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All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

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Climate Hustle

Climate Scientists Talk Climate Change

Climate Scientists Talk Climate Change gives a voice to climate scientists who explain in a few words what their field of research tells us about climate change.

NOTE: this page is under construction. Click here for more info or to submit a quote .

Water Resources

One of the consequences of society's failure to act to reduce greenhouse gas emissions is that we are now faced with unavoidable and increasingly severe climate change. The best that we can now hope for is to work to avoid those climate impacts that will be socially, environmentally, and politically unmanageable while also figuring out how to manage those climate impacts we can no longer avoid.

The hydrologic cycle lies at the heart of the climate cycle, and as we change the climate we will be faced with increasingly complex and disruptive consequences for our water resources and the systems we've built to manage them.

Peter Gleick

President, Pacific Institute. Member, US National Academy of Sciences

Surface and Atmospheric Climate Change

The essential findings of mainstream climate change science are firm. The world is warming. There are many kinds of evidence: air temperatures, ocean temperatures, melting ice, rising sea levels, and much more. Human activities are the main cause. The warming is not natural. It is not due to the sun, for example. We know this because we can measure the effect of man-made carbon dioxide and it is much stronger than that of changes in the sun, which we also measure.

The greenhouse effect is well understood. It is as real as gravity. The foundations of the science are more than 150 years old. Carbon dioxide in the atmosphere traps heat. We know carbon dioxide is increasing because we measure it. We know the increase is due to human activities like burning fossil fuels because we can analyze the chemical evidence for that.

Richard Somerville

Distinguished Professor Emeritus & Research Professor at Scripps Institution of Oceanography, University of California

Greenhouse warming is physics. You can see the changes over time from the satellite observations that show how the greenhouse gases are blocking more of it. If you were to say there’s no greenhouse warming from CO2, that it doesn’t matter, you would be violating physics, you would be violating the facts that the satellites see. If CO2 did not warm, Earth would be largely or completely frozen — a snowball. You would also be unable to explain the history of the Earth’s climate.

Richard Alley

Evan Pugh Professor, Department of Geosciences, and Earth and Environmental Systems Institute, Pennsylvania State University

It all fits together. It's this coherence of data, and even if any one of these data set is wrong, it really would not affect your confidence because we have so much other data which suggests it's warming and because of this the IPCC calls this unequivocal, which means essentially beyond doubt. The key thing to look at is look for coherence, look for lots of evidence supporting a point and you will clearly see why scientists are convinced that the mainstream view of climate science is right.

Andrew Dessler

Professor, Department of Atmospheric Science, Texas A&M University

CO2 molecules emit thermal radiation (commonly known as heat). Adding energy to the surface by radiation tends to warm the surface. Doubling CO2 in Earth's atmosphere would add 4 watts to every square meter of the Earth's surface. This is equivalent to running a child's night light on every square meter permanently. If China and India achieve their goals of economic development using fossil fuels as the west has done (and who could blame them?), atmospheric CO2 will be close to 400% of preindustrial by the end of this century. Not double, but double double. So not one but TWO 4-watt nightlights on every square meter, permanently. CO2 removal depends on dissolving in the oceans. The physical mixing of the oceans takes about 1000 years, so it will take several millennia for the 2 4-watt bulbs to be turned off.

Scott Denning

Professor, Department of Atmospheric Science, Colorado State University

Climate has varied a lot in the past, due to natural factors. So how do we know that recent climate change is mostly due to increasing greenhouse gases in the atmosphere?

The climate responses to different factors, such as increases in solar radiation, major volcanic eruptions or increases in greenhouse gases, have different spatial patterns (fingerprints). For example, increases in solar radiation cause warming in the stratosphere and warming in the troposphere. Over the last 30 years, observations show cooling in the stratosphere and warming in the troposphere, the response expected from increases in greenhouse gases.

Other aspects of the observed pattern of warming, such as more warming in winter than in summer, are consistent with the response to increasing greenhouse gases but not consistent with the response to increasing solar radiation.

These and many other lines of evidence lead to the conclusion that most of the global-scale increase in temperatures over the last 50 years is due to the increase in greenhouse gases in the atmosphere.

