What If There Was No Greenhouse Effect?
by Roy W. Spencer, Ph. D.
The climate of the Earth is profoundly affected by two competing processes: the greenhouse effect, which acts to warm the lower atmosphere and cool the upper atmosphere, and atmospheric convection (thermals, clouds, precipitation) which does just the opposite: cools the lower atmosphere and warms the upper atmosphere.
To better understand why this happens, it is an instructive thought experiment to ask the question: What if there was no greenhouse effect? In other words, what if there were no infrared absorbers such as water vapor and carbon dioxide in the atmosphere?
While we usually only discuss the greenhouse effect in the context of global warming (that is, the theory that adding more carbon dioxide to the atmosphere will lead to higher temperatures in the lower atmosphere), it turns out that the greenhouse effect has a more fundamental role: there would be no weather on Earth without the greenhouse effect.
First, the big picture: The Earth surface is warmed by sunlight, and the surface and atmosphere together cool by infrared radiation back to outer space. And just as a pot of water warming on the stove will stop warming when the rate of energy gained by the pot from the stove equals the rate of energy loss by the pot to its surroundings, an initially cold Earth would stop warming when the rate at which solar energy is absorbed equals the rate at which infrared energy is lost by the whole Earth-atmosphere system to space.
So, let’s imagine an extremely cold Earth and atmosphere, without any water vapor, carbon dioxide, methane or any other greenhouse gases – and with no surface water to evaporate and create atmospheric water vapor, either. Next, imagine the sun starts to warm the surface of the Earth. As the surface temperature rises, it begins to give off more infrared energy to outer space in response.
That’s the Earth’s surface. But what would happen to the atmosphere at the same time? The cold air in contact with the warming ground would also begin to warm by thermal conduction. Convective air currents would transport this heat upward, gradually warming the atmosphere from the bottom up. Importantly, this ‘dry convection’ will result in a vertical temperature profile that falls off by 9.8 deg. C for every kilometer rise in altitude, which is the so-called ‘adiabatic lapse rate’. This is because rising warm air parcels cool as they expand at the lower air pressures aloft, and the air that sinks in response to all of that rising air must warm at the same rate by compression.
Eventually, the surface and lower atmosphere would warm until the rate at which infrared energy is lost by the Earth’s surface to space would equal the rate at which sunlight is absorbed by the surface, and the whole system would settle into a fairly repeatable day-night cycle of the surface heating (and lower atmosphere convecting) during the day, and the surface cooling (and a shallow layer of air in contact with it) during the night.
The global-average temperature at which this occurs would depend a lot on how reflective the Earth’s surface is to sunlight in our thought experiment. ..it could be anywhere from well below 0 deg F for a partially reflective Earth to about 45 deg. F for a totally black Earth.
So, how is this different from what happens in the real world? Well, notice that what we are left with in this thought experiment is an atmosphere that is heated from below by the ground absorbing sunlight, but the atmosphere has no way of cooling…except in a very shallow layer right next to the ground where it can cool by conduction at night.
Why is this lack of an atmospheric cooling mechanism important? Because in our thought experiment we now have an atmosphere whose upper layers are colder than the surface and lower atmosphere. And what happens when there is a temperature difference in a material? Heat flows by thermal conduction, which would then gradually warm the upper atmosphere to reduce that temperature difference. The process would be slow, because the thermal conductivity of air is quite low. But eventually, the entire atmosphere would reach a constant temperature with height.
Only the surface and a shallow layer of air next to the surface would go through a day-night cycle of heating and cooling. The rest of the atmosphere would be at approximately the same temperature as the average surface temperature. And without a falloff of temperature with height in the atmosphere of at least 10 deg. C per kilometer, all atmospheric convection would stop.
Since it is the convective overturning of the atmosphere that causes most of what we recognize as ‘weather’, most weather activity on Earth would stop, too. Atmospheric convective overturning is what causes clouds and rainfall. In the tropics, it occurs in relatively small and strongly overturning thunderstorm-type weather systems.
