CO2. His graph became known as the ‘Keeling curve’. In 2002, he received the US National Medal of Science for his climate research.
The first reliable computerised climate simulation yields grim predictions – doubling of carbon dioxide levels from pre-industrial times will raise the Earth’s temperature by 2.3 degrees Celsius.
American climatologists Michael Mann (1965–), Raymond Bradley and Malcolm Hughes publish the ‘hockey stick’ graph, showing a sharp upturn in global temperatures since the industrial revolution.
Mann led a team who put forward the ‘hockey stick’ graph. A key piece of evidence for anthropogenic global warming, it plotted northern hemisphere temperatures over the last 1,000 years, showing a sharp rise at the start of the 20th century.
The Intergovernmental Panel on Climate Change reports that the likelihood of human carbon dioxide emissions being responsible for most observed climate warming is now over 90 per cent.
Why didn’t we listen?
For decades, the atomic bomb put climate change in the shade
Global warming was initially seen as a good thing – it could stave off the next Ice Age, and open up more land for food production. That changed dramatically when the first computer simulations of the 21st-century climate threw up grim prognostications of soaring temperatures and rising sea levels. That was back in 1967. Why has it taken so long for the world to heed the warnings?
Firstly, the year 2000 seemed a long way away. Those who had lived through the first half of the 20th century had seen terrific short-term upheavals, including two world wars and economic catastrophe. By the Sixties, other very immediate threats to the planet had emerged – such as the Cold War and the atomic bomb.
“It would be hard to expect anybody to take action until they saw changes on a timescale that was meaningful to them,” says Spencer Weart, director of the Center for History of Physics, at the American Institute of Physics, Maryland. “It was hard to imagine planning even two years ahead.” Scientists were listening, though. Come the 1970s, many were devoting serious research effort to climate change. The problem was that convincing governments to change tack on any scientific issue required scientific consensus. Yet the climate is complex – understanding it to the point where consensus could be reached was to take many years of research.
By the end of the 1990s most agreed it was more likely than not humans were to blame. At the same time, the end of the Cold War and increased international stability allowed environmental issues to rise up the public agenda. “People were now willing to plan 50 years ahead,” says Weart.
Under pressure from their electorates to take action, and with scientific evidence mounting, policy makers had little choice but to make fighting climate change a priority.
12 Important Moments in the History of Climate Action: In Photos
Young climate activists involved in the #FridaysForFuture movement have been determined not to allow the worldwide coronavirus lockdowns curb their momentum.
The weekly school strikes sparked by Greta Thunberg to inspire action on the climate crisis have moved online — thousands have been involved in virtual events, and in raising awareness about climate change on social media using the #climatestrikeonline hashtag.
But climate activism didn't suddenly appear — although recent years have seen a huge breakthrough in capturing the attention of the world, the digital effort during the pandemic is just the latest innovation in a movement that has evolved over decades.
From the first utterance of the term "global warming" to environmental activism spilling out onto streets around the world, we've flicked through the history books to learn a bit more about the climate movement's past. Here's a brief look at some of the key moments that have brought us to where we are today.
1. The birth of 'global warming'
In 1965, scientists on the US President’s Science Advisory Committee first put forward concerns about a “greenhouse effect”.
In a report called "Restoring the Quality of Our Environment", the scientists proposed that increasing temperatures in the atmosphere was caused by a buildup of carbon dioxide. But it wasn’t until 1975 that the term “global warming” was coined by geoscientist Wallace Broecker — and it took years before the issue reached mainstream understanding.
Judy Moody works in a poster-filled office of the Environment Teach-In, Inc., in Washington, April 9, 1970. The organization is coordinating school activities for the nationwide observance of Earth Day on April 22. Image: Charles W. Harrity/AP
The first-ever Earth Day was held in the US almost exactly 50 years ago on April 22, 1970.
The organisers wanted to raise awareness of concerns such as pollution and toxic waste and were inspired by the anti-war movement led by students at the time, according to its website. Earth Day has now become a global event ever since 1990, when 200 million people in 141 countries joined forces to bring it to the world stage.
By the late 1980s, droughts and record heat led to media coverage around the world, with the LA Times, for example, reporting in 1989 on British scientists' discovery that the previous year had been the hottest ever on record — and crucially, linked this rising heat level to "global warming."
The story was pertinent in California as the same year the California Energy Comission predicted that the droughts, heatwaves, and wildfires they had experienced were likely to hit the state with more frequency in the years to come.
New Melones Lake, California during a 2015 drought. The increased frequency of droughts and heatwaves had been predicted in 1989 by the California Energy Commission. Image: Ben Amstutz, Flickr
4. The IPCC
In 1988, the UN launched its Intergovernmental Panel on Climate Change (IPCC). The expert panel was given the job of assessing the developing science on climate change and providing up-to-date information to governments. Importantly, the IPPC's reports are used as a reference point in international climate negotiations — a key part of the process of getting countries to agree the necessary steps to tacke the issue.
The launch of the IPCC was a big step towards getting countries to attempt to cooperate on how they dealt with the threat of global warming — and decades later in October 2018, it was the IPCC that reported the world only had 12 years left to limit climate catastrophe before its consequences became irreversible.
