In this blog post, we’ll examine the process by which scientific theories are formed and verified through the lens of climate change skepticism and the debate surrounding the “hockey stick” graph.
A glance at various media outlets—such as newspapers, television, and the internet—shows that climate change, epitomized by global warming, has become deeply embedded in our daily lives. Some of you may recall advertisements featuring polar bears precariously perched on melting glaciers. Such advertisements imply that if the Earth’s average temperature continues to rise at the current rate, humanity—symbolized by the polar bear—and various other forms of life could face serious danger. In addition, we frequently encounter public service announcements highlighting the severity of climate change by showing melting glaciers or various natural disasters occurring around the world.
However, from the perspective of a scientist studying climate change, viewing these ads may raise a few questions. This is because many ads present two points as self-evident facts without much scientific explanation: first, that the Earth is warming due to carbon dioxide emissions from humans, and second, that climate change is causing catastrophic damage to the environment. So, does everyone actually agree with these claims?
Global warming, as the term suggests, refers to the phenomenon of the Earth’s average temperature rising, and it is the most representative manifestation of recent climate change. Furthermore, it is understood as a concept that encompasses not only a simple rise in temperature but also various phenomena that threaten the survival of not only humanity but also diverse forms of life—such as melting glaciers, rising sea levels, extreme weather events, and changes in the habitats of living organisms.
A glacier is ice formed on land through the repeated accumulation and compression of snow over a long period. An ice sheet refers to a massive continental glacier covering a vast area. An ice shelf is a thick layer of ice that flows from a glacier or ice sheet toward the coast and floats on the ocean. An iceberg is a piece of ice that has broken off from a glacier or ice shelf and floats in the ocean, while pack ice refers to a large accumulation of such ice over a wide area. Sea ice is ice formed by the freezing of seawater. Therefore, the melting of icebergs or sea ice alone does not cause sea levels to rise.
Because the Earth’s climate system is extremely complex, it is difficult to pinpoint a single cause of climate change. However, based on a synthesis of research findings to date, the causes can be broadly categorized into natural and anthropogenic factors.
A prime example of a natural factor is the Sun. Due to the Earth’s orbital and rotational movements, its distance from and position relative to the Sun are not constant, and these variations have a significant impact on the climate. Furthermore, because the Earth’s tilted axis of rotation prevents solar energy from being distributed evenly across the globe, the atmosphere and oceans continuously circulate to redistribute heat; these circulations also have a major impact on the climate. In addition, volcanic ash and fine particles emitted by volcanic activity partially block solar radiation in the atmosphere, which can temporarily lower global temperatures.
On the other hand, anthropogenic factors include greenhouse gas emissions, aerosol production, deforestation, and land development. According to the body of research accumulated to date, recent global warming cannot be explained by natural factors alone, and the influence of anthropogenic factors is considered to be very significant. In particular, the scientific community widely agrees that the intensification of the greenhouse effect—driven by the rapid increase in greenhouse gas emissions since the Industrial Revolution—is the most significant cause of recent climate change.
Looking at public awareness campaigns by the government and corporations, as well as public perception, it appears that the view that human activities are causing global warming is relatively widely accepted in South Korea. However, not everyone around the world shares this view. For example, a look at the results of the “Climate Change in the American Mind” survey—conducted jointly by Yale University’s Climate Change Communication Project and George Mason University—reveals that perceptions of climate change are not uniform.
This survey is still conducted regularly, and while the results vary somewhat depending on the survey period, recent findings indicate that a majority of Americans agree that global warming is occurring and that human activity plays a significant role in causing it. However, perceptions of climate change and views on policy still differ depending on political leanings and social background.
In fact, the theory of global warming has evolved over a long period through various debates and counterarguments, and some disagreements still exist today. In particular, since climate change is an issue that significantly impacts not only science but also politics, the economy, and society as a whole, a wide range of stakeholders are participating in the discussion, and their perspectives on the matter differ. While early opposition often denied global warming itself, such outright denials have significantly diminished as observational data and research findings have widely confirmed that the Earth’s average temperature is rising. Today, the core of the debate centers not on whether climate change is actually occurring, but on whether recent warming is primarily caused by human activity or whether natural climate variability has played a greater role. Some argue that the current rise in temperatures is part of natural climate variability and that the human influence has been exaggerated. This viewpoint is generally referred to as “climate change skepticism,” and individuals or organizations that espouse these views are called “climate skeptics.”
One of the most prominent points of contention between proponents of climate change and climate skeptics is the “hockey stick graph.” This graph was created by American climatologist Michael Mann, who reconstructed temperature changes in the Northern Hemisphere over the past approximately 1,000 years using various climate proxies, such as tree rings and ice cores. It was named the “hockey stick graph” because its shape—remaining relatively stable for a long period before rising sharply after the Industrial Revolution—resembles a hockey stick. After being first published in a 1998 paper, the graph was included in the IPCC’s Third Assessment Report in 2001, becoming one of the most iconic pieces of evidence symbolizing global warming.
One of the primary methods for estimating past temperatures involves analyzing oxygen isotopes contained in ice cores—cylindrical samples extracted from ice sheets. Oxygen has isotopes with mass numbers of 16, 17, and 18, and in nature, oxygen with a mass number of 16 is the most abundant. Water also exhibits slightly different properties depending on the mass of the oxygen it contains; generally, lighter water evaporates more easily. As temperatures rise, evaporation increases, causing the ratio of heavier isotopes in the atmosphere to change. By utilizing this characteristic, past temperatures can be estimated by analyzing the isotope ratios within ice cores; today, researchers use not only oxygen isotopes but also various other climate proxies to reconstruct past climates.
Michael Mann, widely known for the “hockey stick” graph, also became the target of significant criticism surrounding this research. In 2003, Canadian mathematician Stephen McIntyre and economist Ross McKitrick published a reanalysis, arguing that there were problems with the statistical methods used in Mann’s study. Since then, some climate skeptics have continuously raised concerns about the research methods and data processing, and this controversy has attracted significant attention not only within the scientific community but also in politics and the media.
As the controversy grew, the “hockey stick” graph became the subject of a review by the U.S. National Research Council (NRC). In its 2006 report, the NRC assessed that the initial study contained some statistical limitations and uncertainties, noting that temperature estimates prior to 1600 were subject to relatively greater uncertainty. However, it concluded that even taking these limitations into account, the overall finding of a rapid rise in temperature over the past few centuries was generally consistent with the evidence available at the time. Since then, various research teams have presented similar results using different data and analytical methods, and the recent trend of rapid warming has been repeatedly confirmed by multiple independent studies.
As such, climate change research has evolved through numerous debates and verification processes. Although criticisms regarding errors, biases, or conflicts of interest in some studies were raised during this process, these findings have been continuously validated through new data and analytical methods. Currently, major global scientific societies and international scientific organizations, including the IPCC, have reached a broad consensus that the evidence supporting recent global warming and the influence of human activities is very strong.
All scientific theories developed by humans can be revised or supplemented when new evidence is discovered; they are not accepted as absolute truths. Just as the geocentric model was replaced by the heliocentric model in the past, science advances through constant verification and debate. However, this process is not a weakness of science but rather its most important characteristic. Reaching reliable conclusions through thorough verification and discussion from diverse perspectives is the essence of science, and climate change is a subject that must also be understood through this process. Therefore, correctly understanding the nature of scientific theories and maintaining a critical mindset based on diverse research findings and evidence are essential attitudes for navigating modern society.