At higher latitudes, that convection occurs in much larger but more weakly overturning cloud and precipitation systems associated with low pressure areas.
There would probably still be some horizontal wind flows associated with the fact that the poles would still be cooler than the tropics, and the day-night heating cycle that moves around the Earth each day. But for the most part, most of what we call ‘weather’ would not occur. The same is true even if there was surface water and water vapor…but if we were able to somehow ‘turn off’ the greenhouse effect of water vapor. Eventually, the atmosphere would still become ‘isothermal’, with a roughly constant temperature with height.
Why would this occur? Infrared absorbers like water vapor and carbon dioxide provide an additional heating mechanism for the atmosphere. But at least as important is the fact that, since infrared absorbers are also infrared emitters, the presence of greenhouse gases allow the atmosphere — not just the surface — to cool to outer space.
When you pile all of the layers of greenhouse gases in the atmosphere on top of one another, they form a sort of radiative blanket, heating the lower layers and cooling the upper layers. (For those of you who have heard claims that the greenhouse effect is physically impossible, see my article here. There is a common misconception that the rate at which a layer absorbs IR energy must equal the rate at which it loses IR energy, which in general is not true.)
Without the convective air currents to transport excess heat from the lower atmosphere to the upper atmosphere, the greenhouse effect by itself would make the surface of the Earth unbearably hot, and the upper atmosphere (at altitudes where where jets fly) very much colder than it really is.
Thus, it is the greenhouse effect that continuously de-stabilizes the atmosphere, ‘trying’ to create a temperature profile that the atmosphere cannot sustain, which then causes all different kinds of weather as the atmosphere convectively overturns. Thus, the greenhouse effect is actually required to explain why weather occurs.
This is what makes water such an amazing substance. It cools the Earth’s surface when it evaporates, it warms the upper atmosphere when it re-condenses to form precipitation, it warms the lower atmosphere through the greenhouse effect, and it cools the upper atmosphere by emitting infrared radiation to outer space (also part of the greenhouse effect process). These heating and cooling processes are continuously interacting, with each limiting the influence of the other.
As Dick Lindzen alluded to back in 1990, while everyone seems to understand that the greenhouse effect warms the Earth’s surface, few people are aware of the fact that weather processes greatly limit that warming. And one very real possibility is that the 1 deg. C direct warming effect of doubling our atmospheric CO2 concentration by late in this century will be mitigated by the cooling effects of weather to a value closer to 0.5 deg. C or so (about 1 deg. F.) This is much less than is being predicted by the UN’s Intergovernmental Panel on Climate Change or by NASA’s James Hansen, who believe that weather changes will amplify, rather than reduce, that warming.
“astonerii (17:51:38) :
[…]
if there was a feedback mechanism for greenhouse effects, it would have already taken the earth to boiled ocean temperatures.”
See my comment above. Think about an echo effect in music: When you have an echo with half the amplitude of the original and add it to the input, you get a limes of 2*input even though the echoing proceeds endlessly. This is not even dampened by a logarithmic function. With GHG’s we have logarithmic dampening of the feedback due to the saturation effects so it very quickly ebbs.
IMHO the IPCC has intentionally overestimated this vastly to make sure there’s a scare story. But a (water vapour) feedback is in principle logical.
Paul (17:42:38)
“Just ask the Martians where the winds surely do blow.”
I knew it!
…and stop calling me surely.
Just some of teh properties. Other properties, that are in fact (or also) essential to life are:
1. The extremely rare property (one of 5 substances, I think?) of the solid being less dense than the liquid. This allows ice to float, thus protecting water creatures (as all were at one time) from dying when air temps get too low, as well as breaking rocks into smaller rocks, and then soil, by getting into cracks and freezing.
2. Its very good abilities as a solvent. As I recall, life as we know it could not exist without this property. I recall alcohol is also a very good solvent, but its toxicity to most known life prevent it from being useful (apart from for entertainment of some higher life forms).
3. high surface tension
4. Heat capacity (evident here)
lots more I cannot recall….
