We've reached a turning point where it is hard for any Global Warming Alarmist to claim (with a straight face) that the world as we know it is about to end in a decade or two or three unless we stop burning fossil fuels. Anyone deluded or foolish enough to make such a claim would be laughed at by many audiences.
GLOBAL WARMING IS REAL
Yes, the world has warmed 1°F to 1.5°F (0.6°C to 0.8°C) since 1880 when relatively good thermometers became available. Yes, part of that warming is due to human activities, mainly burning unprecedented quantities of fossil fuels that continue to drive an increase in carbon dioxide (CO2) levels. The Atmospheric "Greenhouse" Effect is a scientific fact!
BUT GLOBAL WARMING IS NOT A BIG DEAL
As the animated graphic clearly indicates, the theoretical climate models used by the Intergovernmental Panel on Climate Change (IPCC) are handcuffed to inordinately high estimates of climate sensitivity (how much temperatures are expected to rise given a doubling of CO2). Since the advent of good satellite-based global temperature data in 1979, observed temperatures have risen at a fraction of the IPCC predicted rate even as CO2 continues to rise. Relax, there is not and never has been any near-term "tipping point". The actual Earth Climate System is far less sensitive to CO2 than claimed the IPCC climate theory, as represented by their computer models. Global Warming since 1880 is mainly due to Natural Cycles and Processes not under human control. Yes, the same Natural Cycles and Processes that were responsible for the many Ice Age cycles that repeatedly occurred about every 100,000 years or so.
MY JANUARY 2014 PRESENTATION
By a stroke of good fortune, last week I was scheduled to present "Visualizing the Atmospheric 'Greenhouse' Effect - Global warming is real, but how much is due to human activities and how big is the risk?" to the Philosophy Club in the Central Florida retirement community where I live. This is a great time for Global Warming Skeptics to put the Alarmists in their place.
Everyone in the highly interactive and supportive audience was aware of newspaper and TV reports of the drama of those ill-fated Global Warming "Research" activists whose Russian ship, the Academik Shokalskiy, got stuck in the summer ice of the Antarctic. (Fortunately, those people are safe, having been rescued by a helicopter from a Chinese icebreaker.) In addition to the Antarctic adventure gone wrong, in the week leading up to and following my talk, the media was overrun by stories of the "polar vortex" literally freezing large parts of the US and even causing Florida temperatures to drop below 30°F.
Of course, we realize that the cold wave is only anecdotal evidence and "weather is not climate". However, photos and videos of researchers stuck in the Antarctic summer ice as well as scenes of American life frozen in place for days on end, when combined with clear and irrefutable evidence of a slowdown in warming since 1979 and no statistically significant warming since 1996 (as depicted in the graphic above), has considerable emotional impact.
My animated PowerPoint Show, which should run on any Windows PC, is available for download here. (NOTE: I knew that many members of The Philosophy Club audience, while highly intelligent and informed, are not particularly scientifically astute. Therefore, I kept to the basics and invited questions as I proceeded. Since most of them think in Fahrenheit, I was careful to give temperatures in that system. By contrast, my 2011 talk to the more scientifically astute members of our local Science and Technology Club Skeptic Strategy for Talking about Global Warming was more technical. Both presentations make use of animated PowerPoint charts and you are free to download and use them as you wish.)
My presentation is based on my five-part series for the most viewed climate website in the world, "Watts Up With That" (WUWT) where I am a Guest Contributor. The series is entitled "Visualizing the 'Greenhouse Effect'" - 1 - A Physical Analogy, 2 - Atmospheric Windows, 3 - Emission Spectra, 4 - Molecules and Photons, and 5 - Light and Heat. The series, which ran in 2011, generated tens of thousands of page views at WUWT, along with thousands of comments.
I wrote the series because WUWT is a "skeptic" website and attracts some viewers who reject the basic physics of the Atmospheric "Greenhouse" Effect. (The owner of WUWT, Anthony Watts, like me, accepts the basic physics and the fact that some of the warming of the past century is indeed due to human activities, such as unprecedented burning of fossil fuels that have raised CO2 levels. However, we are skeptical about how much the Earth Surface has actually warmed, and how big a risk is posed by moderate increases in CO2 and temperature.)
