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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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John Garrett is a technical illustrator residing in Wildomar, California, USA. In my personal time, I volunteer for a variety of groups including Skeptical Science, the Santa Rosa Plateau Ecological Reserve, and the Temecula Valley Astronomers. As an astronomy enthusiast, I’ve published photos in Astronomy Magazine and am involved in establishing astronomy clubs in local middle schools. I’m also a member of the International Dark-sky Association.


Recent blog posts

SkS Analogy 21 - Snow on a Hot Tin Roof

Posted on 17 December 2019 by Evan

With many feet of snow on our shed roof and with another winter storm approaching, I knew I had to get some of the snow off the roof to prevent its collapse. So, I worked for a couple of days pulling off some of the snow. When I finished there was a thin layer of remaining snow over most of the roof, and the sheet metal at the edge of the roof was exposed, bare metal.

In the following days I noticed that the amount of bare metal kept getting bigger and bigger, moving up from the edge of the roof towards the peak of the roof. This did not happen with a nice, uniform layer of snow on the roof, all the way down to the edge. For months the snow had not retreated, but once I exposed the edge of the tin roof, the snow started retreating, exposing the tin roof as the snow line proceeded on its upward march towards the peak of the roof.

Of course, you know what was happening. White snow reflects most of the sunlight, keeping the snow cool. But when even a sliver of metal roof is cleared of snow, the sunlight hits it, warming it up, because the tin roof absorbs most of the sunlight. Now that the tin is warm, the snow next to the tin melts, causing more tin to be exposed, causing the larger amount of exposed tin to absorb more heat, etc. What started as only a sliver of metal exposed on the edges and a small amount of melting, soon turned into a rapidly increasing fraction of the roof being cleared of snow, accelerating the local warming and the melting of snow. Before long the snow on the shed roof had melted all the way to the peak of the roof and cleared itself off.

Snow on a hot tin roof


This phenomenon is called the ice-albedo feedback. “Albedo” is a fancy term that essentially means how white something is. Snow has a high albedo, and blacktop has an albedo near 0. Surfaces with high albedo reflect most of the sunlight, whereas surfaces with low albedo absorb most of the sunlight. The idea of the ice-albedo feedback is that when snow is sitting on top of something that has a low albedo, like the snow on our tin roof or like the ice on top of the Arctic ocean, the dark surface near the ice melts more ice or snow, which exposes more dark surface underneath, which causes more warming, which melts more ice or snow, and so on and so forth until soon a large area of snow or ice is melted. One of the only things that interrupts this process is that at some point the sun sets, allowing the environment to cool. This interrupts the ice-albedo feedback because the sunlight that drives the warming is not available during polar night. In Minnesota the sun rises and sets once a day, but in the Arctic there is a period when the sun sets and does not rise again for many months, just as there is also a period when the sun never sets, allowing the ice-albedo feedback to proceed unchecked for months at a time.



SkS Analogy 20 - The Tides of Earth

Posted on 5 September 2019 by Evan

Tag Line

Heavenly bodies regularly cause sea level to change by 0.5 to 120 m (2 to 400 ft).
Human bodies can cause sea level to change by 60 m (200 ft).

Elevator Statement

You’ve heard it said, “The climate is always changing.” What does that mean?

If someone said, “Mr. Smith is always falling down”, you would assume that Mr. Smith is unstable.

When you hear the phrase “The climate is always changing,” you might think, “I wonder why the climate is so unstable and always changing?” On 100,000-year cycles the global average temperature varies by 5°C, which causes variation in sea level of 120 m (400 ft). That is a lot!

These massive, 120-m glacial tides are caused by heavenly bodies that are hundreds of millions of miles away, tugging on what appears to be a very sensitive environmental system, causing regular, massive changes.

Is it possible that 8,000,000,000 human bodies pushing hard on this same, sensitive environmental system could cause a similar effect?

Jupiter and Saturn cause 100,000-year glacial tides



SkS Analogy 19 - A table full of crystal and ideal temperature

Posted on 7 March 2019 by Evan

Tag Line

A table stacked high with delicate crystal is beautiful to look at, but impossible to move without significant breakage.

Elevator Statement

Stack crystal plates, bowls, glasses, and figurines on top of each other on a table. Done by a skilled artist it is a pleasure to look at. But try to move this delicate work of art from one place to another. The faster you move it the more damage there will be. The more crystal that is placed on the table and the higher it is stacked, the more precarious it is to keep balanced, and the more breakage occurs if the table is moved.

If the table had been placed at a different location before stacking the crystal, it could have been filled with the same crystal and created a similar, beautiful masterpiece at a different location. But stacking the table full of crystal and then moving it to a new place causes significant breakage.

Table full of crystal
So it is when we populate Earth with 8 billion beautiful people, inhabiting all of the available habitable zones, and then alter the location of the habitable zones through rapid changes in temperature, precipitation, and storms. Increasing the average temperature of the earth is not so much the problem as is the rate at which we are changing the temperature. The faster we raise the temperature, the faster climate changes, the quicker that habitable zones move, and the less time there is to adapt (i.e., move from one habitable zone to another).

