What Is The Purpose Of A Greenhouse?

The purpose of a greenhouse, is to emulate the climate of the tropics.

ScreenHunter_4706 Nov. 17 10.06

The tropics are very warm, largely because of the high concentration of greenhouse gases there. During June, the Arctic receives more solar insolation than the tropics, yet is much colder. Why is that?

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62 Responses to What Is The Purpose Of A Greenhouse?

  1. Patrick Hannon, Statistician says:

    And how about this one. Saturn’s moon has approximately 1.5 bars of pressure from its atmosphere which is 95% nitrogen and 5% methane. Of course this means it has a thicker atmosphere. surface pressure is purely a factor of the amount of atmosphere and nothing to do with its temperature. It kills me to hear arguments of why the earth’s surface temperature is what it is simply due to the amount of atmosphere we have above us (and similar silly arguments for Venus). Resulting temperature is combination of factors including, but not limited to: Net energy impacting and absorbed from the sun, presence of greenhouse gases , and then finally the total amount of atmosphere. I would agree that all things being equal if we suddenly had, say, 50% more non-greenhouse gases, then the temperature at the surface would necessarily be higher.
    Anyway, I have to agree with Tony that we discredit ourselves trying to rationalize away the greenhouse effect. We will not be listened spouting off such non-sense that there’s no such thing.

    • Atmospheric pressure is the primary control of temperature, and the reason Venus is so hot. But there is no question that the greenhouse effect influences a few tens of degrees near the surface, in humid climates.

      • Bob Knows says:

        It is hot on the Sahara desert and Australia despite being dry. Try again.

      • PJ London says:

        Are you talking CO2, Methane or H2O?
        Are you suggesting that Humidity will/can vary temperature by TENS of degrees on earth?

        • A humid night can easily be tens of degrees warmer than a dry night. All of us have experienced that.

        • PJ London says:

          To Steve re humid nights.
          I can’t believe that you wrote such rubbish. If the nights were warmer (had a higher temperature, not just the appearance of being warmer) it was because of cloud cover, not humidity. Can you please provide any source to data to support your assertion.
          I have lived in hot climates where humidity has ranged from very low to very high as well as in cold climes with both humidity extremes. The only effect was that the cooling by perspiration was inhibited by high humidity and thus one’s body did not cool as efficiently. On one occasion this caused me to suffer heatstroke as the external temperature was 48c and the high humidity meant that I did not cool through sweating. The same temperature with the wind coming off the desert, allowed me to work without getting heatstroke.

        • Blah blah blah blah Humid nights with a clear sky are warmer than dry nights with a clear sky. In the Utah desert, temperatures can drop 60 degrees overnight.

        • PeterMG says:

          PJ London I agree with you. Steve/Tony needs to travel a little but unfortunately he won’t be able to go to the Arabian desert to check his theory as you need to be invited. The US is a wonderful place and I have enjoyed all my visits there but its not the whole world or even a 1/4 of it. Of all the tropical hot places I have been and lived in water has cooled not made it warmer. And Riyadh is dry as a bone 99.9% of the time except when it rains and hails which is an hilarious experience to witness in a place with no drains.

        • Saudi Arabia has the world record dew point of 95F

          Different deserts have different properties. Should I repeat that about 12 more times?

        • PJ London says:

          Blah blah blah why not go to the science?
          “Because humans perceive a low rate of heat transfer from the body to be equivalent to a higher air temperature, the body experiences greater distress of waste heat burden at high humidity than at lower humidity, given equal temperatures.

          For example, if the air temperature is 24 °C (75 °F) and the relative humidity is zero percent, then the air temperature feels like 21 °C (69 °F). If the relative humidity is 100 percent at the same air temperature, then it feels like 27 °C (80 °F). In other words, if the air is 24 °C (75 °F) and contains saturated water vapor, then the human body cools itself at the same rate as it would if it were 27 °C (80 °F) and dry. The heat index and the humidex are indices that reflect the combined effect of temperature and humidity on the cooling effect of the atmosphere on the human body.”

          Any source that shows humidity affecting temperature, other than through the cooling (by evaporation) of surfaces.