Think more dearly of that humble glass of water next time you drink one, without it, we’d not be here!
Paul (17:42:38):
“you might not want to use this site as your only education if this post is representative of the state of its science.”
Aside from the fact that Dr Spencer has forgotten more climate science than you will ever learn, you should be aware that this “Best Science” site encourages all points of view, including yours.
Compare that with the typical climate alarmist sites, which actively censor points of view that do not buy into their AGW scare.
Any sites that have to censor opinions that are contrary to the Party line do not have truth on their side. So stick around here, if you think you have credible arguments. You can comment and discuss the issues; eventually the bogus arguments fall by the wayside, and what we’re left with is more or less the truth.
Go ahead, give it a try. If you think Dr Spencer is misleading you, make your case. You could start by defining “weather”, so we’re all on the same page; weather isn’t just wind. When we talk about ‘weather’, there are usually clouds involved. Maybe you could tell us how to make clouds without H2O.
“But eventually, the entire atmosphere would reach a constant temperature with height.”
No way Watts. The planet still rotates, so there would still be wind. And with wind blowing across oceans (we have to assume zero evaporation for your hypothetical, but some liquid has to be part of the model) and mountain ranges you get wind patterns that will be random.
The gas giants have no CO2 or H2O, mostly Nitrogen, and they have some ean storms with changing patterns.
Air pressure, cloud cover and a variety of non ghg related factors seem to be the main heat retaining factors, and its forgotten that even if there were no ghg;s, heat would sit in the atmosphere for quite some time.
I tell a lie. the Coriolis force has been proved to affect draining sinks – but only when left for a week!
http://www.ems.psu.edu/~fraser/Bad/BadCoriolis.html
Paul (17:42:38) :
Wow. No greenhouse = no weather? Just ask the Martians where the winds surely do blow. Strange that a scientist from NASA would so mislead. All you skeptics out there: you might not want to use this site as your only education if this post is representative of the state of its science.”
If you actually read the article instead of being in such a tearing hurry to post your cheap shot you would know that there is a valid reason for Martian winds without a greenhouse effect, the author was explicit.
“What if there was no greenhouse effect? In other words, what if there were no infrared absorbers such as water vapor and carbon dioxide in the atmosphere?”
=====================================
Marie Curie quote:
“I am among those who think that science has great beauty. A scientist in his laboratory is not only a technician: he is also a child placed before natural phenomena which impress him like a fairy tale.”
she probably didn’t believe in fairy tales, or “what if’s”
Paul (17:42:38) :
Interesting. I, for one, find WUWT to provide a great deal of valid science and science discussion. Perhaps that is only because I actually knew something before I started visiting the site.
Others have pointed out your error in referring to Mars as an example of your extensive knowledge. Hence, I shall not repeat that revelation. I will ask though; do you know of a planet, which has an atmosphere, that does not contain any greenhouse gases?
You cannot have a watery planet without “greenhouse gasses”; those oceans evaporate and form clouds, etc.
Dr. Spencer is having some fun with a “spherical planet”
Lindzen and Choi publish in 2009 that asignificant proportion of radiation isn’t affected by ghg’s and that radiation is emitted and re-emitted over and over – in other words, that ghg’s don’t trap heat that leads to a heat accumulation. Radiative atmospherics studies as though its emitting from a black body with a two dimensional surface, almost forgeting that most radiation goes straight through ghg’s, specifically c02 – the difference between gases and two dimensional surfaces is that gases have more dimensions so lose/emit heat much more effectively: So the speculation is that if there were no ghg’s, the surface temperature would be the same, but weather patterns would be different, and the upper troposphere would be slightly cooler.
pft,
You are correct that the upper layer radiation out (including from gases at the upper level plus direct radiation from the ground) would equal the absorbed input at equilibrium. The only time it is lower is while the ground temperature (or energy storage in the oceans) is increasing. Since it stopped increasing the last few years, and ocean storage seems low to slightly negative, the upper layer radiation has to approximately match the input. The only way that can be reduced is for the input level (Solar energy) to be lower also.