David Karoly

Professor of Meteorology, University of Melbourne

Over the last century, we have observed large and coherent changes in many different aspects of Earth's climate. The oceans and land surface have warmed. The stratosphere has cooled, and the troposphere has warmed. Ocean heat content and atmospheric moisture have increased. Rainfall and surface pressure patterns have changed. Glaciers have retreated over most of the globe. Sea level has risen. The Greenland Ice Sheet is losing mass and contributing to sea level rise. Arctic sea-ice extent has decreased. Collectively, these changes are not consistent with natural causation alone. They /are/ consistent with our scientific understanding of how the climate system should be responding to anthropogenic forcing. The bottom-line is that the "fingerprint" of human effects on climate is not only visible through sophisticated statistical analyses - it is becoming increasingly apparent in our direct daily experience of the physical world.

Ben Santer

Research Scientist, Lawrence Livermore National Laboratory

Climate change poses extremely serious risks to society because physical systems, biological resources, and social institutions that humans depend on are highly adapted to existing climate conditions. Our greenhouse gas emissions disrupt those climate conditions. Basic principles show that we can reduce climate change risks, improve the economy, and expand personal freedom. Those who say otherwise spread fear with false facts and misunderstanding.

Paul Higgins

Senior Policy Fellow, American Meteorological Society Policy Program

Like all sciences, climate science is rife with mystery and unknown. Yet the warming of the globe in recent decades and the role of humans in modifying atmospheric composition are clear.

It is primarily the nuances of future climate (e.g. how much warming will occur? where will drought worsen and by how much?) that are uncertain and these questions propel current research efforts.

Successfully conveying to the public these knowns, uncertainties, and compelling outstanding issues exists as one of the great challenges of the 21st century and is a key role filled by Skeptical Science and others.

John Fasullo

Project Scientist, National Center for Atmospheric Research


The paleoclimate record shouts out to us that, far from being self-stabilizing, the Earth’s climate system is an ornery beast which overreacts even to small nudges.

Wally Broecker

Newberry Professor of Geology, Department of Earth and Environmental Sciences, Columbia University

Science is always evolving intellectually, processing, and incorporating the latest information, pushing out the frontier with the unknown. Scientists always want more data, more knowledge. However, even in the face of all the uncertainties and unknowns, and they are legion, everything I've learned about the dynamism of Earth's past climate places me, like most of my colleagues, strongly in the camp that says we need to take preventive action to keep the planet from warming further. I am extremely concerned that we've made such large changes in the composition of our atmosphere with so little understanding of the potential consequences.

Maureen Raymo

Research Professor, Dept. of Earth Sciences, Boston University


The scientific consensus is that we are pushing the world's oceans into conditions not seen for more than 40 million years. The accompanying changes in temperature and acidity are driving major impacts on biological systems from polar seas and the tropics. As a result, we may well lose ecosystems like the Great Barrier Reef within the next 30-50 years. Of equal importance is the rapid decline in gas exchange (providing oxygen and absorbing carbon dioxide) and primary productivity (which ultimately underpins food security) by the ocean. If these services continue to decline, much of life on Earth will be severely threatened. It is essential that we look at the evidence being provided by the world best scientists and act decisively to reduce these massive risks if they exist.

Ove Hoegh-Guldberg

Professor and Dir, Global Change Institute, University of Queensland

Nearly all of the debate - or at least what is depicted in the media as a debate - about global warming has focused on land surface temperatures. However, over 85 percent of the extra energy trapped by greenhouse gases has gone into the ocean. We all call this man-made catastrophe “global warming” or “climate change,” but “ocean warming” and “ocean change” are really more descriptive of what is happening. These changes go far beyond death, extinctions and habitat loss: fundamental processes are being altered, communities are being reorganized and ecological surprises are likely.

John Bruno

Associate Professor, The University of North Carolina at Chapel Hill

The impacts of human induced climate change have been rigorously detected in the physical, biological and chemical properties of our planet. One no longer needs advanced pattern detection methods to know the predictions from global climate models are upon us. They are obvious to even casual observers from the Arctic to the Equator and from the ocean depths to the Himalayas. The so called ‘tipping point’ was reached some time ago and it serves no purpose to continue that carnard. We know that even if we stopped greenhouse gas emissions today, the planet would continue to warm for decades and sea level rise for centuries. Our only option is to adapt to coming changes, changes that will tear the fabric of our society.

