Most people have a firm opinion on whether human emissions of carbon dioxide (CO2) are causing unnatural global warming and hold that opinion without understanding how the molecule physically absorbs and then releases heat energy.
Understanding that mechanism reveals why today’s significant global CO2 emissions are insignificant to future global warming.
Analogies are a great way to explain science, and I’m going to share the worst and best analogies for how carbon dioxide acts as a greenhouse gas. I will also share why the warming effect of CO2 is limited.
Two Very Bad Analogies
The NASA website for kids contains an illustration of a greenhouse with plants growing on the inside and a snowman on the outside.
The caption is: “The greenhouse effect works much the same way on Earth. Gases in the atmosphere, such as carbon dioxide, trap heat similar to the glass roof of a greenhouse.”
Former U.S. Secretary of State John Kerry described greenhouse gases as a thin layer of gases that acts as a blanket at the edge of our atmosphere and works “exactly like a greenhouse.”
Both of these analogies are terrible because the Earth’s atmosphere is not like a greenhouse roof.
Let’s look at the energy the sun sends to the Earth. The sun emits short-wave radiation that warms the surface of the Earth.
Seventy percent of that energy is then carried to the upper atmosphere by evaporation and convection (think of thunderhead clouds forming) and then radiated to space.
The remaining 30% escapes to space by long-wave infrared radiation (think of heat coming off a toaster). Every day new energy from the sun warms the surface of the Earth and an equal amount escapes back to space.
A greenhouse roof allows the short-wave sunlight in and the long-wave infrared radiation out but blocks the energy loss caused by convection and evaporation.
Greenhouse gases in the atmosphere work exactly the opposite; they allow heat loss from the surface by evaporation and convection and absorb some of the long-wave infrared radiation.
Each of the greenhouse gases absorbs specific wavelengths of infrared radiation and then re-emits that radiation in all directions.
Some of that is directed back towards the surface of the Earth where it is again absorbed and again released. This recycling of heat is the greenhouse gas effect, and it’s nothing like a heat-trapping roof except for the deceptive name.
CO2 absorbs infrared radiation of wavelengths between 14 and 16.5 microns. To understand the scale: it would take about five of these wavelengths laid end to end to equal the diameter of a human hair.
Adding more CO2 means more of these infrared wavelengths can be absorbed. But more CO2 does not mean a proportionately similar increase in recycled heat.
It’s because the Earth radiates a limited amount of those specific wavelengths of heat that CO2 can absorb.
Two Much Better Analogies
Dr. Ian Plimer wrote in Heaven and Earth that “Carbon dioxide in the atmosphere operates like a curtain on a window. If you want to keep out light, add a curtain. A second curtain makes little difference, a third curtain makes even less difference, and a fourth curtain is totally ineffectual.”
In his book Unsettled, Dr. Steven Koonin uses a similar analogy that the first few molecules of CO2 in the atmosphere are “…like the first layer of black paint on a clear window.”
He further states that doubling the CO2 concentration from today’s approximately 400 parts per million “doesn’t change things much … due to the ‘painting a black window effect.’”
These analogies are much better as they convey the concept (but without the mathematics) that once you have blocked all the available CO2-specific radiation, more blockage has no further effect.
My Analogy
In my book, I wrote that CO2 is like multiple fish weirs, each placed partially across a river with salmon swimming upstream.
The first weir catches a lot of fish, but it takes two more weirs upstream of the first to catch the same number of fish as the first, and then four more further upstream to again catch the same amount as the first weir. This happens because the river is being depleted of salmon.
My analogy exemplifies the Arrhenius greenhouse gas theory, which is accepted by the Intergovernmental Panel on Climate Change (IPCC).
The theory states that if all the CO2 emitted by humans since the start of the industrial revolution caused 1°C of global warming, it would take twice that volume to cause the next 1°C of warming and four times that initial volume for the third 1°C of warming.
This happens because the Earth’s 14 to 16.5-micron infrared radiation is being depleted.
That’s the math, but it still doesn’t explain how the CO2 molecule physically absorbs and then releases long-wave infrared radiation.
The Best Analogy
Dr. William Happer compares infrared radiation striking a CO2 molecule to a mallet striking a xylophone bar.