      • Patrick Hannon, Statistician says:

        Hmmm … I’ll bite 🙂 … then why would Titan have such a fantastically low temperature yet with higher atmospheric pressure at the surface than the Earth does?

        • PeterMG says:

          Simply because it is so far from the sun its surface does not receive the same amount of energy in the first place. Look at our moon, blazing hot in the sun and frozen out of the sun. Very little atmosphere. But did anyone measure the temperature in the shadow of the Luna module I wonder? They must have done some experiments. If individuals were not so entrenched and could open their minds to the fact we are most likely wrong in science on a whole range of subjects we could perhaps have a sensible discussion. But I guess that’s not what Tony wants because he may have to do what I have done and have to reassess everything I thought I knew

    • wayne says:

      Patrick, most of what you said sound neat but you left out one prime variables that controls the environmental profiles, the gravitational acceleration… very key. You are speaking of Titan and its ‘g’ is but 1.35 m/s² to our 9.81 m/s² even though it has seven times the mass. Wrap that into the governing convection/subsidence equation of log(P / P0) / log(T / T0) − (g · M) / (R* · Γ) = 0 and you do need a lapse of less than 0.9 K/km near the surface to describe it’s lower T/P profile. Couple that with the fact that nearly 100% of the solar radiation energy (heat) is absorbed within the atmosphere itself on Titan and most high above and there are no conflicts with nature. Mass does primarily determine temperatures within an atmosphere all of the way to the surface, or, from the surface upward if you prefer.

      It kills me to hear arguments of why the earth’s surface temperature is not what is simply due to the amount of atmosphere. I can tell you have never really looked deep enough into that very subject to know the difference. Call that the GHE if you like, it is real. And that equation shows that Venus is no different that Earth of tropospheres just like Titan per Huygen or even Jupiter per Galileo probes.

  2. Patrick Hannon, Statistician says:

    That moon would be Titan

  3. philjourdan says:

    To set your place apart from all the pink houses on the street.

  4. Mike says:

  5. Abel Garcia says:

    The problem with that is most of the oxygen making trees and plants are located in the tropics.

  6. oldbrew says:

    ‘why would Titan have such a fantastically low temperature yet with higher atmospheric pressure at the surface than the Earth does?’

    It’s ten times further away from the Sun.

  7. mkelly says:

    Visibility 10.0 miles
    Clouds Mostly Cloudy 600 ft
    Overcast 2300 ft

    Windchill 26 °F
    Dew Point 25 °F
    Humidity 97%
    Rainfall 0.00 in
    Snow Depth Not available.
    UV 0.0 out of 12
    Pollen Not available.
    Air Quality Not available.
    Flu Activity

    For Point Barrow Alaska today.

  8. Latitude says:

    just for clarity…. 😉

    a greenhouse is literally a glass house…..as opposed to a shade house with shade screen

    In the tropics we use greenhouses to emulate the climate of the much higher latitudes…..
    …with chillers of course

  9. Charlie says:

    Did you mean, “solar insolation”? 🙂

  10. PeterMG says:

    By the way my Greenhouse is used to protect my plants from frost in the spring and to give some protection to tender vegetables is summer, not to make a humid tropical hothouse.

  11. Truthseeker says:

    The purpose of a productive greenhouse is to control conduction and convection to keep temperatures higher than they otherwise would be and to allow the pumping in of additional CO2 to improve plant growth.

    A greenhouse has always been a very bad analogy for a free-flowing planetary atmosphere.

  12. Robert of Ottawa says:

    During June, the Arctic receives more solar insolation than the tropics

    At the Arctic circle during summer solstice, the angle of incidence of insolation is 47 degrees. At the Northern tropic, it is 90 degrees; at the Southern tropic, It is 43 degrees. Therefore, this statement is incorrect.

    • The statement is correct. The Arctic receives 24 hours of sunlight in June, compared to 12 hours at the equator.

      • The important comparison is what is the solar insolation radiation energy actually absorbed by the surface per square meter per day at the arctic compared to that at say the Tropic of Cancer? Knowing the number of hours of daylight is highly inadequate. The arctic reflectivity is higher, atmospheric scattering and absorption is greater, and much of the daylight at the surface is much less bright.

