32 The History of Climate Change
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Introduction to Climate Change Before the Modern Era
Climate change refers to long-term alterations in Earth’s temperature, precipitation patterns, and atmospheric conditions. While it is commonly discussed in the context of modern global warming, the science of climate change has roots that stretch back nearly two centuries. Understanding the past of climate change, including both Earth’s natural fluctuations and the rise of human influence, is crucial for making sense of the present crisis and shaping future responses. (ME)
Historically, Earth’s climate has changed due to natural factors such as shifts in the planet’s orbit, volcanic activity, and solar variability. These processes caused ice ages and warmer interglacial periods, long before humans had any measurable impact. However, as early as the 19th century, scientists began to investigate how human activities might alter Earth’s climate. In 1896, Swedish scientist Svante Arrhenius proposed that emissions of carbon dioxide (CO₂) from coal burning could warm the planet, a groundbreaking idea that laid the foundation for modern climate science (Le Treut & Somerville, 2007). (ME)
Over time, scientific discoveries, and data collection. such as the Keeling Curve, which began tracking atmospheric CO₂ in 1958, confirmed that greenhouse gas concentrations were increasing rapidly due to industrial activity (Le Treut & Somerville, 2007). By the late 20th century, public and political awareness began to catch up with scientific concern. In 1988, NASA climatologist James Hansen testified before the U.S. Senate that global warming was no longer a theoretical issue, it was observable and underway (History.com Editors, 2017). That same year, the Intergovernmental Panel on Climate Change (IPCC) was established to assess scientific evidence and inform global policy. (ME)
This chapter explores the evolution of climate change from Earth’s natural climatic shifts to the rise of industrial emissions and early scientific warnings, culminating in the political recognition of climate change by 1989. Understanding this history is essential, not only to appreciate how far climate science has come, but also to recognize the delay between discovery and action. The past of climate change reveals a long journey of observation, debate, and realization. a journey that continues to shape our present and our future. (ME)
Natural Climate Change Before Human Influence
Long before humans started changing the atmosphere, Earth’s climate changed very slowly over thousands or even millions of years, driven by powerful natural forces. These included gentle shifts in the Earth’s orbit, volcanic eruptions, changes in the Sun’s energy output, and the movement of the oceans. While these processes sometimes led to major environmental events, like the ice ages, they happened gradually and in cycles. This slow pace gave plants, animals, and ecosystems a chance to adapt over time. Recognizing how these natural factors worked helps us understand how modern climate change is different from Earth’s usual patterns. (ME)
One of the biggest natural influences is a set of long-term astronomical cycles called Milankovitch cycles. These are slow changes in Earth’s shape and tilt, alterations in the orbit, the tilt of the axis, and the wobble of Earth, that affect how much sunlight reaches various parts of the planet. Over tens of thousands of years, these cycles have caused periods of deep ice and times when the climate was warmer. For example, about 20,000 years ago, the Earth was at the peak of the last Ice Age, with huge ice sheets covering much of North America and Europe. These cycles are predictable and have been a key part of Earth’s climate system for over two million years (Graham, 2000). (ME)
Volcanoes also play a big role in cooling the planet from time to time. When a volcano erupts, it can send substantial amounts of sulfur dioxide and ash high into the atmosphere. These particles reflect sunlight away, which can temporarily lower the global temperature. A well-known example is the eruption of Mount Tambora in 1815, this caused what is called the “Year Without a Summer,” when many regions faced crop failures, famines, and strange weather patterns (History.com Editors, 2017). While eruptions can cause short-term climate change, long-lasting effects usually require multiple big eruptions over an extended period. (ME)
Solar activity also impacts Earth’s climate. The Sun’s energy output changes slightly over roughly 11-year cycles. When solar activity dips, like during the Maunder Minimum between 1645 and 1715, global temperatures tend to be cooler. That period coincided with part of the Little Ice Age, a time when winters were longer and colder, and growing seasons shrank in parts of Europe and North America (What Is Paleoclimatology?, 2016). Today, satellites show that solar activity has not increased much recently, which suggests that modern global warming is not caused by changes in the Sun’s energy alone. (ME)
Another major driver of past climate change is ocean circulation. Ocean currents disperse heat around the globe and affect local climates. When these currents move, even slightly, they can have large-scale impacts. For instance, the Atlantic Ocean’s circulation system, also referred to as the “global conveyor belt,” carries warm water from the tropics to the north. Changes in this system in the past have led to sudden cooling events, especially during the Ice Age (What Is Paleoclimatology?, 2016). The ocean stores and moves enormously more heat than the atmosphere, and as such is a key player in Earth’s climate system. (ME)