The comments on black body radiation for gases is not valid. The fairly narrow spectral lines due to molecular energy states such as vibration are the only way molecular gases absorb or emit at the low temperatures encountered in the atmosphere. Oxygen and Nitrogen have a few weak lines of interest, so would cause some greenhouse effect. However, the gases would not absorb a significant amount of the ground radiation, so direct radiation to space would cool the ground to a lower temperature.The net lapse rate with just these gases would depend on the result of the combination of diffusion and convection under the lower re-radiation effects.
Paul (18:01:41) :
Ok Paul. You say “Mars does have a mostly CO2 atmosphere, but because of the very low surface pressure, it has little radiative influence Mars does have a mostly CO2 atmosphere, but because of the very low surface pressure, it has little radiative influence…”.
Since Mars atmospheric pressure is ~1/100 of Earth and since Earth only has 380PPM of CO2 compared to 90% on Mars, this make Earth CO2 partial pressure tiny compared to on Mars.
I guess you are saying CO2 has basically no radiative influence at all on Earth. It that right?
Roy W. Spencer, Ph. D.
I think this post was a bad idea for your ‘street cred’ Roy.
The scenarios you suggest are impossible, even in a ‘thought experiment’. For example:
There is no way that a planet with so much water would ever generate an atmosphere without water vapour (WV), as even ice sublimates. Though, if there were no ‘radiative gasses’ in the atmosphere, the atmosphere would neither radiate, or absorb, radiation more than its natural LTE (local thermodynamic equilibrium) temperature equivalent (again, a most unlikely scenario, given the expected gasses from any ‘planetary surface warming’ of a rotating planet [I exclude satellites, or ‘moons’, as they tend to undergo gravitational loss of atmosphere to their ‘parent’ body]).
Your statement “there would be no weather on Earth without the greenhouse effect.” seems so wrong. Without the temperature ‘hot spot normalisation’ ameliorated by radiative influence, the ‘normalisation’ of temperature ‘hot spots’ is left solely to the ‘thermals’ that cause ‘weather’. So! In a ‘radiative gas-less Earth’, only ‘surface albedo’ rules with its associated level of increased thermal convection! I can’t reconcile this within your scenario Roy. Especially when LTE is disturbed by lack of radiative influence, (this is almost unheard of) as it’s always there where an atmosphere exists.
This is half of what I want to say, but it’s both late for me and should be enough for an initial query.
Best regards, suricat.
All:
What we all generally consider “weather” is driven by thermodynamical instabilities. These are generally driven by differential heating or cooling. Some of this (e.g. upper atmosphere cooling) is certainly directly related to greenhouse gases (and radiation to space from non-gases such as cloud), but many other processes (e.g. heating at the equator cooling at the poles) also produce instabilities. Mars certainly has weather and has a very feeble greenhouse.
http://www.ozgate.com/infobytes/mars_weather.htm
Well, what do you know, my grade school science book was right, we do live in a mostly closed loop world. It’s amazing how many lay people believe in AGW, but have no idea that the earth can and does actually have mechanisms to cool as well as warm this place we call home.
Needless to say most of the higher theories that get discussed here just goes right over my head (not a climate scientist), but I’ve noticed that generally when people have AGW discussions, I rarely see much common sense applied to anything. (The reasoning that we are running out of water just dumbfounds me…).
I would assume that the good old-fashioned, well tested physics rules would still apply. I do realize that external inputs will cause all sorts of chaotic I/O, but still…
RE: Alex Harvey (16:39:03) :
Alex, all matter emits blackbody radiation, although you are right that gases are not blackbodies.
Some poster here seem to confuse a substances Infared emmision spectrum with its absorption spectrum, they are two separate and different things.
Oxygen is not at all a weak greenhouse gas as it does not absorb infared radiation, as the bonds in the oxygen atom are of too high an energy to be excited by the low energy of infared.
Infared radiation is only strong enough to cause bending of triatomic and larger molecules, which is why carbon dioxide, water and methane are important. No diatomic molecules are considered greenhouse gases for this reason.