  13. Baa Humbug says:

    Interesting post Tony.
    What do you mean by

    “During June, the Arctic receives more solar insolation than the tropics,”?

    Is that insolation at the surface or top of atmosphere?
    Thnx in advance

    • Peak solar insolation at the ground surface during midsummer is near the poles, because of 24 hour sunlight.

    • Baa Humbug says:

      According to Serreze and Barry 2005, the arctic experiences frequent cloud cover, exceeding 80% frequency over much of the arctic ocean in July.

      Now I’m trying to reconcile some of your previous statements I.e.
      “Cloudy and humid nights are warmer than clear and dry nights, largely because of the greenhouse effect”

      High insolation plus high cloud cover (greenhouse clouds that radiate back the high insolation) should lead to high (er) temperatures should it not? Yet Arctic temperatures barely reach above zero, in contrast tropics reach 30+

      Furthermore, if you are correct that the Arctic is cold because of lack of greenhouse gasses, do you have any pictures/documentations of Arctic glass structures with tomatoes and oranges growing in the arctic summer?

  14. KevinK says:

    Tony, you might want to read this, some folks at the Horticulture Department (at Penn State of all places) decided to test your hypothesis (i.e. “back radiation” affects the average temperature).

    They built some greenhouses with plastic film roofs/ceilings. Plastic films are preferred to glass these days; cheaper, tougher, easier to maintain, etc. Some with ceilings that are transparent to IR and some with “IR blocking films”.

    Click to access penn_state_plastic_study.pdf

    Bottom line is no observable (larger than the error bars) temperature difference, IR blocking or not.

    From the report; “High temperatures in the high tunnels (aka a greenhouse) covered by different films showed very similar trends in both years (Graphs 5 to 7), rising above outside temperatures, BUT SHOWING LITTLE DIFFERENCE among the film treatments”. “Little difference” means within the error bounds of the measuring instruments.

    This is empirical evidence, I do not work for these folks, have never even met them. They do not seem to have any dog in this AGW hunt and only seem to be figuring out how to grow bigger peppers, yeah for bigger peppers, I’m a fan of peppers, I love them stuffed.

    They did observe (on occasion) that the interior temperature was lower than the outside (ambient) temperature. They did not offer a reason why, I speculate that warmer air surrounded the greenhouse for a while and the response was not fast enough inside to allow the temperature to rise to meet the ambient temperature.

    It is all convection and conduction, radiation has nothing to do with determining the the average temperature inside a greenhouse. Response time is a different argument.

    Not my report, not my opinion, I do not suspect they adjusted their data, what purpose would that serve for them ? They are not selling the IR coated plastic films, they are just trying to help farmers.

    Cheers, Kevin.

    • There is no question that a glass greenhouse with a low roof is dominated by convection, but if you put heat lamps in, the IR will warm the plants – similar to how greenhouse gases do it.

      • KevinK says:

        There are no “heat lamps” mentioned anywhere in that report.

        They where specifically trying to determine the effect (if any) of IR blocking plastic “windows”. They did not detect any measurable effect. IR Transparent windows = same temperature as IR Opaque windows.

        If IR radiation from 50 feet away cannot make the temperature rise do you really expect that IR energy from 20,000 feet away can do it ? Do you understand the concept of “1/r squared” losses when dealing with diffuse light sources ?

        Cheers, Kevin.

  15. Mack says:

    It’s the angle of the sun on the surface Steve. Nothing to do with any “greenhouse” gases.
    The poles may get 24hrs / day of insolation but it comes like this…..

    That’s why it’s so cold at the poles. The sun drives the climate. Only in looney land does Co2 have anything to do with it.

  16. Bob Knows says:

    Even in summer the arctic sunshine is at a low angle while the equatorial regions are close to straight down all year. It has very little to do with how much moisture is in the air and nothing to do with how much CO2 is in the air.

    • For about one minute a day. For 18 hours a day, the sun is higher in the Arctic.

      • KevinK says:

        Tony, there was a guy (way back when ~1760) called Lambert, he figured out what happens when light arriving at an angle is absorbed by a surface. Or, conversely when light is emitted from a surface and you observe it from an off-axis angle. It is covered in all the undergraduate optical radiometry courses.

        http://en.wikipedia.org/wiki/Lambert%27s_cosine_law

        Cheers, Kevin.