We learn about these natural changes through paleoclimate science, the study of past climates using natural evidence. Scientists derive data from documents like tree rings, sediment layers, and ice cores. Some of the most significant examples include ice core data in Antarctica, especially from the Vostok station. Such long ice cylinders contain tiny bubbles of ancient air, which give scientists tools to measure levels of greenhouse gases like carbon dioxide in the past. The Vostok ice core shows that over the past 800,000 years, carbon dioxide never rose more than 300 parts per million, until recent history. Today, concentrations of carbon dioxide have gone well over 420 parts per million, far exceeding anything in natural history (What Is Paleoclimatology?, 2016). (ME)
Figure 1. Atmospheric carbon dioxide concentrations over the past 800,000 years, derived from Antarctic ice core data. The graph shows natural fluctuations in CO₂ levels between approximately 180 and 280 parts per million (ppm) during glacial and interglacial periods. In recent times, CO₂ concentrations have risen sharply, surpassing 400 ppm, a level unprecedented in the ice core record. (ME)
These natural histories show a world where climate did shift, but at a very much slower rate than what we are seeing today. The warming today is happening over decades, not millennia, and is not caused by orbital cycles or volcanic activity. Instead, it is linked to something entirely new: human activity. But even before industrial smokestacks and gas-burning engines, humans were beginning to affect the Earth’s atmosphere in quieter, less obvious ways. In the next section, we will find that early agricultural communities, through deforestation, livestock grazing, and other land use changes, initiated the first chapter of human intervention in the world climate. (ME)
Early Human Impact (Pre-Industrial Era)
Whereas the climate of the Earth was naturally formed for millions of years, human societies had silently but quantitatively started their influence far before the onset of industrialization. Even though a lot smaller in scale compared to current fossil fuel consumption, these processes in ancient times cumulatively over a period of centuries contributed new processes to the Earth’s atmosphere. In particular, agricultural expansion, deforestation, pastoralism, and land-use change provided bases for long-term environmental change. (ME)
The evolution of agriculture around 10,000 years ago, or the Agricultural Revolution, led to tremendous environmental transformation. When human populations grew and settled in fixed locations, forests were cleared to provide space for fields and pastures. Deforestation released stored carbon in trees and soil into the air as carbon dioxide (CO₂). Although populations were low initially, the progressive spread of agriculture over continents contributed to continuously increasing greenhouse gas levels over a long time (NASA, 2024b). (ME)
Rice agriculture spread was one of the major producers of greenhouse gases during pre-industrial times. In particular, flooded rice paddies ensured ideal conditions for methane-producing microbes to multiply. Methane (CH₄) is a very potent greenhouse gas, and the widespread spread of rice cultivation in some parts of Asia introduced a new source of atmospheric warming. Similarly, animal domestication, such as cows, sheep, and goats, also contributed to rising methane emissions from digestive processes. These animals were not only a source of food but an indirect cause of early climate change (NASA, 2024b). (ME)
The use of fire as a means to clear land and farms also came into use. Slash-and-burn methods were used by ancient societies to plant land, releasing additional CO₂ and black carbon (soot) into the atmosphere. Both ancient civilizations and Indigenous people all over the globe used such methods. Such emissions were insignificant relative to contemporary use of fossil fuels but were geographically extensive and long-term. (ME)
Modern scientific restoration shows that these human activities may have sustained higher atmospheric CO₂ and methane levels than they otherwise would have by natural conditions alone. For instance, according to some scientists, greenhouse gas levels during the last 8,000 years should have fallen in accordance with natural climate patterns but instead changed relatively little or even rose, due to initial agriculture and forest clearance (Graham, 2000). These small increases in greenhouse gases may have delayed the onset of a new ice age, stealthily influencing long-term climate patterns. (ME)
These shifts developed over millennia and were not yet strong enough to cause rapid global warming. They do, however, represent the start of what would later become a much larger trend: human modification of the Earth’s climate system. Unlike natural processes such as volcanic eruptions or orbital changes, early human activity was persistent and cumulative, slowly altering the atmospheric composition over centuries. (ME)
Even though pre-industrial societies lacked the machines of the industrial era, their impact on the natural environment was significant. By clearing forests, modifying wetlands, and turning land over to agriculture, they began to change the greenhouse balance of the climate. These pre-industrial changes laid the groundwork for a new kind of climate system; one increasingly controlled by human choice. (ME)
