The GHE is calculated by working out the effective/expected temperature of 'the surface' of a planet by just looking at how much radiation it absorb (i.e. incoming solar radiation minus the amount reflected) and plugging the number (240 W/m2 average for Earth) into the clever formula.
The 'surface' means 'whatever the sunshine hits first', which on Earth is mainly clouds; or all clouds in the case of Venus. So you are actually calculating the expected temperature of the clouds; the Alarmist trick is to compare/confuse that 'surface' (from the point of view of incoming radiation) with what we mere mortals consider to the the surface i.e. land and oceans, which are of course a lot warmer because of the gravito-thermal effect (unless you go to the top of Mount Everest, which is above the clouds and hence no GHE there either).
The clever formula works much better when applied to Mars or the Moon, which have little or no clouds. The actual surface temperatures are pretty close to the calculated effective temperatures (if you adjust for solar angle and night-time cooling; but there's also little or no atmosphere so you don't need to worry about warmth being transferred from Equator to Poles or from day side to night side).
Luckily, on Earth there are also places with little or no clouds; they are called deserts. The Sahara straddles the Tropic of Cancer, so it gets peak 1,361 W/m2 sunshine at midday during the summer months. Divide that by the sq root of two to get average during a 12-hour day = 962 W/m2; halve that for the 12-hour night = 481 W/m2; then knock off one-fifth reflected = 385 W/m2.
Plug 385 W/m2 into the formula and you get an expected average temperature of 287K. Deserts have a large diurnal temperature range, just like The Moon (they cool down fast during the night because there is no cloud blanket), of (say) 40 degrees. A typical desert near the equator is just above freezing just before dawn and 40 degrees hotter in the early afternoon, so the average actual temperature is about 293K.
OK, that's six degrees warmer than expected and these are only back of an envelope calculations, but it's nowhere near the much vaunted 33 degree Greenhouse Effect, despite there being more CO2 than average above the Tropics (the troposphere is thickest over The Equator and thinnest over The Poles).
[We could also dispense with the whole concept of averaging sunshine over 24 hours and look at the hypothetical peak radiation of about 1,000 W/m2 at midday in summer, plug that into the formula and we get peak temp of 364K = 91C. Temperatures get nowhere near that, but to the extent they do, that might explain the 6 degree discrepancy?]
The answer to the question in the title is of course "Because there are no bloody clouds over the desert, and the Greenhouse Effect on Venus or Earth is purely down to clouds and their altitude!", just in case you were wondering.
Sunday, 17 October 2021
Why is there no Greenhouse Effect in the desert?
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37 comments:
Thinking about deserts is a great idea. Did you pick the equator to make the maths possible? There are no deserts at the equator which is tropical. Perhaps this is the source of your back of an envelope 6 degrees. The average high in the Sahara in summer is 40, but that is when the northern hemisphere is tilted at the sun and the days are longer.
OTOH, you are quite right re where deserts are, I was simplifying.
Clearly, the Sahara straddles the tropic of Cancer, so my back of envelope applies there during the summer months.
I could get rid of the 6 degrees by tinkering with the wild guess "20% reflected", but I'm not going for absolute precision, the point is it sure as heck isn't 33 degrees out.
Your theory is wrong. You propose that the land and oceans are heated by the atmosphere. The land and oceans thermal capacity is 1000 times greater than the atmosphere and the average temperature of the land and oceans is higher than the average temperature of the atmosphere. And so it is impossible.
Din, I propose no such thing; please understand it first, Lord knows I have tried explaining it to you bit by bit in easily understandable chunks.
For example, which of these do you actually dispute?
1. The land and ocean surface will tend to be at the same temperature at the air resting on it.
2. Thermal energy is just one form of energy. Other forms of energy relevant in a climate and weather context) are potential energy and the latent heat of evaporation.
3. All these types of energy are measured in the same units and energy can change from one type to another and back again.
You propose that the land and oceans are heated by the atmosphere. The land and oceans thermal capacity is 1000 times greater than the atmosphere and the average temperature of the land and oceans is higher than the average temperature of the atmosphere. And so it is impossible. Your theory creates energy out of nowhere.
OTOH, thanks for reminder re where deserts are, I have updated that section to make it clearer.
Din, I will answer your question on the assumption that you will reply to mine above:
"You propose that the land and oceans are heated by the atmosphere."