Some ask rhetorically what Earth’s ideal temperature is. This is like asking what a table’s ideal location is. Damage occurs to the crystal on a table not because it is or is not in the ideal location, but because the table is moved after it is fully loaded with delicate crystal.

To minimize breakage, a table stacked high with crystal must either be moved extremely slowly, or left in its current location.



SkS Analogy 18 - Cliff jumping and temperature changes

Posted on 30 January 2019 by Evan

Tag Line

Regardless the height of the cliff, jumping from cliffs is deadly.

Elevator Statement

Regardless of the height of a cliff, jumping from cliffs is deadly. Hang-gliding from cliffs thrills. Jumping from cliffs kills. Jumping 10 m from a cliff that is 1000 m above sea level hurts just as much as jumping 10 m from a cliff that is 900 m above sea level.

Increasing or decreasing the global average temperature causes sea level to rise or fall. Rapidly increasing or decreasing the global average temperature will likely cause sea level to rapidly rise or fall. It does not matter what the current global average temperature is. Causing the global average temperature to jump, as we are, causes sea level to jump. A snail can outrun sea level change, but houses, sky scrapers, buildings, subways, and roads move slower than snails. They sit where they are and drown. Are your children and grand children prepared for this coming future? Is there anything we can do to slow down the ongoing global temperature jump?

Cliff Jumping



SkS Analogy 17 - Lotteries, evaporation, and superstorms

Posted on 24 January 2019 by Evan

Tag Line

Evaporation is like a lottery. Lottery winners finance our storms.

Elevator Statement

Each day 10,000 people each put $100 into a million-dollar lottery where winner takes all. Because lottery winnings are taxed, the winner receives $600,000 and the government receives $400,000. This leaves the people who bought the lottery tickets poorer, one person richer, and the government more powerful.

A puddle of water loses water due to evaporation. Evaporation occurs when many neighboring molecules share a little of their energy with a single molecule that gains enough energy to leave the puddle and fly away into the atmosphere. This molecule wins the lottery. The high energy required to send a single water molecule into the atmosphere causes the energy of the other molecules in the puddle to decrease (i.e., the temperature of the puddle decreases), while the amount of water vapor in the atmosphere increases. A fraction of the water vapor in the atmosphere is available to storms, so that as the total amount of water vapor in the atmosphere increases, the amount available to storms also increases (i.e., the fraction of a larger number means more is available).  Because storms get their power from condensing water vapor, as more water vapor is added to the atmosphere more water vapor is available to storms, which increases their power. Therefore, evaporation leaves the puddle with a less energy, the atmosphere with more water vapor, and storms with more power. This is how evaporation keeps Earth cool and supercharges storms.

Evaporation adds power to the atmosphere



Climate Carbon Bookkeeping

Posted on 20 December 2018 by Evan

The question often arises as to how we know that the current year-to-year buildup of CO2 is due to human activities. One way is to do simple bookkeeping of how much of each of the major types of fossil fuels we burn each year, and the predicted CO2 buildup implied by the known yearly combustion rate. Burning fossil fuels produce two major products: CO2 and H2O. As long as we know the carbon and hydrogen content of each of the major types of fossil fuels, it is relatively straightforward to calculate the amount of CO2 released each year. The point of this article is to demonstrate how we do such a calculation, and to demonstrate that such a calculation clearly shows that the measured annual rise of CO2 is due to human activities.

Climate Carbon Bookkeeping

CO2 emissions occur primarily due to burning coal, oil, natural gas, and through deforestation. Because the consumption rates of coal, oil, and natural gas are known, and because other groups monitor the state of forests, it is easy to estimate the CO2 emissions from these sources. Part of the CO2 emitted accumulates in the atmosphere and remains there for centuries to millennia, but part of the CO2 emitted is quickly reabsorbed back into the biosphere (water, soil, and rocks). By using a rough estimate that about 50% of emissions are reabsorbed into the biosphere,  it is possible to estimate the atmospheric CO2 accumulation due to human emissions.

Before the Industrial Revolution (which started about 1800 AD) CO2 natural emissions were roughly in balance with CO2 natural sinks, for no net accumulation. This is demonstrated by CO2 estimated from ice-core samples for the period 1000 AD to present, shown in Figure 1. From the dawn of the Industrial Revolution until now atmospheric CO2 concentrations have been steadily increasing. It is easy to show that the atmospheric accumulation of CO2 since the dawn of the Industrial Revolution is due mostly to the burning of fossil fuels, because we know from year to year how much oil, natural gas, coal, and forest trees we are burning, and we know how many molecules are in the atmosphere. Given this data, we can calculate the expected annual increase in CO2 and compare it to the measured annual increase.

CO2 concentrations in Earth’s atmosphere are tracked as the number of CO2 molecules per million molecules [parts per million: ppm]. Figure 1 indicates that 200 years ago this value was about 280 ppm, whereas today it is close to 410 ppm, and from 2005 - 2014 it  increased an average of about 2.1 ppm/year. To see that this increase is due primarily to burning fossil fuels and deforestation, we simply divide the number of carbon atoms emitted from Anthropogenic sources by the number of molecules in the atmosphere. It requires a little math, but no computer models.