A xylophone bar is loosely attached to the frame near its two ends and when it is struck by a mallet in the middle, the mechanical energy absorbed causes the bar to vibrate and then is released as sound energy in all directions.
A carbon dioxide molecule consists of a carbon atom held loosely in a straight line on both sides by oxygen atoms. When it is struck by infrared radiation the molecule absorbs the energy by deflecting the two oxygen atoms off of the straight line and reradiates the energy when the molecule springs back to a straight line.
A simplified view looks like this (from University Corporation for Atmospheric Research):
Because the whole molecule is spinning in multiple directions, the reradiation is sent in all directions. But only certain wavelengths of energy can act as the xylophone mallet: 14 to 16.5 microns.
Dr. Happer has pointed out that the diagram above is simplified because in the one second it takes for the CO2 molecule to release the energy, it could have up to a billion collisions with other air molecules and transfer the energy to them before it can be released as longwave infrared energy.
Why Today’s Carbon Dioxide Emissions Are Insignificant to Global Warming
As more CO2 molecules are added as potential absorbers for the fixed amount of the specific band of infrared radiation, there is less chance that any CO2 molecule will be hit. If the additional CO2 molecules do not absorb infrared radiation, they cannot contribute to global warming.
The ever-reducing CO2 contribution to global warming looks like this graph, which, ironically, is based on the IPCC’s formula (from Inconvenient Facts by Gregory Wrightstone):
On the graph above, consider that the pre-industrial (circa 1875) atmospheric CO2 level was about 280 parts per million (ppm), and today it is about 420 ppm—an increase of 140 ppm.
As a rough approximation, the three bars labeled 350, 400, and 450 ppm represent this past increase in CO2, and the sum of the global warming temperature increases associated with those three bars is about 0.7°C.
The next four bars (500, 550, 600, and 650 ppm) represent a future CO2 increase of 200 ppm, which at today’s rate of 2.5 ppm increase each year would take from now to about 2100.
The global warming associated with those four bars is only 0.65°C. The graph shows it keeps taking more CO2 to achieve a smaller amount of global warming.
I chose bars 350 through 650 ppm to highlight that the IPCC’s formula predicts that global warming from current CO2 emissions held flat (1.35°C) would still beat the IPCC’s target of 1.5°C of human-caused global warming from preindustrial times to the year 2100.
The above graph suggests global warming from increasing CO2 never stops, but we know from ancient climates that even 12 times today’s CO2 concentrations did not cause runaway global warming.
Drs. Happer, Koonin, and Lindzen submitted to the U.S. (Northern California) District Court in 2021 that minor changes in cloud cover and convection currents can have a bigger effect on the Earth’s surface temperature than major increases in CO2.
This is because CO2 is well mixed throughout the entire 80-kilometer thickness of the atmosphere. As more CO2 is added, the chances of long-wave infrared radiation re-emitted by a CO2 molecule reaching the surface of the Earth are greatly reduced because it is likely to be absorbed by another CO2 molecule closer to the Earth.
That lower altitude CO2 molecule would most probably lose that extra energy in a collision with another air molecule and promote more air convection currents to the upper atmosphere.
Happer, Koonin, and Lindzen submitted that at today’s concentration, only CO2 molecules a few hundred meters above the ground re-emit long-wave infrared radiation that makes it back to the surface of the Earth.
Future CO2 emissions will result in little or no global warming because there is a limited supply of the 14- to 16.5-micron infrared radiation to absorb, and the new emissions will be well mixed in the atmosphere, most too far above the Earth to cause surface warming.
The CO2 molecule is like a xylophone bar but is only activated by specific wavelengths of heat. Then like sound, that energy is sent in all directions.
Note to NASA and John Kerry: That’s nothing like a greenhouse roof.
Ron Barmby (www.ronaldbarmby.ca) is a Professional Engineer with a Bachelor’s and Master’s degree, whose 40+ year career in the energy sector has taken him to over 40 countries on five continents. His book, Sunlight on Climate Change: A Heretic’s Guide to Global Climate Hysteria (Amazon, Barnes & Noble), explains in layman’s terms the science of how natural and human-caused global warming work.