HOW A REAL GREENHOUSE WORKS
I explained how a real physical Greenhouse works and how that is both similar and different from the Atmospheric "Greenhouse" Effect. The Greenhouse descriptions I learned in high school, as well as those available on the Internet, consider only the RADIATIVE effect. The glass roof of the Greenhouse allows visible light to pass through freely, heating the soil, plants, and air, but is opaque to the resultant infrared radiation, which is partly re-radiated back down into the Greenhouse, warming it further. That part is true, but far from the whole story. The MAIN reason a Greenhouse stays warm is that it is airtight to restrict CONVECTION and it is insulated to restrict CONDUCTION. In fact, it is possible to construct a successful Greenhouse using a roof made from materials that allow both visible and infrared to pass freely, but is impossible to make a working Greenhouse that is not both airtight and insulated.
HOW THE ATMOSPHERIC "GREENHOUSE" EFFECT WORKS
All warm objects emit radiation at a wavelength dependent upon the temperature of the object. The Sun, at around 10,000 °F, emits "short-wavelength" infrared radiation, centered around 1/2 micron (one millionth of a meter). The soil, plants, and air in the Greenhouse, at around 60 to 100 °F, emit "long wavelength" radiation, centered around 10 microns (with most of the energy between 4 and 25 microns).
The Atmospheric "Greenhouse" Effect works because:
- Short-wavelength radiation from the Sun passes freely through the gases that make up the Atmosphere,
- About a third of this Sunlight is reflected back by white clouds, dust, and light-colored objects on the Surface, and that energy is lost to Space,
- The remaining two-thirds of the Sunlight energy is absorbed by the Sea and Land Surface and causes it to warm,
- The warm Surface cools by emitting long-wavelength radiation at the Bottom of the Atmosphere, and this radiation passes towards the Top of the Atmosphere, where it is ultimately lost to Space,
- On the way to the Top of the Atmosphere, much of this radiation is absorbed by so-called "Greenhouse" gases (mostly water vapor and carbon dioxide) which causes the Atmosphere to warm,
- The warmed Atmosphere emits infrared radiation in all directions, some into Space where it is lost, and some back towards the Surface where it is once again absorbed and further warms the Surface.
- In addition to the RADIATIVE effects noted in points 1 through 6, the Surface is cooled by CONVECTION and CONDUCTION (thunderstorms, winds, rain, etc.)
If not for the warming effect of "Greenhouse" gases, the Surface of the Earth would average about -1 °F, which would prevent life as we know it. This effect is responsible for about 60 degrees F of warming.
According to the Intergovernmental Panel on Climate Change (IPCC), the Earth Surface has warmed about 1.5 °F since good thermometer data became available around 1880. Some skeptics (including me) believe the actual warming is closer to 1 °F, and that government agencies have adjusted the thermometer record to exaggerate the warming by 30% or more.
However, it doesn't really matter whether the actual warming is 1 °F or 1.5 °F because we are arguing about only 0.5 °F, which is less than 1% of the warming due to the Atmospheric "Greenhouse" Effect.
HOW SENSITIVE IS THE CLIMATE TO HUMAN ACTIVITIES?
The IPCC claims that the majority of the warming since 1880 is due to human activities. It is true that we are burning unprecedented amounts of fossil fuel (coal, oil, gas), and that we are making land use changes that may reduce the albedo (reflectiveness) of the Surface. Most of the increase in Atmospheric CO2 (a 40% rise from about 270 to nearly 400 parts per million by volume) is due to human activities.
The IPCC claims that Climate Sensitivity (the average increase in Surface temperatures due to a doubling of CO2) is between 3 °F and 8 °F. Some skeptics (including me) believe they are off by at least a factor of two, and possibly a factor of three, and that Climate Sensitivity is closer to 1 °F to 3 °F.
As evidence for our conclusions, we point to the fact that virtually ALL of the IPCC climate models have consistently over-estimated future temperature predictions as compared to the actual temperature record. Indeed, for the past 17 years as CO2 levels continue their rapid climb, temperatures have leveled off, which is proof that Natural Cycles, not under human control or influence, have cancelled out warming due to CO2 increases. Thus, Natural Cycles must have a larger effect than CO2.