Figure 1. Atmospheric CO2 estimated from ice-core samples, combined with measurements that started in 1958 (represented by the dark blue line). This graph is available at



SkS Analogy 16 - Arctic ice, sailboat keels, and wild weather

Posted on 3 December 2018 by Evan

Tag Line

Slowly pull up the keel of a sailboat as it’s racing straight across a large lake, and soon it will begin to wallow around at the mercy of the wind.

Elevator Statement

In the physical world large differences cause the motion of things:

  • Heat flows from hot to cold (like from inside your warm house to the cold outside)
  • Water flows from high to low places (think waterfall)
  • Air flows from high to low pressure (like from inside an air compressor through the nozzle and out)

The temperature difference between the warm Equator and the cold Arctic causes large-scale air motion to the Arctic. Like a river raging straight down a steep mountain, a large temperature difference causes air to move northward from the Equator fast and straight, bending with the rotation of the Earth to create a well-behaved jet stream that moves from West to East.  The motion is reminiscent of a well-trimmed sailboat challenging the wind as it races straight and true across a large body of water.

It is well documented that the Arctic is warming at 2 to 4 times the global average rate (read here and here). This decreases the temperature difference between the Equator and the Arctic, which decreases the driving force for the Jet Stream winds. The weakened driving force allows the jet stream to wallow around, just like a river that slowly meanders back and forth when it hits an area with only a slight elevation change (think flat). The image is similar to how a sailboat flounders about when the keel is pulled up: moving at the mercy of the wind instead of challenging it. In the same way that healthy arctic ice is linked with a strong, healthy jet stream that tracks relatively straight and true around the earth, so too a strong, deep keel is linked to a sailboat that tracks straight and true.



SkS Analogy 15 - Ice Tea and Temperature Rise

Posted on 16 October 2018 by Evan

Tag Line

Even on a hot day, as long as your glass of tea has ice it is a nice, cool drink. Only when the ice disappears does your drink start to warm up.

Elevator Statement

The height of a balloon above the ground is not proportional to the amount of hot air you put into the envelope.1 In fact, when you first start filling a balloon all that happens is that the hot air causes the envelope to lift off of the ground, applying tension to the basket and its occupants, but there is no upward motion of the balloon at that point. You pump in more and more hot air, and if select US Senators were standing by they would likely proclaim that there is absolutely no effect of hot air on the balloon.

The problem, of course, is that a huge amount of hot air must be injected into the balloon just to overcome the weight of the envelope, the basket, and its occupants. As long as the upward force is less than the downward, restraining force, nothing happens. But once the upward force overcomes the downward force, up you go, and any small addition of hot air2 at this point causes you to accelerate faster and faster skyward.

Ever wonder why you put ice cubes into your water and not cold rocks? The difference between ice and rocks is that the temperature of a cold rock will slowly increase along with the liquid it is trying to keep cold, and will do no better keeping the liquid cool than the cool liquid itself. Cold rocks do nothing to keep your drink cool.

However, ice is effective because as long as there is ice in your glass, the combination of ice and tea will stay near 0°C. As soon as the ice melts and is completely gone the temperature of your tea starts to rise, and soon your drink becomes warm and tasteless. We have all used ice in our drinks, but likely without ever realizing that the reason for using ice is that by definition, the temperature of ice cannot rise above 0°C, whereas a cold rock will easily warm up past 0°C. So if there is ice in your glass, it stabilizes the temperature to near 0°C. Read on in the next section to learn about the property of ice that keeps your ice tea near 0°C.

In the last 40 years we’ve lost about 50% of the Arctic ice area and about 70% of the volume.3 Time to ask Earth’s bartender for more ice for our drink, lest the temperature of the Arctic becomes too warm.

Ice balloons temperature rise



SkS Analogy 14 - Inertia and Inevitability

Posted on 10 October 2018 by Evan

Tag Line

Inertia is your friend … until it isn’t.

Elevator Statement

Inertia delays the response …
  But for each CO2 level there is a guaranteed response …
        Be patient, the response is coming …
                     And when it finally comes there’s no going back.

Tie a rubber band to a weight. Move your hand rapidly1 away from the weight,2 stop your hand,3 wait, and the slowly accelerating weight will eventually slam into your hand.4

Think of your hand as CO2 concentration and the weight as atmospheric temperature. Moving your hand quickly is like rapidly increasing CO2 concentration.5 The motion of the weight is like rising atmospheric temperature, where the position of the weight is an indication of atmospheric temperature. A heavy weight causes a large time delay between the motion of your hand and the motion of the weight, similar to the delay between GreenHouse-Gas (GHG) emissions and warming caused by the thermal inertia of the oceans.

So just like connecting your hand to a weight with a rubber band, moving your hand quickly does not guarantee that the weight will initially move quickly. But if you are patient, and if you experiment by moving your hand at different rates, you will find that the quicker and further you move your hand the faster and harder the weight will eventually slam into your hand. You just have to be patient to let the weight catch up.