      • PJ London says:

        Now the conversation is just getting silly. Please explain how, even at the summer solstice, the sun is higher at (say) 70 deg N than at the equator or anywhere in the tropics. Of course once the angle of incidence is taken into the equation then the energy per sq m calculation shows how silly this notion is.

        • Stop being stupid. The sun is at the zenith for one minute a day. It is below the horizon for 12 hours a day.

          I’m so sick of this crap.

        • Bob Knows says:

          Of course you are right PJ. The sun is close to vertical, (within 24 degrees) all year at the equator. I’ve watched the midnight sun on the Arctic Ocean that Goddard is talking about, and while its not dark, its does not provide the kind of solar heating, or lighting, that verticle or high angle sunshine provides. Even in summer the arcitc sun is less than 24 degrees from horizontal. The sunshine per area of land is much less than at the equator. This is so basic Goddard must be pulling our legs. .

        • The total solar insolation at the pole is higher on June 21 than in the tropics. One of the reasons the pole stays colder is because there is much less greenhouse effect there due to lower humidity

          Please stop being so incredibly obtuse. It is very discouraging for me to see this nonsense being repeated over and over and over again by skeptics.

        • PJ London says:

          Hey It is your site so I am going to stop now.

          But if you are seriously trying to tell me that the energy per unit area at the surface at the poles or in the Arctic circle, is greater than in the tropics, after the additional atmosphere that has to be penetrated plus the additional area owing to angle of incidence, regardless of the date, then I am not going to argue.

          I have looked up every reference to insolation I can find and find no data to support your position.

          Water and water vapour has the property of holding and releasing heat energy (hence a hot water bottle), and yes it acts in this manner in the atmosphere as well as in a rubber bottle.
          All it does is change the rate of heat transfer, it does not generate heat.
          Change of state (Vapour to water to ice) absorbs and releases heat from the environment. when vapor turns into dew or rain then heat is released. So does the surrounding environment get warmer when dew or rain forms, yes. But only when the Humidity is turned into liquid not vapour.
          When water evaporates into vapor, then heat is taken from the surrounds and stored in the water as energy (not heat).
          So a change of state will affect the surrounds and a difference in the rate of heat transfer is observable in water and water vapour.
          If that is the Greenhouse effect, then I concur and we can stop the discussion, if there is any other physical property I am unaware of please enlighten me.

        • How much solar energy does the equator receive during the 12 hours of night on June 21?

  17. Paul Clark says:

    It seems the tables are turned, and now Mr Heller’s part of the orthodox “consensus” on the greenhouse effect, chastising “slayer” skeptics of the theory:

    I don’t concur with this conformism; it’s good to disagree, even about basic things like the greenhouse effect. It’s characteristic of skeptics to be disorganised, disagree, and not speak from the same script.

  18. Bob Knows says:

    The fabled “greenhouse effect” was disproved by experimental physics more than a century ago. Greenhouses get warm by blocking air circulation, not by reflecting heat. The “greenhouse effect” is popular fiction by people who have not done the science for glass or plastic greenhouses, and has NEVER been demonstrated to work on a whole planet.

    • KevinK says:

      Also, a Dr.Nasif Nahle recently (2011) repeated Dr. Wood’s work and disproved the “greenhouse effect”;

      Click to access Experiment_on_Greenhouse_Effect.pdf


      .
      Perhaps Tony can pay him a visit ?

      • Not interested in bullshit

        • KevinK says:

          Tony, with respect, R. W. Wood did quite a bit of pioneering physical optical work a century ago. Lots of references to his work regarding diffraction, scattering, and other basic optical principles are hidden in the footnotes of more modern optical textbooks. He was far from a charlatan. While you may not believe his observations RE the “greenhouse effect” you might want to at least replicate his work and find the errors (if any). Dr. Nahle did exactly that and got the same results.

          Lots of “IR” phenomena where first observed/explained by R. W. Wood, I do not think you have relevant standing to dismiss his work as BS. Of course he did not have access to a computer, but does that matter ?

          Cheers, Kevin.