5. The Rio Earth Summit
The Rio Earth Summit — an international conference on sustainable development held by the UN in 1992 — established a set of principles for improving and protecting the environment adopted by 178 countries.
It was the first time that the issues of economy, climate, and international development were considered together, but the summit was not revisited for another 20 years — when Rio+20 was held in June 2012.
Tucano, an indigenous group from the Amazon rainforest, dance at the opening ceremony of a world conference of native peoples, a week before the Earth Summit in Rio De Janeiro, Brazil, May 26, 1992.
Image: Altamiro Nunes/AP
6. The Kyoto Protocol
In 1997, developed nations gathered in Kyoto, Japan, to agree on a historic climate plan — it was the first agreement between nations to mandate the reduction of greenhouse gases.
The international treaty was called the Kyoto Protocol: a pledge for industrially-advanced countries to reduce emissions by an average of 5% by the period 2008-12, although there were wide variations on targets for individual countries. The US Senate immediately declared it would not ratify the treaty.
In the 2000s, large-scale demonstrations calling for action on climate change became regular events.
Between 2000 and 2019, nine of the hottest years ever recorded took place, but fossil fuel consumption was still rising ever higher. It led to the founding of international pressure groups, such as 350.org — an organisation founded to build a global climate movement.
In 2005, the first Global Day of Action took place during the UN climate talks in Montreal — with people taking part in Canada and around the world, from Bangladesh to Australia. The demonstrations have continued every year.
Some of thousands of people demonstrating on the the street in central Copenhagen, Denmark, Dec. 12, 2009.
Image: Jens Dresling/Polfoto/AP
8. Student pressure
In 2011, student groups in the US and later the UK and around the world began pressuring universities to divest from fossil fuels. It was the birth of an effective new focus for campaigners, and students slowly began to see some success.
By 2014, 837 institutions and individual investors had committed to divestment, although only 13 of these were US-based. That same year, the University of Glasgow became the first British university to divest.
A global movement, fronted by the non-profit network Fossil Free, signed up groups all over the world to pressure companies and institutions to divest, and by the end of 2019 had secured $11 trillion in divestment from fossil fuels. The movement continued to blossom and by the start of 2020, half of the UK’s 154 universities, for example, had committed to divestment from fossil fuels.
9. Rising sea levels
Pacific Islanders began to sound the alarm as rising sea levels threatened land and livelihoods. In 2014, their activism became more direct, as a group a known as the Pacific Climate Warriors from the Marshall Islands, Fiji, Vanuatu, Tokelau, and the Solomon Islands joined a flotilla blocking boats using the Newcastle coal port in Australia — to highlight the role of Australian coal exports in warming the planet and impacting their lives
Ahead of launching the boats, Koreti Tiomalu, an outreach coordinator for the activists, told 350.org why they were doing it: “For over 20 years Pacific Islanders have been negotiating with little effect with countries like Australia to cut their greenhouse gas emissions. This is a way for the warriors to stand up and say they are not drowning, they are fighting.”
A group of Pacific Climate Warriors in 2014. (Image: 350.0rg/Flickr).
During the 2010s, public performance art on climate change became a symbol of protest.
From giant hands pulling down buildings at the 2017 Venice Biennale, to ice sculptures melting outside London’s Tate Modern in 2018, art was fueling climate activism everywhere.
11. Direct action
Extinction Rebellion, a direct action group that organises creative forms of protest, launched in London in May 2018.
The group brought the UK capital to a standstill and began targeting events such as Fashion Week in order to further their mission. Chapters of the group have since opened in 68 countries around the world, from Russia to South Africa.
A young Extinction Rebellion climate change protester holds a banner as they briefly block a road in central London, Wednesday, April 24, 2019.
Image: Matt Dunham/AP
12. Greta Thunberg
In August 2018, then 15-year-old Greta Thunberg went on her first school strike, sitting alone outside the Swedish parliament to protest inaction on the climate crisis.
Thunberg urged leaders to take climate action seriously if they wanted children to study for their future. Her action sparked a global movement led by school students regularly striking on Fridays under the banner "Fridays for Future", while Thunberg went on to be nominated for a Nobel Peace Prize after her viral speeches to politicians around the world.
Swedish climate activist Greta Thunberg, center, lifts her sign which reads 'school strike for the climate' as she attends the 'Friday For Future' rally in Berlin, Germany on March 29, 2019.
Image: Markus Schreiber/AP
Now, in 2020, the climate movement has become global and digital. Studies throughout 2019 have shown that the climate crisis is moving up the agenda for voters in countries around the world — in some cases, like in the UK, making it into the top five issues facing the nation that the electorate cared about.
Greta Thunberg has been joined by the likes of Vanessa Nakate in Uganda, Aditya Mukarji in India, Alexandria Villaseñor in the US, and tens of thousands of others. These activists will continue to inspire political change and make their own history for years to come.
Join the movement by taking action here to help protect the environment, and mitigate the impacts of climate change on the world's most vulnerable people.