For another example of the effect of inertia in a system with a small force moving a large weight we turn to NASA. NASA uses solar-powered ion thrusters to power its current generation of deep-space voyagers. Ion thrusters use electrical energy provided by solar panels to accelerate individual xenon atoms, ejecting them at high velocity out the back of the rocket engine. The beauty of ion thrusters is that they combine an essentially infinite energy source (i.e., the sun), together with on-board fuel (xenon) to provide high-efficiency propulsion. The down side is that the thrust/weight ratio is so low that it may take months to years for the probe to reach maximum velocity.

Noting that the heating effect of GHGs in Earth’s atmosphere is relatively low, and that the mass of the oceans is massive, just as ion-thrust engines require months to years to accelerate their payload up to maximum speed, GHGs in Earth’s atmosphere require years to decades to accelerate their “payload” up to maximum temperature, with a typical cause-and-effect time constant of about 30 years: the length of a typical house mortgage.



SkS Analogy 13 - Water glasses and Greenhouse gases

Posted on 17 July 2018 by Evan

Tag Line

How do you add water to a full glass?

Elevator Statement

Adding water to a full glass causes the water to rain over the sides.
    Adding water vapor to saturated air causes mist, clouds, or rain to form.

To add water to a full glass, first increase the height of the glass.
    Adding greenhouse gases to the atmosphere causes warming, raising the dew point.

Then add more water to the larger glass.
    The higher dew point allows more water vapor to be added to the air.

Water glasses and greenhouse gases



SkS Analogy 12 - A Sinking ship reaches new heights

Posted on 15 May 2018 by Evan

Tag Line

A sinking ship reaches new heights.

Elevator Statement

For a sinking ship the stern may be unusually low, the bow unusually high, and on average, the whole thing is going down. We cannot infer what is happening to the ship just by what is happening to one part. We must look at the entire ship.

It seems that at least one US Senator did not understand this relationship between the environment’s local extremes and global means when he found snow in front of the US capital, in February, and thought it meant that Global Warming had stopped.1  If he had watched the news that night, he might have realized that just a few hundred miles to the south it was unusually hot in Florida.

If we wait to take action on Climate Change until it is obvious to everyone that the ship is sinking, we may all be swimming.


Climate Science

As the Earth warms, some parts will still be cold. Let’s face it, the North and South Poles are just cold places. Some parts may experience colder temperatures for a while in response to a modified jet stream that draws cold, Arctic air further south than in the past. Cold days still happen, just less frequently.



SkS Analogy 11 - Cabinets, airplanes, and frame of reference

Posted on 2 May 2018 by Evan

Tag Line

The elevation of an airplane landing on a runway is only useful if measured relative to the ground (i.e., height), and not to sea level (i.e., altitude).

Elevator Statement

While determining the optimum height for kitchen cabinets, an industrious husband in Minnesota asks his wife

“Should we move the kitchen cabinets up by 0.1% from the position we originally discussed?”

“Why on earth are you bothering me about such a trivial amount?” came the reply. “Now if you were considering something ridiculous like raising them 1 ft. I would complain.”

In fact, the husband was considering raising the kitchen cabinets by 1 ft. His reference to 0.1% used the height above sea level of 1000 ft. as the reference point for making his measurements. A ridiculous analogy you say? Climate-change deniers and not-so-well-informed skeptics make similar errors, but they are not as obvious. Read on if you want to learn the error that a Nobel Laureate made by miscommunicating in a similar manner as this industrious husband.

Climate Science

Nobel Laureate Ivar Giaever stated the following in a talk he gave on climate science,1

“From ~1880 to 2013 temperature increased from ~288K to 288.8K (0.3%). If this is true, to me it means that the temperature has been amazingly stable.”

A 0.3% increase is kind of like the 0.1% the husband raised the kitchen cabinets. Dr. Giaever was using an absolute temperature scale for his comparison. Unlike the Celsius temperature scale where 0°C is the point where ice melts, 0K on the absolute temperature scale is the point where atoms “melt” and start moving. For comparison, on the temperature scale that Dr. Giaever was using, ice melts at a blisteringly hot 273K. If you live in a coastal city prone to flooding, do you care more about the temperature at which atoms “melt” and start moving (i.e., 0K), or do you care more about the temperature at which ice melts (i.e., 273K = 0°C) and continues moving ever closer to your home?




New resource: The Fact-Myth-Fallacy slide-deck

Posted on 9 April 2018 by BaerbelW

Many of you will already be familiar with the Fact-Myth-Fallacy structure of a successful debunking. For a refresher, John Cook's post about "Inoculation theory: Using misinformation to fight misinformation" is a good primer on the topic.


As examples for how to make use of this structure, we have short debunkings of many of the myths covered in our MOOC Denial101x readily available on an overview page, which also includes the relevant video lecture for each of them. The list is also available as a PDF-file:



SkS Analogy 10 - Bathtubs and Budgets

Posted on 12 October 2017 by Evan

Tag Line

Adding 101 gallons to a 100-gallon bathtub causes it to overflow, even if added slowly.

