People often use the term "climate deniers" to describe individuals or groups who reject some aspect of the scientific consensus on climate change. Their arguments vary considerably; some reject that warming is occurring, while others accept warming but dispute its causes, severity, or policy implications.
Here are the main scientific arguments commonly put forward, along with how mainstream climate science evaluates them:
Argument: Earth's climate has undergone natural warming and cooling cycles long before humans existed, so current warming could be natural.
Mainstream scientific response: Climate scientists agree that climate changes naturally. The key question is what is causing the current warming. Multiple lines of evidence indicate that the rapid warming since the late 19th century is primarily due to human emissions of greenhouse gases, especially carbon dioxide. Natural factors such as solar activity and volcanic activity do not explain the observed warming pattern. Intergovernmental Panel on Climate Change
Argument: CO₂ is only a trace gas in the atmosphere, so it cannot have a large effect on climate.
Mainstream scientific response: Although CO₂ constitutes a small fraction of the atmosphere, its infrared-absorbing properties have been understood since the 19th century. The greenhouse effect is a well-established physical phenomenon. Climate scientists argue that even relatively small changes in greenhouse gas concentrations can significantly affect Earth's energy balance.
Argument: Changes in solar output explain recent temperature increases.
Mainstream scientific response: Solar variations do influence climate, but satellite measurements since the late 20th century show no long-term increase in solar energy sufficient to explain the observed warming. Temperatures have continued to rise even while solar activity has remained relatively stable.
Argument: Climate models contain uncertainties and have sometimes made inaccurate predictions.
Mainstream scientific response: Scientists acknowledge uncertainties in models. However, climate models are based on established physical laws and have successfully reproduced many large-scale climate trends. The existence of uncertainty does not imply that the models are useless; rather, it affects the precision of projections.
Argument: Weather stations are affected by urban development ("urban heat island" effects), and temperature records may therefore exaggerate warming.
Mainstream scientific response: Researchers account for urban heat island effects using various correction methods. Independent temperature records from satellites, ocean measurements, glaciers, and other indicators all show warming trends consistent with surface temperature records.
Argument: There is insufficient evidence that climate change is increasing hurricanes, floods, droughts, or other extreme events.
Mainstream scientific response: Attribution varies by event type. Scientists generally find stronger evidence for increases in heat waves, heavy precipitation events, and some drought conditions, while trends in other phenomena may be more complex and region-specific.
Argument: The climate system may be less sensitive to CO₂ than mainstream estimates suggest, leading to less future warming.
Mainstream scientific response: Climate sensitivity remains an active area of research. While estimates have been refined over time, most studies continue to find that substantial warming results from increased greenhouse gas concentrations.
Argument: There is more disagreement among scientists than is often portrayed.
Mainstream scientific response: Surveys and literature reviews generally find broad agreement among climate scientists that recent warming is occurring and that human activities are the dominant cause. Debate continues over details such as regional impacts, feedbacks, and policy responses, but not over the basic conclusion.
Argument: A warmer climate could increase agricultural productivity, reduce cold-weather deaths, and have net positive effects.
Scientists acknowledge that some regions may experience certain benefits. However, most assessments conclude that, beyond modest warming levels, the overall global impacts become increasingly negative, including risks to ecosystems, agriculture, water resources, and coastal areas.
Scientific skepticism — questioning evidence, models, assumptions, or uncertainties within the scientific process. Climate-change skepticism — disputing one or more aspects of the mainstream view. Climate-change denial — rejecting well-established evidence despite extensive supporting data.
Many people grouped together as "climate deniers" actually hold different positions, ranging from legitimate scientific critiques of specific studies to outright rejection of the evidence for human-caused warming.
Today, the mainstream scientific position, represented by organizations such as the Intergovernmental Panel on Climate Change, National Aeronautics and Space Administration, and the National Oceanic and Atmospheric Administration, is that the Earth is warming and that human emissions of greenhouse gases are the primary cause of the warming observed since the mid-20th century.
The mainstream IPCC position is that human greenhouse-gas emissions have unequivocally caused global warming.
Richard Lindzen (MIT emeritus professor of meteorology; dynamical meteorologist), William Happer (Princeton emeritus physics professor; PhD physics, Princeton), Patrick Michaels (PhD ecological climatology, University of Wisconsin) Roy Spencer (PhD meteorology, University of Wisconsin; former NASA climate scientist, UAH principal research scientist).
Christy (distinguished Professor of Atmospheric Science and Director, Earth System Science Center, University of Alabama in Huntsville; co-developed satellite temperature dataset) and Roy Spencer and (co-recipient with Christy of NASA medal for satellite temperature monitoring).
oceans, clouds, volcanoes, internal cycles and chaotic variability may explain more observed change than accepted.
Judith Curry, Richard Lindzen Curry: climatologist; former chair, School of Earth and Atmospheric Sciences, Georgia Tech; PhD atmospheric science, University of Chicago. Lindzen: MIT meteorology professor with work on atmospheric dynamics and climate sensitivity.
Willie Soon, formerly S. Fred Singer Soon: astrophysicist/aerospace engineer; PhD from University of Southern California; formerly Harvard–Smithsonian Center for Astrophysics. Singer: atmospheric and space physicist; professor emeritus of environmental science, University of Virginia.
Medieval Warm Period, Little Ice Age and proxy uncertainties are used to argue modern warming is not exceptional.
Willie Soon, Sallie Baliunas, Fred Singer Soon’s 2003 proxy-temperature work was widely criticised for methods, including mixing moisture and temperature proxies and regional versus hemispheric evidence.
CO₂ fertilisation, fewer cold deaths, and adaptation are emphasised over climate damages.
William Happer, Patrick Michaels, John Christy Happer argues CO₂’s harms are overstated; Michaels argued warming would be limited and not catastrophic; Christy has argued fossil energy has major human-development benefits.
Many of these scientists do not deny that CO₂ is a greenhouse gas or that warming has occurred. Their dissent is usually about magnitude, attribution, model reliability, and risk severity. Their views remain minority positions against the IPCC assessment - the so-called 'sientific consensus'.