Ennyi zagyvaságot, egyoldalú szemléletet még nem olvastam előadóktól és hozzászólóktól! Senki nem tájékozódott a klímaváltozás összetettségével kapcsolatban, Ha az összes változatos hozzászólásba csak beleolvasnak, nem jegyeznek be ilyen egyoldalú- egysíkú süketséget, ami a gondolkodás nélküli tovább szajkózását tükrözi és osszák az észt az agyontanult okostojások. Szégyen, hogy ebben a témában ilyen nagy tudású emberek részt vesznek gátlástalanul!
The salmon weir analogy is so easy to grasp but I appreciate also having a more detailed explanation of how heat is held or released from our atmosphere. Great article!
Jane;
Thank you!
“Every day new energy from the sun warms the surface of the Earth and an equal amount escapes back to space.”
If that statement had been true, the average temperature of our planet would never change. In fact, it is always changing. Only a fool would make such a false statement. Not a person who can be taken seriously on the subject of climate science. And we don’t need analogies about CO2. We have the results of laboratory spectroscopy and actual experience with global warming from 1975 to 2015. There is no need for analogies when we have real measurements and real observations, by over 7 billion people, of actual global warming. We don’t need analogies or climate predictions — we need measurements and data of what actually happened as CO2 increased.
Short answer: Our planet’s climate became more moderate and green plants grew faster. More CO2 in the atmosphere would be even more good news.
I happen to be one of the 7 billion observers that you mention and I have been observing the climate of this planet for three quarters of a century and as yet I have not noticed any change in weather or climate!
John,
It is happening so slowly that it is not noticible. A 1.1C to 1.3C increase since 1850 seems reasonable to me (based on literature searches of the research). That could be mostly natural climate change due to the end of the Little Ice Age. Satellite measurements indicate a 40 year trend of about 0.1C per decade. 2022 did not reach the modern global average temperature set in the el Nino year of 1998, which I contend translates to 24 years of no current global warming, or at a minimum no climate emergency.
Richard;
The greenhouse gas effect is in equilibrium (Sun’s energy in = Earth’s energy out). It can be re-set to a new equilibrium (a higher average global temperature) if there is low CO2 in the atmosphere and that is increased significantly, but above 400 ppm the experts I quoted don’t think it will have much effect due to the saturtion effect of CO2 in the atmosphere. That does not mean the energy from the sun absorbed by the Earth’s surface is constant. We have observed at least two correlations where reduced energy recieved from the sun corresponds with climate change. The first is a the long term Milankovitch cycle of the Earths orbit changing its eliptical path; every 100,000 years we orbit furthest from the sun and recieve less energy. This corresponds to 100,000 year cycles of glaciation. The second is the magnetic field of the sun effects cloudiness on Earth. A weak sun enables more low-level and denser clouds to form, which significantly blocks sunlight from reaching the surface. During the Little Ice age there were 5 consecutive Grand Solar Minimums, and the Little Ice Age ended in the late 19th century with the Modern Solar Maximum. We don’t know how cloudy it was during the Little Ice Age compared to the 20th centrury, but we know the sun’s magnetic field was weaker.
The greenhouse gas effect is in enegy equilibrium, but the amount of energy the surface of the Earth receives from the sun is not constant. This corellates resonably well with natural climate change. Correlation is not proof, but it is evidence to consider.
“Every day new energy from the sun warms the surface of the Earth and an equal amount escapes back to space.” He is correct here Solar climate forcing is relatively stable compared to other forcing like stochastic activity which is more random. The Pacifics Ring of Fire in comparison has app.3000 submarine volcanoes that we know of (most likely a few thousand more that we aren’t aware of) emitting CO2 as well as aerosols which actually have an atmospheric cooling effect. They generate the heat in the Ocean that powers El Niño-Southern Oscillation (ENSO) climate pattern. We know little about our vast Oceans which cover 70%+ of Earth’s surface and not much more about their effect on planetary climate patterns. One thing is certain, no matter how many parts per million man have historically contributed to overall atmospheric CO2 content, the effect on the climate compared to natural forcing is infinitesimal at best.
Brian;
Thank you! Sub-sea (plus sub-ice) volcanoes are a big unkown.