Elevator Statement

No matter how slowly a bathtub is filled, adding more than 100 gallons of water to a 100-gallon bathtub causes it to overflow. This principle is clear, obvious, and one we encounter every time we take a bath.

Similar to the finite volume of a bathtub, Earth’s atmosphere has a finite volume. Because Earth’s atmosphere has a fixed volume, human emissions of greenhouse gases (GHGs) are increasing the atmospheric concentration of CO2, because we keep adding GHGs into this closed system, similar to running water into a bathtub.1 The concentration of CO2 does not depend on how rapidly we add GHGs to the atmosphere, but only on the total amount added.2 Lowering emission rates is important for improving the air quality in a large city, but carbon emission rates are meaningless for determining the global warming we will eventually experience due to a revved-up greenhouse effect: only the total amount emitted matters.3

Climate Science

The atmosphere has a budget of carbon it can accept to keep overall warming below a certain level, and the bathtub in this analogy is intended to be a visual representation of such a budget. Although scientists do not know with certainty how much the climate will warm for a doubling of CO2 (the so-called climate sensitivity), a climate sensitivity of 3°C/doubling of CO2 (see Ocean Time Lag)4 is consistent with the warming observed since the 1970’s, and is mid-range in the IPCC estimates that range from a low of 1.5 to a high of 4.5°C. Using a climate sensitivity of 3°C/doubling of CO2, a rough guide of the carbon budget corresponding to a particular level of warming is as follows5



SkS Analogy 6 - Speakers, tuning forks, and global warming

Posted on 29 May 2017 by Evan

Tag Line

The physics of global warming by greenhouse gases is well understood and can be illustrated by items we use every day.

Elevator Statement

Simple, well-understood physics indicate the following:

  • Sound waves vibrate speakers (think microphone1) and vibrating speakers make sound waves
  • Sound waves vibrate tuning forks and vibrating tuning forks make sound waves (with a narrow range of frequencies)
  • Infrared waves vibrate CO2 molecules (increased vibration means more energy, which means warmer) and vibrating CO2 molecules make infrared waves (think CO2 lasers, which make waves with a narrow range of frequencies)

Almost everybody is familiar with microphones, speakers, and tuning forks. These are items you can see, touch, and feel, so they are familiar. Even though we cannot see greenhouse gases like CO2, they operate the same as speakers and tuning forks: they absorb and reemit waves, just on a very small scale. When they absorb waves they trap heat, warming the atmosphere.

Tuning fork and CO2 molecule

Excitation of tuning fork by sound and CO2 molecule by infrared radiation (graphics by jg).



SkS Analogy 3 - The Greenhouse Effect is Like a Cloudy Night

Posted on 9 May 2017 by Evan

Tag Line

The greenhouse effect is like a warm, cloudy night.

Elevator Statement

  • At night clouds trap infrared radiation emitted from the ground, similar to greenhouse gases, and re-emit some of the absorbed radiation back to the ground.
  • More nighttime cloud cover means more trapped heat, and warmer temperatures near the ground, just as more CO2 in the atmosphere means more trapped heat, and warmer temperatures.
  • Because clouds are big and thick, their radiation-trapping effect is felt immediately, within a single night.
  • Because CO2 is diffuse, its effect is felt slowly, over many decades.
  • Increasing the concentration of CO2 in the atmosphere is like increasing the cloud cover at night: both warm the Earth by trapping infrared radiation.

Climate Science

The greenhouse effect describes the trapping of energy by Earth’s atmosphere: infrared radiation from the ground is absorbed by gases in the atmosphere such as CO2, H2O, CH4, and others. Although the greenhouse effect is active 24/7, it is most apparent at night. This is because with no background solar radiation, nighttime warmth occurs mostly by greenhouse gases and clouds grabbing and storing some of the infrared radiation emitted from the ground that is trying to make it to outer space. This is partly why nighttime temperatures have been steadily increasing as greenhouse gases increase: more greenhouse gases implies more heating.



SkS Analogy 2 - Ferrari Without Gas

Posted on 24 April 2017 by Evan

Tag Line

A Ferrari without gasoline goes nowhere.
Greenhouse gases without infrared radiation cause no warming.

Elevator Statement

  • The concentration of greenhouse gases is like the size of a car engine: higher greenhouse gas concentration is like a bigger engine.
  • Infrared radiation is like the gasoline in the tank of a car.
  • Just as gasoline is the fuel that drives an engine, infrared radiation is the fuel that drives the greenhouse effect.

Climate Science

Global warming occurs because infrared radiation emitted from the surface of the Earth is captured by greenhouse gases in the atmosphere, increasing the temperature of the atmosphere. Increased greenhouse-gas concentrations in an atmosphere with constant background infrared radiation will absorb an increasing fraction of the emitted infrared radiation, causing warming. Increased greenhouse-gas concentrations in the atmosphere combined with increased infrared radiation (e.g., due to reflective snow and ice melting exposing dark oceans that absorb solar radiation and reemit it as infrared radiation) causes even faster heating, such as is happening in the arctic.