  19. slimething says:

    Seems pretty simple to me:
    http://www.weatherquestions.com/Why_are_deserts_so_hot.htm

    Why are deserts so hot?
    Deserts are hot primarily because of a lack of water. When the sun shines on the ground, all of the absorbed sunlight goes into raising the ground’s temperature. If there was moisture in the soil, much of this heat would go into evaporation of some of the water, which requires heat to accomplish, and thus keeping the soil cooler that it would otherwise be. This cooling is from the “latent” heat of evaporation that is required to change liquid water into water vapor, and is the same reason why water evaporating from your skin feels cold.

    Associated with the lack of water is a lack of vegetation, which would also cause water to evaporate as part of photosynthesis — a process called evapotranspiration.

    The common perception that deserts are hot because of the bright sand is incorrect. Since vegetation is darker than most desert soils, if a desert could have vegetation that didn’t need water to live, the desert would actually be hotter since it would absorb more sunlight. Instead, the vegetation causes water to evaporate (and uses some of the sunlight for other plant growth process). Similarly, if deserts were covered by dark soil rather than light soil or sand, they would also be hotter.
    Interesting facts:
    DESERTS ARE COLD AT NIGHT:Because of the lack of water in the ground, and little water vapor in the air, most deserts can get quite cool at night. This is because (1) dry ground does not retain as much heat as moist ground, and (2) water vapor is the most important greenhouse gas, so dry air allows the surface to cool rapidly at night through loss of infrared radiation to outer space.

    In fact, it has been calculated that the Sahara Desert actually loses more infrared radiation than it gains solar radiation from the sun. This net loss of radiant energy is balanced by the sinking air over the desert, which warms as it is compressed. The air over the desert is, in turn, being forced to sink by rising within rain systems hundreds or thousands of miles away. Thus, in some sense, rain can be considered the cause of deserts(!).

  20. Gail Combs says:

    Just some information:

    RACookPE1978 says: @ February 18, 2014 at 8:11 pm
    http://wattsupwiththat.com/2014/02/17/crises-in-climatology/#comment-1571641
    Gail:

    What you want to look at is the column below called “Direct Radiation Horizontal Surface”.
    Those are radiation received on the equinox for solar radiation at each latitude at noon.

    I’m going to duplicate below a “spreadsheet copy” of a spreadsheet I have for all latitudes for the actual radiation on to a horizontal surface at 12:00 on that “average” 342 watts/meter^2 day. Remember, top-of-atmosphere radiation is going to vary over the year from 1410 (high, on January 3) to the 1320 (the “low” value on July 3 each year). This is for a day in mid-September, near that “average” value on the equinox at time of minimum Arctic sea ice extents….

    Go to the link to look at the spread sheet of the actual solar radiation “on to a horizontal surface at 12:00 on that “average” 342 watts/meter^2 day.”

    Here is a chart of the insolation by latitude by month:

    • Baa Humbug says:

      Thnx Gail. I tried to post that graphic on another thread.

    • KevinK says:

      Yep, just integrate the area under the curve (which has been corrected per Lambert’s “rule”) and you see that the poles get a little bit more solar energy for a few months, but have a huge deficit when considering the entire year.

      And the term “solar insolation” (like most things related to optical radiometry) is often abused and misunderstood. You can find definitions of “insolation” that correct for the angle of the surface and others that do not. “Onto a horizontal surface” is the key phrase here.

    • Mack says:

      That’s a very interesting set of graphs Gail . That would be from satellite data.? What I would like you to do now is calculate the AVERAGE of these graphs over that year. You too Steve. Presumably there would be a mirror image of this for the southern hemisphere but we only need to deal with one hemisphere for this calculation. Just eye-balling those graphs I would say it would be about 340W/sq.m average per year?

      • Mack says:

        Oh hell , I didn’t even bother to read all the stuff above the graphs…..there it is! in black and white…..average 342 watts/sq.m /day/year

  21. Beale says:

    Other things being equal, during the daytime the solar insolation per unit of surface area is proportional to the sine of the elevation of the sun above the horizon. Working this out we see that while it is true that around the summer solstice the insolation at the North Pole is greater than at the equator, averaging over the whole year the former is only about 40% of the latter.

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