VISUALIZING THE ATMOSPHERIC "GREENHOUSE" EFFECT
As I noted above, I wrote the "Visualizing" series for WUWT (1 - A Physical Analogy, 2 - Atmospheric Windows, 3 - Emission Spectra, 4 - Molecules and Photons, and 5 - Light and Heat) because some WUWT viewers are "Disbelievers" who have had an "equal and opposite" reaction to the "end of the world" excesses of the Global Warming "Alarmists". By failing to understand and accept the basic science of the Atmospheric "Greenhouse" Effect, they have, IMHO, "thrown the baby out with the bathwater".
1 - A Physical Analogy
Albert Einstein was a great theoretical physicist, with all the requisite mathematical tools. However, he rejected purely mathematical abstraction and resorted to physical analogy for his most basic insights. For example, he imagined a man in a closed elevator being transported to space far from any external mass and then subjected to accelerating speeds. That man could not tell the difference between gravity on Earth and acceleration in space, thus, concluded Einstein, gravity and acceleration are equivalent, which is the cornerstone of his theory of relativity. Einstein never fully bought into the mainstream interpretation of quantum mechanics that he and others have called quantum weirdness and spooky action at a distance. He had trouble accepting a theory that did not comport with anything he considered a reasonable physical analogy!
So, if you have trouble accepting the atmospheric “greenhouse” effect because of the lack of a good physical analogy, you are in fine company.
Well, getting back to the Atmospheric "Greenhouse Effect, a "disbelieving" commenter on WUWT, suggested we think of the Sunlight as truckloads of energy going from the Sun to the Earth Surface, and the infrared radiation from the Surface as equal truckloads going the other way. How, he asked, could these equal and opposite truckloads do anything but cancel each other out as far as the amount of energy on the Surface of the Earth? In reply, I posted a comment with an analogy of truckloads of orange juice, representing short-wave radiation from Sun to Earth, and truckloads of blueberry juice, representing longwave radiation between Earth and the Atmosphere and back out to Space.
That thought experiment triggered my creativity. I imagined the Sun as a ball-pitching machine, throwing Yellow balls towards the "Earth" Surface (representing short-wave radiation) and Purple balls (representing long-wave radiation) bouncing back towards Space and interacting with the Atmosphere. The graphic below is one of my depictions of the physical analogy. Follow this link for more graphics and detail.
I imagined the Earth as a well-damped scale. The Yellow balls would bounce off the Surface and turn into Purple balls (representing long-wave radiation as the Earth absorbed the short-wave radiation and then emitted an equal quantity of long-wave radiation). The scale would read "1" unit.
If there was no Atmosphere, or if the Atmosphere contained no "Greenhouse" gases to obstruct the flight of the Purple balls, they would fly out towards Space.
I then imagined the Atmosphere as an obstacle that absorbed the Purple balls, split them in two, and emitted half of the smaller balls to Space and the other half back towards the Earth. The balls going towards Earth would be absorbed, further heating the Earth, and the warmed Earth would emit them back towards the Atmosphere. The process would be repeated with the balls being absorbed by "Greenhouse" gases in the Atmosphere, and then emitted with half going out to Space, and half back to the Earth. The sum of 1 + 1/2 + 1/4 + 1/8 +1/16 ... = 2 (approximately), so the scale reads "2" units.
Thus, in my simplified analogy, the "Greenhouse" gases in the "Atmosphere" cause the scale reading to double. So, the Atmospheric "Greenhouse" Effect causes the Earth Surface to be warmer than it would be absent the "Greenhouse" gases. I think Einstein would be pleased! Read more detail at WUWT, including the 340 responses (comments received and my brilliant replies!)...,
2 - Atmospheric Windows
A real greenhouse has windows. So does the Atmospheric “greenhouse effect”. They are similar in that they allow Sunlight in and restrict the outward flow of thermal energy. However, they differ in the mechanism. A real greenhouse primarily restricts heat escape by preventing convection while the “greenhouse effect” heats the Earth because “greenhouse gases” (GHG) absorb outgoing radiative energy and re-emit some of it back towards Earth.
There are two main “windows” in the Atmospheric “greenhouse effect”. The first, the Visible Light Window, on the left side of the graphic, allows visible and near-visible light from the Sun to pass through with small losses, and the second, the Longwave Window, on the right, allows the central portion of the longwave radiation band from the Earth to pass through with small losses, while absorbing and re-emitting the left and right portions.