As human communities grew in size and complexity, so did their ability to change the environment. The Industrial Revolution would be the source of the next major rise in climate impact, when the burning of coal, oil, and natural gas fundamentally accelerated the release of greenhouse gases. In the next section, we examine how the consumption of fossil fuels essentially changed the climate of the planet and began the modern era of global warming. (ME)
Industrial Revolution and the Rise of Fossil Fuels
The Industrial Revolution was a revolutionary shift in human history, not just economically and socially, but ecologically. Starting in the late 18th century in Britain and spreading throughout Europe, North America, and ultimately the world, this period brought with it machines fueled by coal, oil, and eventually natural gas. For the first time, fossil fuel energy was used on a large scale, allowing mass production, transportation, and urbanization. This revolution revamped the Earth’s atmosphere and climate radically and in ways that still impact today. (ME)
Before the Industrial Revolution, human carbon dioxide and methane emissions were relatively small and spread out over long times. But industrialization came with an enormously sudden and powerful source of greenhouse gases: fossil fuel burning. Coal became the leading fuel to power factories, locomotives, and steamships. Coal combustion releases carbon dioxide, a potent long-lived greenhouse gas. into the air, where it accumulates and insulates close to the surface of the Earth (NASA, 2024b). (ME)
As additional countries employed coal-based technologies, emissions increased increasingly. In the 19th century, cities and industries expanded rapidly. Forests were harvested not only for agriculture but also for mining, railway building, and expanding urban growth. This resulted in even higher carbon release from soils and vegetation. By the late 1800s, oil and natural gas entered the picture, continuing to drive the level of greenhouse gas emissions associated with industrial activities (Environmental Protection Agency, 2025). (ME)
One of the first signs that the Industrial Revolution was having an international climate impact arrived through a changing atmospheric mix. Although serious attention to human-induced climate change in the 1800s did not materialize, scientists already had thoughts of linking a relationship. Before too long a stretch into the 20th century, though, atmospheric gauging of carbon dioxide began to confirm something theory had already guessed: it was rising at a faster pace than ever before. (ME)
The advent of direct measurement of carbon dioxide in 1958, the Keeling Curve, gave the strongest visual evidence for this trend. Although barely postdating the time covered by this section, it extended what had been built up over a century earlier. In the industrial age, humans had begun to change the atmosphere’s chemistry at a rate and magnitude far larger than natural mechanisms. (ME)
In addition to emitting carbon dioxide, industrialization resulted in blanket air pollution, city smog, and acid rain. They were all eye-catching and real-time in a majority of urban centers, most notably in Britain’s coal-habitable cities and the northeasterly United States. But the long-term, unseeable stockpiling of greenhouse gases led to even more dramatic consequences, continuously raising world average temperatures and initiating changes to weather patterns, sea levels, and ecosystem status. (ME)
The use of fossil fuel became entrenched in the systems of power, transport, and industry worldwide. Energy consumption became a key indicator to gauge national development, and fossil fuel consumption was employed as a measure of progress. As a result, emissions continued to rise throughout the 19th and 20th centuries. By 1900, carbon dioxide in the atmosphere had already exceeded pre-industrial concentrations, and by 1980 had increased by nearly a third. These alterations occurred much more rapidly than anything previously experienced in natural history for the past 800,000 years. (ME)
Figure 2. Cumulative global carbon dioxide emissions from fossil fuels between 1750 and 2000. This graph demonstrates the gradual increase in emissions during the initial stages of industrialization, with a notable acceleration in the 20th century as fossil fuel consumption expanded globally. (ME)
As fossil fuels revolutionized the productivity and patterns of human societies, however, they stabilized the world onto a path of rising emissions and climate disruption. The Industrial Revolution laid the grounds for most of the environmental tragedies the world has today. Here, climate change would now be controlled no more by Earth’s natural cycles but by the preferences and activities of human societies. (ME)
As industrial emissions grew, scientists embarked on identifying the possible consequences of an altered atmosphere. The next section will explain the rise of climate science, how scientists first appreciated the connection between the greenhouse gases and the warming of the world, and how scientific understanding gradually filtered into politics and popular consciousness. (ME)
Scientific Discovery of Climate Change