I merely observe and accept that the land and ocean surfaces are the same temp as the air immediately above them, give or take a bit. Do you dispute that????
Din, in fact, we could flip your nonsense round to the equally nonsensical statement/question:
"It is only the top few inches of land or water that are in thermal equilibrium with the air above it. Per square metre of surface, how can a few hundred kg of rocks or water warm up a 10 km high column of air with a mass of 10 tonnes?"
For the land and oceans to be at the temperature that they are at requires a certain amount of heat energy in accordance with their heat capacity. The heat input in your theory is a lower amount of heat energy . The heat input in your theory is that which is absorbed by clouds and those clouds have a considerably lower heat capacity ( approx 1000 times ) and so your theory is impossible.
Din, like all Alarmists, you refuse to answer direct questions.
So here's another one which you won't answer- what's more plausible
a) ten tonnes of air warms a few hundred kg of rocks or water, or
b) a few hundred kg of rocks or water warm ten tonnes of air?
I am not an alarmist you must have mistaken me for someone else.
You are missing the point that I clearly made in the last comment.
In your theory there is not enough heat input.
For the land and oceans to be at the temperature that they are at requires a certain amount of heat energy in accordance with their heat capacity. The heat input in your theory is a lower amount of heat energy . The heat input in your theory is that which is absorbed by clouds and those clouds have a considerably lower heat capacity ( approx 1000 times ) and the land and oceans average temperature is higher than the clouds , and so your theory is impossible.
Din, if you refuse to reply to a single one of my simple questions then there is not point to this.
Answer them all to the best of your knowledge and belief and then I'll have a think.
You simply repeating the same old gibberish over and over is no way to have a serious discussion.
A serious discussion discusses scientific principles . But your questions are not part of a scientific discussion, they are random questions with no underlying narrative. That is why I stick to the scientific principles. For example of the randomness, at 10.33 you say that your theory does not include the atmosphere heating the land and oceans and then at 19.05 you ask me to comment on your then explicitly self contradictory pontification that the atmosphere heats the land and oceans. That is why I stick to scientific fact.
Nothing in my comment is Gibberish , it is an irrefutable description of the system being studied and that is why you have not refuted it.
For the land and oceans to be at the temperature that they are at requires a certain amount of heat energy in accordance with their heat capacity. The heat input in your theory is a lower amount of heat energy . The heat input in your theory is that which is absorbed by clouds and those clouds have a considerably lower heat capacity ( approx 1000 times ) and the land and oceans average temperature is higher than the clouds , and so your theory is impossible.
Given enough time, does relative 'heat capacity' matter? My heavy iron skillet can gain or lose energy and temperature from the air around it. If I put the central heating on, the skillet can gain energy from the air. Or, imagine that my house was sealed and I compressed the air, raising it's temperature. The air would still slowly transfer that energy to the skillet.
Din, you don't realise that you don't understand it.
That's why you think my questions are random. They are not. I want you to answer them so that I can work out which step in the logic you don't understand.
For the benefit of anybody yet to make up their minds, let's look at Din's statement:
"For the land and oceans to be at the temperature that they are at requires a certain amount of energy in accordance with their heat capacity."
1. One sq metre of Earth's surface (or one sq metre of clouds) get average about 20 million Joules of energy from the Sun per day.
2. One sq metre of Earth and the vertical column or air and cloud above it has a total specific heat capacity of about 10 million Joules.
3. The energy from the Sun comes in and warms up that one square metre plus all the air above it, by theoretically 2 degrees per day.
4. The one square metre and the air and clouds above it stop warming up when they are so warm that they emit as much radiation back to space as they are getting from the Sun.
5. Most people envisage the sunshine hitting the ground and keeping the air warm. In truth, more sunshine hits the clouds than hits the ground.
6. But it's the same total energy coming in and the same mass of air + land + water that's being kept at the same basic temperature.
7. It doesn't make a HUGE MASSIVE difference whether Sun hits ground or hits clouds. It's the same 20 million Joules coming in and going out every day.
8. It does of course make a MEDIUM SIZED difference if Sun hits clouds because that dictates their temperature; the clouds warm the air up there to the same temp; the air up there also has Potential Energy (altitude x mass); the air down below has to have more thermal energy to make up for the fact it has no Potential Energy - energy is in balance as you go up in the troposphere, if you add the main types together for each layer (thermal, potential and latent heat of evaporation).