“suricat (18:53:50) :
[…]
The scenarios you suggest are impossible, even in a ‘thought experiment’. ”
Hmmm… that’s a wild statement.
“There is no way that a planet with so much water would ever generate an atmosphere without water vapour (WV), as even ice sublimates.”
In reality, you would be right. But we are in a thought experiment.
” Though, if there were no ‘radiative gasses’ in the atmosphere, the atmosphere would neither radiate, or absorb, radiation more than its natural LTE (local thermodynamic equilibrium) temperature equivalent (again, a most unlikely scenario,”
In reality, it would not be unlikely, it would be right out. But we are in a thought experiment.
” given the expected gasses from any ‘planetary surface warming’ of a rotating planet [I exclude satellites, or ‘moons’, as they tend to undergo gravitational loss of atmosphere to their ‘parent’ body]).”
Well, let’s just say as much radiation goes out as goes in.
“Your statement “there would be no weather on Earth without the greenhouse effect.” seems so wrong.”
Yes.
” Without the temperature ‘hot spot normalisation’ ameliorated by radiative influence, the ‘normalisation’ of temperature ‘hot spots’ is left solely to the ‘thermals’ that cause ‘weather’. So! In a ‘radiative gas-less Earth’, only ’surface albedo’ rules with its associated level of increased thermal convection! I can’t reconcile this within your scenario Roy. Especially when LTE is disturbed by lack of radiative influence, (this is almost unheard of) as it’s always there where an atmosphere exists.”
Surface albedo affects upward reflexion. The thought experiment says that there are no greenhouse gasses, that means no gasses that stop part of the radiated spectrum of frequencies from leaving the planet. Thus, the reflected or emitted radiation from the surface cannot warm up parts of the atmosphere, thus there would be no radiation-caused temperature differences, so no convection.
My take.
No weather without so-called greenhouse gases? Jupiter is mostly hydrogen and helium and yet the Great Red Spot has persisted for centuries.
And how is it possible that the internal temperature of Jupiter with no CO2 is greater than the surface of Venus? I’ve asked this question to a couple of professors at my local university and never gotten a reply.
Sounds a bit like Snowball Earth, which required millions of years of CO2 spewing vulcanism to thaw.
DirkH (18:01:56) :
I think you and I see eye to eye on this. I just think that the Earth has already reached its limit on greenhouse forcing for the amount of energy that is put into the system from both the solar and the internal molten core energy that is available.
wayne (18:51:41) :
Good question about the CO2 and the answer is not so straight forward. Although there are about the same number of molecules of CO2 above any sq meter on Mars as on Earth, they are not nearly as effective as a greenhouse gas because the total atmospheric pressure is much lower. The higher density of gas in Earth’s atmosphere works to spread the absorption of IR by CO2 over more of the wavelength scale. Consider building a fence out of 2×4’s spaced every 8″ (rough cut). 50% of the light hitting the fence from the side will make it through the fence. Alternatively, consider using 1 x 4 spaced every 4″. Same amount of wood, but no light would get through. This is how it works for CO2 (and H2O) on Mars and on Earth. The same amount of CO2 (or H2O) is more efficient on earth because of all the N2 and O2 colliders (this is called pressure broadening. There is a reasonable wiki page http://en.wikipedia.org/wiki/Spectral_line but it could use to be updated to discuss the role of broadening on climate.
@John J. Jupiter emits more energy than it receives in solar radiation. One therefore is drawn to the conclusion that there is something going on deep in the core of the planet.
Alex Harvey (16:01:44) :
You wrote: “I think you will find that for convection to be maintained in the long term you need not just heating from below but cooling from above. It is the cooling from above that is lacking in an IR transparent atmosphere.”
True enough. In a planet with a transparent atmosphere the “weather” would be driven by heat transport from the equator to the poles, as already mentioned by other posters, giving Mars as an example. Dr. Spencer mentions it as well, although he seems to minimize it.