Sunlight Energy In = Thermal Energy Out
The graphic is an animated depiction of the Atmospheric “greenhouse effect” process.
On the left side:
(1) Sunlight streams through the Atmosphere towards the surface of the Earth.
(2) A portion of the Sunlight is reflected by clouds and other high-albedo surfaces and heads back through the Atmosphere towards Space. The remainder is absorbed by the Surface of the Earth, warming it.
(3) The reflected portion is lost to Space.
On the right side:
(1) The warmed Earth emits longwave radiation towards the Atmosphere. According to the first graphic, above, this consists of thermal energy in all bands ~7μ, ~10μ, and ~15μ.
(2) The ~10μ portion passes through the Atmosphere with litttle loss. The ~7μ portion gets absorbed, primarily by H2O, and the 15μ portion gets absorbed, primarily by CO2 and H2O. The absorbed radiation heats the H2O and CO2 molecules and, at their higher energy states, they collide with the other molecules that make up the air, mostly nitrogen (N2), oxygen (O2), ozone (O3), and argon (A) and heat them by something like conduction. The molecules in the heated air emit radiation in random directions at all bands (~7μ, ~10μ, and ~15μ). The ~10μ photons pass, nearly unimpeded, in whatever direction they happen to be emitted, some going towards Space and some towards Earth. The ~7μ and ~15μ photons go off in all directions until they run into an H2O or CO2 molecule, and repeat the absorption and re-emittance process, or until they emerge from the Atmosphere or hit the surface of the Earth.
(3) The ~10μ photons that got a free-pass from the Earth through the Atmosphere emerge and their energy is lost to Space. The ~10μ photons generated by the heating of the air emerge from the top of the Atmosphere and their energy is lost to Space, or they impact the surface of the Earth and are re-absorbed. The ~7μ and ~15μ generated by the heating of the air also emerge from the top or bottom of the Atmosphere, but there are fewer of them because they keep getting absorbed and re-emitted, each time with some transfered to the central ~10μ portion of the longwave band.
the infrared (long-wavelength). Read more detail at WUWT, including the 489 responses (comments received and my brilliant replies!)...
3 - Emission Spectra
The Atmospheric “greenhouse effect” has been analogized to a blanket that insulates the Sun-warmed Earth and slows the rate of heat transmission, thus increasing mean temperatures above what they would be absent “greenhouse gases” (GHGs). Perhaps a better analogy would be an electric blanket that, in addition to its insulating properties, also emits thermal radiation both down and up. The graphic below, based upon actual measurements of long-wave radiation as measured by a satellite LOOKING DOWN from the Top of the Atmosphere as well as from the Surface LOOKING UP from the Bottom of the Atmmsphere, depicts the situation.
Description of graphic (from bottom to top):
Earth Surface: Warmed by shortwave (~1/2μ) radiation from the Sun, the surface emits upward radiation in the ~7μ, ~10μ, and ~15μ regions of the longwave band. This radiation approximates a smooth “blackbody” curve that peaks at the wavelength corresponding to the surface temperature.
Bottom of the Atmosphere: On its way out to Space, the radiation encounters the Atmosphere, in particular the GHGs, which absorb and re-emit radiation in the ~7μ and ~15μ regions in all directions. Most of the ~10μ radiation is allowed to pass through.
The lower violet/purple curve (adapted from figure 8.1 in Petty and based on measurements from the Tropical Pacific looking UP) indicates how the bottom of the Atmosphere re-emits selected portions back down towards the surface of the Earth. The dashed line represents a “blackbody” curve characteristic of 300ºK (equivalent to 27ºC or 80ºF). Note how the ~7μ and ~15μ regions approximate that curve, while much of the ~10μ region is not re-emitted downward.
“Greenhouse Gases”: The reason for the
Note that H2O absorbs at up to 100% in the ~7μ region. H2O also absorbs strongly in the ~15μ region, particularly above 20μ, where it reaches 100%. CO2 absorbs at up to 100% in the ~15μ region.
Neither H2O nor CO2 absorb strongly in the ~10μ region.
Since gases tend to re-emit most strongly at the same wavelength region where they absorb, the ~7μ and ~15μ are well-represented, while the ~10μ region is weaker.