Tim Barnett

Marine Physicist Emertius, Scripps Institution of Oceanography, La Jolla, CA 92037

Natural Hazards and Policy

Our bond with the Earth? The Earth is at one and the same time a resource, a victim, and a threat. We can go only so far considering each of these dimensions in isolation! In our natural and social science, our policy analysis, and our practice, we must master this full relationship. At all times. Everywhere.

And in the business of life, our carbon footprint should be our least consequential footprint.

William Hooke

Senior Policy Fellow, American Meteorological Society


We are living in a world that is beginning to experience climatic conditions that are unfamiliar to modern societies and the world's ice cover is already responding dramatically to these changes. It is dangerous to ignore this or to deny that it is happening, especially since there are over 6.8 billion people on Earth competing for resources that make life possible, but that also are impacted by climate change.

Lonnie Thompson

Distinguished University Professor, School of Earth Sciences and Bryd Polar Research Center, Ohio State University

We are starting to see the consequences of climate change, particularly in the Arctic. Climate models for a long time have predicted that the Arctic will transition towards a seasonally ice free Arctic Ocean as atmospheric concentrations of greenhouse gases continue to increase. Today the Arctic sea ice is shrinking faster than any of our climate models have predicted and scientists now expect that the Arctic Ocean will be ice free during summers sometime between 2030 and 2100. This rapid pace of ice loss is already contributing to amplified warming in the region.

Julienne Stroeve

Research Scientist, National Snow and Ice Data Center, University of Colorado

I think that Nature's best thermometer, perhaps its most sensitive and unambiguous indicator of climate change, is ice. When ice gets sufficiently warm, it melts. And, in the context of the heated political environment that has fueled the climate change debate in recent years, ice is entirely neutral in its testimony. Ice asks no questions, presents no arguments, reads no newspapers, listens to no debates. It is not burdened by ideology, and carries no political baggage as it crosses the threshold from solid to liquid. It just melts.

Henry Pollack

Professor of Geophysics, Department of Geological Sciences, University of Michigan

Climate Models

You don't need a fancy "climate model" to tell you that greenhouse gas increases must warm the planet -- it was recognised by leading scientists as soon as they discovered these gases a century and a half ago. Everything that has happened since then has confirmed their predictions.

Steven Sherwood

Professor, Climate Change Research Centre, UNSW, Australia

Scientific evidence for the reality of human-caused climate change includes independently replicated data documenting the extent of warming; unprecedented melting of glaciers; rises in global sea levels; increasingly widespread continental drought; and models that predict all of these things but only when human impacts are included. Those same models project far more profound and potentially damaging impacts of climate change if we do not take action to stabilize greenhouse gas levels.

Michael Mann

Director of the Earth System Science Center, Pennsylvania State University

Climate scientists predicted global warming 35 years ago, before there was any sign of warming. Computer models of 20 years ago accurately predicted the rate of global warming. There is no reason to doubt the predictions for the future. The predictions have been correct because they are based on fundamental physics. This is not a hoax, this a profound demonstration of the scientific method. Society should be proud of climate science. Questioning the reality of climate change and the validity of climate science is not a challenge within scientific culture, but a demonstration of how our society can be manipulated through the modern media.

Kevin Judd

Professor, School of Mathematics and Statistics, The University of Western Australia


Direct impacts of climate change on the biosphere are now becoming evident. In dry forests, large wildfires are becoming more regular, and massive insect epidemics triggered by tree stress are becoming common. Declining snowpacks are causing smaller streams to dry up in late summer, killing trout populations. Hibernating animals such as bears are becoming confused over when to go in to and when to emerge from their wintering dens. The seasonal timing of bird and butterfly migration is being disrupted. Coral reefs in the oceans are dying. How much more ecosystem degradation will occur before humanity wakes up?

Steven Running

Director, Numerical Terradynamic Simulation Group, Dept. of Ecosystem Sciences, University of Montana

More than half of all wild species studied have responded to recent climate change. Species restricted to cold climate habitats (polar bears in the Artic, Emperor penguins in Antarctica and pikas on mountain tops) and with narrow temperature tolerances (tropical corals) have been most harmed by global warming, forced to shrink where they live as suitable climate space disappears. Species are not evolving fast enough to prevent extinctions in our lifetime. Conservation in a time of such major, rapid climate change will require a fundamental rethinking of what it means to preserve "biodiversity."

Camille Parmesan

Professor Integrative Biology, University of Texas at Austin


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