Some skeptics point to Snowball Earth to “prove” that CO2 does not cause warming, by noting that 650 million years ago CO2 concentrations exceeded 1000 ppm yet the world was frozen solid, even down to the equator. Part of what allowed Snowball Earth to occur was because solar radiation was 4% lower than today, but a major reason that Snowball Earth persisted for so long is that snow and ice reflect 90% of incoming solar radiation, reducing infrared radiation to the point that the greenhouse effect was severely reduced.

Snowball and Dirtball Earth Radiation Balances

Snowball and Dirtball Earth radiation balance (graphics by jg).



Handy resources when facing a firehose of falsehoods

Posted on 3 May 2016 by BaerbelW

Chances are high that you will have come across somebody somewhere on the internet who still doesn't accept the overwhelming scientific consensus on human-caused global warming. That somebody may well have used a veritable firehose of falsehoods - usually referred to as a gish-gallop - where a big list of myths is fired off in quick succession. Creating such a gish-gallop is quick & easy and the urge to try and debunk all the misinformation it contains is often quite strong, but it's also a very time-consuming task to undertake. One time-saving option to tackle it, is to just concentrate on the most egregious instances of misinformation as examples of how the writer tries to mislead his readers and to ignore the rest. But, this has the disadvantage that others might accuse you of cherry-picking what you chose to debunk.

So, what other options do you have to fairly quickly dispense with such a firehose of falsehoods?

Option #1 - The Fact-Myth-Fallacy overview

Our MOOC Denial101x debunked around 50 of the most often heard myths related to climate science using the recipe to start out with the fact, followed by a short mention of the myth (with a warning!) and finishing off with explaining the fallacy employed. A condensed version of these debunkings is available as a four-page-PDF which you can download from here:

Fact-Myth-FallacyThe fallacies are based on the five techniques used by science deniers to distort facts: fake experts, logical fallacies, impossible expectations, cherry picking evidence, and conspiracy theories. The acronym FLICC is an easy way to remember these techniques.

FLICC: Fake experts, Logical fallacies, Impossible expectations, Cherry picking, Conspiracy theories. John Cook



Volcanic vs. Human-Caused CO2 Emissions - Updated Graphic

Posted on 8 September 2015 by jg

I create illustrations for authors of Skeptical Science posts, but lately I've had a hiatus of this activity. Some may even call it a pause, or a trend reversal. Others, however, know that there never was a pause, that the time I would have spent illustrating posts was absorbed in the deep ocean of our contribution to Denial101x. I'll be releasing some of these sequestered illustrations in our climate graphics section.

The first is a rework of our volcanic vs. human-caused emissions sketch, which appeared in "Message from the Past" by SKS author Peter Jacobs (See Denial101x Our comparison of volcanic to anthropogenic emissions summarized Gerlach 2011 (see EOS 14 June 2011), which estimated the ratio of human emissions to volcanic at 130 to 1. Though the clouds in my drawing were metaphors, I aimed for eye-ball accuracy by drawing 131 boxes:

Let me count the squares



How we know the greenhouse effect isn't saturated

Posted on 13 February 2014 by Glenn Tamblyn

This is the Basic rebuttal to the myth 'CO2 effect is saturated'

The mistaken idea that the Greenhouse Effect is 'saturated', that adding more CO2 will have virtually no effect, is based on a simple misunderstanding of how the Greenhouse Effect works.

The myth goes something like this:

  • CO2 absorbs nearly all the Infrared (heat) radiation leaving the Earth's surface that it can absorb. True!
  • Therefore adding more CO2 won't absorb much more IR radiation at the surface. True!
  • Therefore adding more CO2 can't cause more warming. FALSE!!!

Here's why; it ignores the very simplest arithmetic.

If the air is only absorbing heat from the surface then the air should just keep getting hotter and hotter. By now the Earth should be a cinder from all that absorbed heat. But not too surprisingly, it isn't! What are we missing?

The air doesn't just absorb heat, it also loses it as well! The atmosphere isn't just absorbing IR Radiation (heat) from the surface. It is also radiating IR Radiation (heat) to Space. If these two heat flows are in balance, the atmosphere doesn't warm or cool - it stays the same.

Lets think about a simple analogy:



Talking Trash on Emissions

Posted on 7 January 2014 by jg

While attending the recent AGU conference, some of us were struck by a statistic presented by Professor Richard Alley: On average, a person's contribution of carbon dioxide waste to the atmosphere is forty times greater than their production of solid trash to landfills when measured as mass.

It can be difficult to grasp the huge quantities of CO2 that we emit. It’s an invisible gas with no odour and we are not used to thinking about amounts of gas in terms of mass. But we do have a good sense of how much solid waste we throw out, since we all have to lug our garbage to the curb. If we had to do the same with our greenhouse gases, instead of one can a week, we would have to haul forty.

Every time we see a garbage truck, let’s imagine forty others following it, all taking our carbon dioxide to a dump site. When we hear of municipal politicians struggling to find new landfill sites, imagine the problems we would have finding forty subterranean landfill sites if we ever tried to dispose of our CO2 in the subsurface instead of dumping it freely into the air.