The science of climate change was not overnight; it was developed over two centuries as scientists labored to grasp the forces that were shaping Earth’s atmosphere. Scientists have constructed a body of evidence linking rising levels of greenhouse gases to global warming, from early investigations of how heat moves through the air to satellite imagery and climate models today. This chapter takes that route, highlighting how our understanding of the greenhouse effect grew, and warnings were sounded decades earlier than climate change came onto the mainstream agenda. (ME)
The roots of climate science date back to the early 1800s. In the 1820s, French scientist Joseph Fourier explored how Earth maintains its temperature. He theorized that while sunlight enters the atmosphere and warms the planet, some of that heat is retained rather than escaping back into space. Though he did not use the term “greenhouse effect,” Fourier’s ideas introduced the concept that Earth’s atmosphere plays a role in trapping heat (NASA, 2024b). (ME)
A few decades later, in 1859, John Tyndall, a British physicist, showed experimental proof that indicated that certain gases in the atmosphere, including carbon dioxide and water vapor, absorb and trap heat. These gases, he found, allow sunlight through but trap infrared radiation, heating the planet. This discovery showed that the atmosphere’s composition could directly affect Earth’s temperature. (ME)
Then in 1896, Swedish scientist Svante Arrhenius took the next big step by proposing that burning fossil fuels could lead to long-term global warming. In fact, he even estimated how much global temperatures would rise if atmospheric carbon dioxide levels were doubled and connected this to the rapidly increasing expansion of coal combustion already being driven by the Industrial Revolution. Although his estimates were based on limited data, his theory helped link human activity to large-scale climatic change. (ME)
In the first part of the 20th century, scientists began observing warming trends in weather records. By the 1930s, some climatologists had already reported that average temperatures were increasing over most parts of the world. The melting of glaciers was also being documented, particularly in Europe and North America. But these changes were not yet identified as part of a global pattern. Some scientists believed that it might be a temporary fluctuation caused by natural variability or solar cycles. (ME)
The pace of scientific progress accelerated in the mid-20th century. A landmark was passed in 1958 when scientist Charles David Keeling began measuring atmospheric carbon dioxide at the Mauna Loa Observatory in Hawaii. These measurements found that CO₂ was not just rising, but it was doing so in a regular and predictable way each year. The graph thereby created, now known as the Keeling Curve, revealed one of the clearest indications that human activities were altering the composition of the atmosphere. This data provided a direct link between the combustion of fossil fuels and atmospheric alteration. (ME)
Figure 3. Monthly average atmospheric CO₂ concentrations measured at Mauna Loa Observatory from 1958 to the present. The graph shows a steady increase in CO₂ levels from approximately 315 parts per million (ppm) in 1958 to over 420 ppm in recent years. The annual oscillations reflect seasonal variations in plant growth and decay, while the overall upward trend highlights the impact of human activities, particularly the burning of fossil fuels, on global atmospheric CO₂ levels. (ME)
Alarm grew as more information did. During the 1970s, scientists began developing early climate models to predict how the Earth would be affected by rising concentrations of greenhouse gases. The models tested different scenarios of emissions and suggested that continued fossil fuel use would likely lead to global temperature increases, altering rainfall patterns, and rising sea levels. While these early models were simple by today’s standards, they all suggested human-caused warming as a possibility. Scientists also began exploring how feedback processes, such as ice melting reducing Earth’s reflectivity, could reinforce these effects. (ME)
Despite these warnings, public awareness of climate change remained low, and political momentum stalled. The 1970s also saw the advent of climate skepticism, with some scientists and commentators suggesting observed warming was due to human actions or simply part of a natural fluctuation. There was also confusion over short-term cooling trends in the mid-20th century, later accounted for by aerosol pollution temporarily blocking sunlight. These points of argument inserted uncertainty into public discourse, even as scientific consensus began to coalesce around the role of greenhouse gases. (ME)
By the late 1980s, the evidence was difficult to deny. In 1988, NASA scientist James Hansen testified before the U.S. Congress recognizing that the Earth was warming and that human emissions were likely to blame. That same year, the United Nations and the World Meteorological Organization formed the Intergovernmental Panel on Climate Change (IPCC) to assess the science and inform global policymakers. The formation of the IPCC marked a shift from scientific inquiry to public awareness and international collaboration. (ME)
By 1989, the scientific understanding of climate change had evolved from broad observations of heat trapping into a sophisticated, data-driven picture of how humans were altering Earth’s climate system. The evidence was emerging from multiple fields of science, physics, chemistry, meteorology, and geology, and all pointing to the same conclusion: greenhouse gases trap heat, and the burning of fossil fuels was causing those gases to rise faster than at any point in recorded history. (ME)