OTOH, thanks, good exa,ple.
Din, you have also completely missed the basic point of the post that there is little or no GHE in the desert.
We don't need to argue about clouds because there are fewer clouds over the desert, so let's ignore them.
Din, same goes for top of Everest - hardly any clouds above it, it's above most clouds and also no GHE (possible slightly negative GHE).
OTOH,
The total heat capacity of your iron skillet is tiny compared to the total heat capacity of all the atmosphere in your house. That is why it varies with room temperature. If you had a huge skillet comparable to the volume of the house and the skillet is at cool temperature , the air temp of the house would reduce.
Din, exactly!
Equally, the total heat capacity of a few hundred kg of land or water are also tiny compared to the total heat capacity of ten tonnes of air above them (going on a square metre basis).
So what's more likely,
A) land and water warms air above it or
B) air warms land and water below it?
This is all a complete sideshow anyway, but hey.
Mark,
Fundamentally the issue is not whether the heat energy (33 multiplied by the total heat capacity of the total quantity of effected material of oceans, land or atmosphere) started in the land or clouds. The issue is that it is unequivocally present in the planet earth system and a correct theory must include a mechanism to explain its presence. Your theory does not do that. The GHG theory for example, explains the presence of it with insulation. Your theory regects that concept of atmospheric insulation.
I dont have the a really good link but these are relevant in that they indicate the quantities involved.
https://scholarsandrogues.com/2013/05/09/csfe-heat-capacity-air-ocean/
https://ocean-climate.org/wp-content/uploads/2020/01/1.-The-ocean-a-heat-reservoir-scientific-fact-sheets-2019.pdf
https://www.science.org/doi/10.1126/sciadv.1601545
https://www.climate.gov/news-features/blogs/enso/role-ocean-tempering-global-warming
Din, you baldly state
"a correct theory must include a mechanism to explain [the GHE's ] presence. Your theory does not do that"
That's the point.
The observed 33 deg GHE is - quite simply - the difference between cloud temp/the effective temp and the sea level temp.
The effective temp and hence the 33 deg GHE is calculated on the basis "of what the sunshine hits first", which is clouds (if there are any).
Specific heat capacity has little to do with it.
The land, oceans, air, clouds, whatever are warmed by sunshine, by theoretically 2 deg each day.
They warm up until they are radiating as many Joules back to space as they get from the Sun. Doesn't matter what their total specific heat capacity is. Whatever it is, they will reach whatever temp is required to radiate those Joules back again.
The clouds are the main thing that absorb/receive sunshine and the main thing that radiate back to space.
This goes for Venus even more than Earth. It doesn't go for Mars or Moon because there are no clouds there, and hence no GHE.
Don't get me started on Gas Giants.
You misquoted me . I said , a correct theory must include a mechanism to explain the presence of the heat energy.
Din, the energy cones in from the sun. Have I not mentioned that several times?
The heat energy for the effective temperature is explained as the initial incoming flux from the sun . But what about the heat energy to maintain the temperature of the oceans land and atmosphere where they are above the effective temperature. Temperature is caused by the presence of heat energy. That is 33 multiplied by the total heat capacity of the total quantity of effected material of oceans, land and atmosphere. The GHG theory explains the presence of that thermal energy with downwards IR . In your theory there is only the initial incoming solar flux. In you theory there is no more energy than that which appears in the effective temperature equation. And so your theory misses the point that the GHG theory addresses.
Din, I'm not sure what you are arguing about. Surely it's very simple: is there a greenhouse effect in the desert or not? The answer to this question doesn't depend on what causes the greenhouse effect, so why bring it up?
Din, "That is 33 multiplied by the total heat capacity of the total quantity of effected material of oceans, land and atmosphere"
Agreed.
As I have explained - which is obvious to anybody interested in these matters - 20 million W/m2 comes in every day from the Sun.
Although total spec. heat capacity is ginormous, the whole system steadily warms up until it reaches the temperature at which it is warm enough to emit as much IR as it receives in sunshine.
"The GHG theory explains the presence of that thermal energy with downwards IR"
No it doesn't. They made up a number that says the GHG's somehow double solar radiation. So that is 40 million W/m2 per day. Still a tiny number compared to total heat capacity.