Behind the Lines: Herschel's Discovery of Infra-Red

Posted on 11 December 2013 by jg

As I study climate science, I draw pictures—my way of taking notes. At first, these illustrations were for myself, but with help from Skeptical Science authors, I've created many that are now in our climate graphics resources:

As with all our resources, these images are available to anyone to republish under our creative commons license. I will be adding to these, and when an image has a story of discovery behind it, I'll share it as a look behind the lines.

Behind the lines with Herschel's Discovery

A recent illustrated project is our interactive climate history timeline, based on a post by John Mason and converted into it's interactive format by Paul D., with editing by Paul and Baerbel. I created the icons and some of the illustrations that accompany various passages. One of the first (in time sequence) summarizes Herschel's discovery of infra-red:

Figure: Depiction of Herschel's discovery of infra-red light

Herschel's objective was to measure the temperature of the different wavelengths of light revealed by a prism. I had a mental image of the experiment from textbooks: Light source, prism, rainbow colors, and a very dignified Herschel. First decision: get rid of Herschel so I could finish the illustration within my deadline.

Second, confirm that I was placing the surviving elements, sun (light source), prism, light rays, in a defensible orientation:

I like to personally verify details in a drawing, when possible. I had no trouble finding a prism among my astro-junk (acquired from years of astronomy outreach), and used it to examine the relative position of the light scattering:

Prism splitting sunlight



The Dirt on Climate

Posted on 2 January 2013 by jg

Hao et al.* (Nature, 18 Oct 2012) has provided an estimate of the duration of Northern Hemisphere glaciations by digging into wind-blown dust deposits, called loess (pronounced "luss"). This work improves our understanding of the timing of the rise and fall of Arctic ice sheets over the past 900,000 years and provides evidence that our current interglacial, the Holocene, could have continued for another 40,000 years, even without an increase in greenhouse gases.

Humanity's industry has interrupted the Holocene, rendering moot the question of how long the Holocene would have lasted, but understanding what we are about to interrupt may help restore our conservative side—conservative in the sense of wanting to keep what we have.

What type of climate have we interrupted? Early climate science suggested that due to Earth's response to variations in orbit, Earth could be transitioning into the next ice age. Recent studies have the advantage of palaeoclimate reconstructions, such as this one based on 57 ocean sediment cores (Lisiecki and Raymo, Paleooceanography 2005), allowing us a better look at past climates:

Illustration of marine isotope stages, global temperatures and extended onset of N.H. glaciation from Hao et al.
Figure 1: From  Lisiecki and Raymo 2005, a comparison of global temperatures based on changes in 18O in ocean sediments with marine isotope stages inferred from this record. The adjustment to MIS 10 and 11 is from Hao et al. More data extending to 1 million years ago are available as a larger image.  Click the figure to see the larger image.



Uncertainty Is Not the Basis for Investment

Posted on 22 February 2012 by jg

Warren Meyers, writing in Forbes magazine (Forbes 2/9/12), argues that breaking the theory of AGW into three parts undermines the potency of the often cited 97% consensus (Science, 03 December 2004):

Part 1) doubling CO2 induces global warming of 1 degree C.
Part 2) CO2-based warming will be amplified by feedback effects.
Part 3) the results will be bad for civilization.

Meyers argues that the 97% consensus is valid for part 1, but breaks down when parts 2 and 3 stand apart. Yet, his support for this censensus breakdown diverges from what a careful reading of the climate change literature would offer. He also takes on the more difficult position of proving negatives, and so additional information from the peer-reviewed literature should move his conclusions toward the conservative direction. (By "conservative," I mean, if you have a mild interglacial that has been conducive to civilization and prosperity, don't mess with it.)

Before celebrating our agreement on Part 1, it should be noted that 1C per doubling of atmospheric CO2 may be an underestimate and that 1.2 C may be more accurate (Hansen and Sato). Whether the value is 1 or 1.2, this is no small change for two reasons:



DenialGate - Infographic Illustrating the Heartland Denial Funding Machine

Posted on 18 February 2012 by dana1981

Note: the graphic below was updated at at 16:35 PM on 18 February 2012 to correct a couple of minor errors.  A portion of the government relations budget had been double-counted, and some of the Heartland proposed budgetary figures extend beyond 2012.  See the discussion below for further details.

*update* the graphic was updated again on 23 Feb 2012 to remove the Charles Koch Industries $225k donation.  The foundation donated $25k to Heartland in 2011 for health care research, but will not make Heartland's expected $200k 2012 donation.

*update 2* the graphic was updated again on 24 Feb 2012 to remove David Watkins' name.  Watkins relayed the following message to Skeptical Science:

"David Watkins has had no relationship with the Heartland Institute.  He has not accepted (nor has he been offered) any funds from them.  He is not a supporter of the Nongovernmental International Panel on Climate Change, and in fact he routinely uses results from reports of the Intergovernmental Panel on Climate Change in his research on water resources adaptation planning for climate change."

Skeptical Science's resident artist (that's pronounced "ar-teest") jg has put together an infographic illustrating the Heartland Institute's funding sources and planned budget payments (based on lots of input and suggestions from the whole Skeptical Science team; click the image for a hi-rez version):

heartland funding infographic



The Last Interglacial Part Five - A Crystal Ball?