Top of the Atmosphere: The upper violet/purple curve (adapted from figure 6.6 in Petty and based on satellite measurements from the Tropical Pacific looking DOWN) indicates how the top of the Atmosphere passes certain portions of radiation from the surface of the Earth out to Space and re-emits selected portions up towards Space. The dashed line represents a “blackbody” curve characteristic of 300ºK. Note that much of the ~10μ region approximates a 295ºK curve while the ~7μ region approximates a cooler 260ºK curve. The ~15μ region is more complicated. Part of it, from about 17μ and up approximates a 260ºK or 270ºK curve, but the region from about 14μ to 17μ has had quite a big bite taken out of it. Note how this bite corresponds roughly with the CO2 absorption spectrum.
See more graphics and detail at WUWT, including the 476 responses (comments received and my brilliant replies!)...
4 - Molecules and Photons
In this part, we consider the interaction between air molecules, including Nitrogen (N2), Oxygen (O2), Water Vapor (H2O) and Carbon Dioxide (CO2), with Photons of various wavelengths. This may help us visualize how energy, in the form of Photons radiated by the Sun and the Surface of the Earth, is absorbed and re-emited by Atmospheric molecules.
The animated graphic has eight frames, as indicated by the counter in the lower right corner. Molecules are symbolized by letter pairs or triplets and Photons by ovals and arrows. The view is of a small portion of the cloud-free Atmosphere.
- During the daytime, Solar energy enters the Atmosphere in the form of Photons at wavelengths from about 0.1μ (micron – millionth of a meter) to 4μ, which is called “shortwave” radiation and is represented as ~1/2μ and symbolized as orange ovals. Most of this energy gets a free pass through the cloud-free Atmosphere. It continues down to the Surface of the Earth where some is reflected back by light areas (not shown in the animation) and where most is absorbed and warms the Surface.
- Since Earth’s temperature is well above absolute zero, both day and night, the Surface radiates Photons in all directions with the energy distributed approximately according to a “blackbody” at a given temperature. This energy is in the form of Photons at wavelengths from about 4μ to 50μ, which is called “longwave” radiation and is represented as ~7μ, ~10μ, and ~15μ and symbolized as violet, light blue, and purple ovals, respectively. The primary “greenhouse” gases (GHG) are Water Vapor (H2O) and Carbon Dioxide (CO2). The ~7μ Photon is absorbed by an H2O molecule because Water Vapor has an absorption peak in that region, the ~10μ Photon gets a free pass because neither H2O nor CO2 absorb strongly in that region, and one of the 15μ Photons gets absorbed by an H2O molecule while the other gets absorbed by a CO2 molecule because these gases have absorption peaks in that region.
- The absorbed Photons raise the energy level of their respective molecules (symbolized by red outlines).
- The energized molecules re-emit the Photons in random directions, some upwards, some downwards, and some sideways. Some of the re-emitted Photons make their way out to Space and their energy is lost there, others back down to the Surface where their energy is absorbed, further heating the Earth, and others travel through the Atmosphere for a random distance until they encounter another GHG molecule.
- This frame and the next two illustrate another way Photons are emitted, namely due to collisions between energized GHG molecules and other air molecules. As in frame (2) the Surface radiates Photons in all directions and various wavelengths.
- The Photons cause the GHG molecules to become energized and they speed up and collide with other gas molecules, energizing them. NOTE: In a gas, the molecules are in constant motion, moving in random directions at different speeds, colliding and bouncing off one another, etc. Indeed the “temperature” of a gas is something like the average speed of the molecules. In this animation, the gas molecules are fixed in position because it would be too confusing if they were all shown moving and because the speed of the Photons is so much greater than the speed of the molecules that they hardly move in the time indicated.
- The energized air molecules emit radiation at various wavelengths and in random directions, some upwards, some downwards, and some sideways. Some of the re-emitted Photons make their way out to Space and their energy is lost there, others back down to the Surface where their energy is absorbed, further heating the Earth, and others travel through the Atmosphere for a random distance until they encounter another GHG molecule.
- Having emitted the energy, the molecules cool down.
5 - Light and Heat
Solar “light” radiation in = Earth “heat” radiation to Space out! That’s old news to those of us who understand all energy is fungible (may be converted to different forms of energy) and energy/mass is conserved (cannot be created nor destroyed).