Using your insane logic, if 20 million watts can't do it, then neither can 40 million.
In real life, to use Hansen's leaky bucket analogy, no matter how big the bucket (= total heat capacity), whether water (= radiation) is dripping in slowly or quickly, sooner or later it will fill up and start overflowing (= reach the temperature at which it is radiating as much energy to space as incoming sunshine).
Din, you really haven't understood it, have you:
"In your theory there is no more energy than that which appears in the effective temperature equation"
In real life, there is POTENTIAL ENERGY as well as thermal energy. If you think there's energy missing from my explanation of real life it is because you have fallen into the Alarmist trap of ignoring potential energy.
To repeat for anybody reading this who's actually interested and not a time-waster.
Clouds and the air surrounding them have a certain temperature (dictated by incoming sunshine) and are also high up, so they also have potential energy (gravity x altitude x mass) = total energy X.
Air at sea level has the same total energy X but as it cannot have potential energy (it can't go any lower), it has more thermal energy to balance it out = it is warmer than expected if you just look at sunshine being absorbed by clouds.
"...the whole system steadily warms up until it reaches the temperature at which it is warm enough to emit as much IR as it receives in sunshine."
It does not do that . Some of it is up to 33 Degrees higher than from what it receives from the initial incoming flux of sunshine.
That is the whole point of the issue that the GHG theory addresses.
And you are missing the whole point of what the GHG theory addresses.
Din, you are clearly either certifiably insane or you have the attention span of a goldfish with amnesia.
Mark, it seems that, like the Scots at Flodden, you have been lured to fight your opponents on their chosen ground. All this crap about solar flux and atmospheric temperatures is irrelevant to the crucial question, is there a greenhouse effect in the desert or isn't there?
If there isn't, the whole GHG theory falls to the ground, making completely irrelevant what may or may not be causing it. If there is a greenhouse effect in one place and not in another place where the air has the same composition, what is causing the greenhouse effect cannot be the composition of the air. There is no need for any complicated explanations involving the gravito-barometric theory, or the scattering effect of CO2. It really is the Killer Argument.
B, excellent summary. There's also no GHE at the top of Everest.
The problem with this Killer Argument is that most people have very little idea what the Greenhouse Effect actually is and think it's the same as Global Warming.
B, yes, the powers that be present it as a given that the 33 degrees difference is down to CO2, therefore any increase in CO2 = higher temps. And most people swallow it.
The CO2 has bugger all to do with the 33 degrees, so the conclusion does not follow.
I offer no opinion on why temperatures vary slightly over time, I guess this is the same as the Roman and Mediaeval Warm Periods, they come along even 1,000 years or so.
Mark I do not have the attention span of a Goldfish. That is you - if I do not repeat a summary of every previous point in every comment, then you take the last comment only and reply to that comment only, out of context of the rest. ie your comments do not follow the thread.
So Here is a Summary
The earth system , atmosphere land oceans, contains more heat energy than that which appears in the effective temperature equation.
The purpose of the Greenhouse theory is to explain why the KNOWN TOTAL ENERGY IS GREATER. Your theory does not even try to explain this and so you theory is not an alternative to the GHG theory.
Your theory has a Kinetic and Potential energy gradient, of the SAME TOTAL ENERGY as the effective temperature equation and so your theory is not an alternative to the GHG theory explanation.
Din, you keep making the same mistakes.
"The purpose of the Greenhouse theory is to explain why the KNOWN TOTAL ENERGY IS GREATER. Your theory does not even try to explain this and so you theory is not an alternative to the GHG theory."
There is a Greenhouse Effect, measured as difference between effective temp/actual temp of clouds (which absorb most of the sunshine) and the actual temp at sea level. That is how we work out the 33 degree GHE!
There is a temperature gradient (dictated by effective temp and lapse rate) and there is a potential energy gradient (dictated by altitude).
The known total energy is exactly what you'd expect.
You multiply temperature x mass x specific heat capacity = thermal energy. Remember - you work out temp first and then multiply up to get energy!!
You multiply mass x altitude x acceleration due to gravity = potential energy.
Add them together, plus a bit more for latent heat and Bob's your uncle.
Here's a handy infographic.
There is no great mystery about any of this, it's GCSE level physics, absolutely unarguable and basic.
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