Posted on 17 November 2011 by Steve Brown

Note: This is the fifth and final article of a five-part series on what we can learn from the Last Interglacial time period. Understanding this period may provide clues on how the environment may respond to similar conditions in the future. In the first post, we described the conditions that exisited during the Last Interglacial. In the second post, we looked at the key factors for making it a warm period. In the third post, we looked at how sea-levels rose as a result of melting ice-sheets.  In the fourth post, we examined how the Last Interglacial oceans influenced the climate.  In this final post, we summarise what we've learnt and conclude the discussion on the value of the Last Interglacial for helping us predict the future.

Comparing the influences on the Last Interglacial climate with those assumed in future climate projections is problematic owing to fundamental differences, especially orbital forcing, seasonal warming, and greenhouse gas concentrations.  Palaeoclimate studies show that differences in the manner in which the Earth orbited the Sun during the Last Interglacial are sufficient to explain the higher temperatures over most parts of the Northern Hemisphere, particularly due to greater axial tilt and eccentricity compared with the present day orbital configuration.  This greater axial tilt provided stronger insolation (solar heating) at high latitudes and weaker insolation at low latitudes.  Perihelion, when the Earth is nearest the Sun, occurred during summer in the Northern Hemisphere, which amplified seasonal insolation, while perihelion occurs in winter during the present day.  Figure 1 shows a comparison of Eemian and Holocene summer insolation, which highlights the key differences between then and now.  If you click on Figure 1, it will show an animation to make this easier to visualise.  Peak insolation from orbital forcing will be significantly lower over the next century than what the Earth received during the peak warm period around 126,000 years ago.

Comparison of Eemian and Holocene Summer Insolation

Figure 1: Comparison of Eemian and Holocene Summer Insolation - click for animation (Illustration and animation by jg)



The Last Interglacial Part Three - Melting Ice and Rising Seas

Posted on 10 August 2011 by Steve Brown

NOTE: This is the third article of a five-part series on what we can learn from the Last Interglacial time period. Understanding this period may provide clues on how the environment may respond to similar conditions in the future. In the first post, we described the conditions that exisited during the Last Interglacial. In the second post, we looked at the key factors for making it a warm period. In this post, we examine two of the most profound environmental impacts that resulted from the warm climate.

In the previous posts we learned that the Last Interglacial, also known as the Eemian in Europe, was significantly warmer than today in large regions of the Northern Hemisphere, and may have been around 1oC warmer globally.  The main reason for this warmer climate was an increased amount of energy from the Sun being received at high northern latitudes due to Earth's orbital configuration, plus Earth had an increased capacity to absorb heat due to vegetation changes and reduced ice and snow cover.  The period is also known for global sea level being several metres higher than today.  So how high did sea levels get and why?

Contrary to what common sense might tell you, global sea-level is not the same everywhere and can vary by many metres from region to region.  Seawater can bulge up in regions under local gravitational influence due to proximity of land masses, undersea mountains, or even due to changes in atmospheric pressure.  Physical properties of the sea water such as temperature and salinity will affect its density and hence the volume it occupies.  Sea level also depends on the actual amount of water in the oceans, which can be altered significantly during the course of glacial/interglacial cycles depending on the mass of water locked up in glaciers and ice-sheets.

The IPCC AR4 report describes evidence from a variety of sources that suggests either a partial or a complete disappearance of the Greenland Ice Sheet during the Last Interglacial, providing a contribution of 2 to 4 m of sea-level rise.  This was likely over a period of several thousand years in conjunction with an Arctic summer warming of up to +5oC.   There is uncertainty in the interpretation of Greenland ice core records, though it does seem likely that the Greenland Ice Sheet lost at least half of its volume and the top of the ice sheet in the Summit region may have been 500 m lower than the present day.   Otto-Bliesner et al. (2006) simulated the behaviour of the Greenland Ice Sheet in response to the known climate forcings of the Last Interglacial.  They found ice melt configurations consistent with palaeo-records of the Greenland environment, which suggest a sea-level rise contribution of 2.2 m to 3.4 m (Figure 1).  The Greenland Ice Sheet melt is very sensitive to warm summers, which is what resulted from the particular orbital forcing configuration of the Last Interglacial.

Last Interglacial Greenland Ice Sheet Simulation

Figure 1: Simulated Greenland Ice Sheet thickness maps.  Configuration A gives a minimum sea-level contribution of 2.2 m.  Configuration B gives a maximum sea-level rise of 3.4 m likely contributed by the Arctic. (Otto-Bliesner et al. 2006)



Ice data made cooler

Posted on 9 December 2010 by jg

Guest post by John Garrett

I am an illustrator who started studying the primary scientific literature to better understand what I thought was a controversy over global warming. I quickly learned that climate science was not an island surrounded by controversy, but a well-founded continent, and most critics I met were merely poor navigators. To point them toward land, I created an interactive Vostok viewer, a Flash program that provides simultaneous displays of temperature, greenhouse gases, incident solar radiation (insolation), and Earth's eccentricity, tilt, and climatic precession for the span of the Vostok ice core.



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