My Visualizing series [Physical Analogy, Atmospheric Windows, Emission Spectra, and Molecules/Photons] has garnered almost 2000 comments, mostly positive. I’ve learned a lot from WUWT readers who know more than I do. However, some commenters seem to have been taken in by scientific-sounding objections to the basic science behind the Atmospheric “Greenhouse Effect”. Their objections seemed to add more heat than light to the discussion. This posting is designed to get back to basics and perhaps transform our heated arguments into more enlightened understanding :^)
Read more detail at WUWT, including the 958 responses (comments received and my brilliant replies!)...
ANSWERING THREE OBJECTIONS TO BASIC ATMOSPHERIC “GREENHOUSE EFFECT” SCIENCE
First of all, let me be clear where I am coming from. I’m a Lukewarmer-Skeptic who accepts that H2O, CO2 and other so-called “greenhouse gases” in the Atmosphere do cause the mean temperature of the Earth Surface and Atmosphere to be higher than they would be if everything was the same (Solar radiation, Earth System Albedo, …) but the Atmosphere was pure nitrogen.
The main scientific question for me, is how much does the increase in human-caused CO2 and human-caused albedo reduction increase the mean temperature above what it would be with natural cycles and processes? My answer is “not much”, because perhaps 0.1ºC to 0.2ºC of the supposed 0.8ºC increase since 1880 is due to human activities. The rest is due to natural cycles and processes over which we humans have no control. The main public policy question for me, is how much should we (society) do about it? Again, my answer is “not much”, because the effect is small and a limited increase in temperatures and CO2 may turn out to have a net benefit.
So, my motivation for this Visualizing series is not to add to the Alarmist “the sky is falling” panic, but rather to help my fellow Skeptics avoid the natural temptation to fall into an “equal and opposite” falsehood, which some of those on my side, who I call “Disbelievers”, do when they fail to acknowledge the basic facts of the role of H2O and CO2 and other gases in helping to keep temperatures in a livable range.
Objection #1: Visual and near-visual radiation is merely “light” which lacks the “quality” or “oomph” to impart warmth to objects upon which it happens to fall.
Answer #1: A NASA webpage targeted at children is sometimes cited because they say the near-IR beam from a TV remote control is not warm to the touch. Of course, that is not because it is near-visual radiation, but rather because it is very low power. All energy is fungible, and can be changed from one form to another. Thus, the 240 Watts/m^2 of visible and near-visible Solar energy that reaches and is absorbed by the Earth System, has the effect of warming the Earth System exactly as much as an equal number of Watts/m^2 of “thermal” mid- and far-IR radiation.
Objection #2: The Atmosphere, which is cooler than the Earth Surface, cannot warm the Earth Surface.
Answer #2: The Second law of Thermodynamics is often cited as the source of this falsehood. The correct interpretation is that the Second Law refers to net warming, which can only pass from the warmer to the cooler object. The back-radiation from the Atmosphere to the Earth Surface has been measured (see lower panel in the above illustration). All matter above absolute zero emits radiation and, once emitted, that radiation does not know if it is travelling from a warmer to a cooler surface or vice-versa. Once it arrives it will either be reflected or absorbed, according to its wavelength and the characteristics of the material it happens to impact.
Objection #3: The Atmospheric “Greenhouse Effect” is fictional. A glass greenhouse works mainly by preventing or reducing convection and the Atmosphere does not work that way at all.
Answer #3: I always try to put “scare quotes” around the word “greenhouse” unless referring to the glass variety because the term is misleading. Yes, a glass greenhouse works by restricting convection, and the fact that glass passes shortwave radiation and not longwave makes only a minor contribution.
Thus, I agree it is unfortunate that the established term for the Atmospheric warming effect is a bit of a misnomer. However, we are stuck with it. But, enough of semantics. Notice that the Earth System mean temperature I had to use to provide 240 Watts/m^2 of radiation to Space to balance the input absorbed from by the Earth System from the Sun was 255 K. However, the actual mean temperature at the Surface is closer to 288 K. How to explain the extra 33 K (33ºC or 58ºF)? The only rational explanation is the back-radiation from the Atmosphere to the Surface.