The science of climate developed the possibility of international action. In the concluding section, we examine how growing awareness gave rise to the initial environmental movements, international agreements, and policy attempts to manage climate change, right as the modern age of climate policy was about to begin. (ME)
Global Awareness and Political Beginnings
By the close of the 20th century, scientific information on climate change had reached a tipping point. as had public interest. What once was the realm of laboratory study and scientific articles was now the subject of political debate, environmental activism, and international negotiation. This transformation did not happen overnight; it was the result of decades of consciousness-raising, public education, and environmental crises that pushed climate and ecological issues onto the global stage. By the time the world entered 1989, the ground had been prepared for a global response to human-caused climate change. (ME)
One of the earliest seeds of environmental awareness came in 1962 with the publication of Rachel Carson’s Silent Spring. The book exposed the dangers of widespread pesticide use and launched national discussion of human impacts on the natural world. While Silent Spring addressed primarily pollution and ecosystem degradation, it helped accelerate a general environmental movement that soon included air quality, conservation, and eventually the climate itself (US EPA, 2019). (ME)
Momentum continued to build in the 1960s and 70s. The first Earth Day, April 22, 1970, in the United States saw millions of people take to the streets to demand environmental protection. It was one of the biggest public demonstrations in U.S. history and led to a wave of environmental legislation. That same year, the U.S. government created the Environmental Protection Agency (EPA) to oversee pollution and enact environmental laws, a sign that environmental health had become a national priority (History.com Editors, 2017). (ME)
The growing environmental movement did not take long to reach the global stage. In 1972, the United Nations Conference on the Human Environment was held in Stockholm, the first global conference dedicated solely to environmental issues. Delegates from over 100 countries attended, recognizing that pollution, resource depletion, and environmental degradation were problems that knew no borders and required global solutions. Climate change was not yet the main issue, but the Stockholm conference laid the groundwork for international cooperation on environmental issues (United Nations, n.d.). (ME)
As science on climate change developed, international organizations began to respond more overtly. The First World Climate Conference was held in Geneva in 1979. Sponsored by the World Meteorological Organization (WMO), the conference brought together scientists and policymakers to discuss the impacts of climate variability and the need for long-term climate monitoring. It was the first time climate was discussed as a matter of international concern in a diplomatic setting (History of IMO and WMO, 2023). (ME)
During the 1980s, evidence of human impact on the atmosphere became undeniable — particularly with the ozone layer depletion. In 1985, governments signed the Vienna Convention for the Protection of the Ozone Layer, an international agreement to research and monitor the depleting ozone shield. Just two years later, this effort led to the Montreal Protocol, the historic agreement in which nations agreed to phase out ozone-depleting chemicals like chlorofluorocarbons (CFCs). While the Montreal Protocol did not address carbon emissions or climate change specifically, it showed that the international community could come together to combat a shared environmental threat and succeed. The treaty remains one of the finest instances of global environmental collaboration. (ME)
As concern mounted and scientific evidence became increasingly hard to ignore, the next landmark came in 1988: the establishment of the Intergovernmental Panel on Climate Change (IPCC). The United Nations and WMO founded the IPCC to gather and assess scientific research on climate change, its impacts, and potential policy responses. The IPCC’s task was not to conduct new science but to provide authoritative syntheses of existing knowledge to the governments of the world. Its creation reflected a growing international consensus that climate change was not only real, but also required concerted, science-based response (Le Treut & Somerville, 2007). (ME)
By the late 1980s, the world was no longer in the dark about climate change. Scientists had confirmed that human activities, especially the combustion of fossil fuels and the destruction of forests, were increasing greenhouse gases. Activists and educators had warned the public about environmental threats. Governments have begun experimenting with new laws and agreements to protect the atmosphere. And the global community had established the IPCC as a hub of climate knowledge. (ME)
The year 1989 was a turning point. Big climate action was still in its infancy, but the stage had been set for it. The world entered the 1990s with the definite understanding that climate change was real, largely human-caused, and increasingly urgent by the day. The challenge ahead would be turning knowledge into action, a process that would unfold over the decades to come. (ME)
Word count without personal reflection: 4173
Word count with personal reflection: 4599