Reader Quiz

Which location has more water vapor in the air?

  • Location A – 90% relative humidity
  • Location B – 20% relative humidity

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31 Responses to Reader Quiz

  1. Les Johnson says:

    You could also ask which area has more water vapour:

    1. The arctic with 20% RE
    2. An equatorial desert with 20% RE

    the tropopause is about 1/2 as deep at the arctic as the equator. Thus, the “container” is smaller.

    In your example, Area A vs Area B, Area A would have about 4.5 times the water per unit volume, but about 9 times the amount of the GHG in the tropopause.

  2. Martin says:

    depends on the temperature – clue is the word “relative”

  3. Depends on the temperature at point A and Point B because it’s relative humidity. The RH tells how much of the air is saturated at a given temperature. There is more water vapor in the air at 100 degrees when the humidity is at 20% than at 100% humidity at temperature of 25 degrees.

    • Was that more than you wanted?

      • That was exactly what I was looking for. The point being that I didn’t provide enough information to answer the question.

        • wayne says:

          And isn’t that, the missing information statements and claims, what you see streaming from the AGW alarmist side’s propaganda (and also sadly within some other climate blogs on both sides)

          I think I see your point SG, everyone needs to look more carefully and deeper into what is daily being said to you. Find out the truth yourself but it takes some time and digging about.

  4. kentclizbe says:

    Riyadh, Saudi Arabia:
    114 F with 14% relative humidity
    Absolute humidity, kg/m3: 0.009

    88 F with 80% relative humidity
    Absolute humidity, kg/m3: 0.026

    So the amount of “greenhouse gas,” water, in Singapore at 88F is triple the amount of “greenhouse gas” in the air in Riyadh at 114F.

    Yet, Riyadh is nearly 30F hotter than Singapore.

    Seems like that “greenhouse gas,” water, is actually cooling the air in Singapore.

    Or am I missing something?

    • Vegetation and bodies of water act as an evaporative cooler during the day. I’ve been in the Utah desert when it was 105 during the day, and 40 at night. Low humidity/little vegetation

      Greenhouse effect is most noticeable at night.

      Also, H2O is like CO2 – its effect tails off with increasing quantities,

      • MarkU says:

        When you say “greenhouse effect”, are you simply referring to the phenomenon of slower cooling at night in areas with more moisture in the air without reference to a cause, or are you ascribing the cause as the IPCC version of “greenhouse effect” that the “greenhouse gases” in the air literally reheat the earth by absorbing and re-reflecting heat in the form of “long wavelength” energy back to the earth?

      • PeterMG says:

        And I have been in Riyadh during the day when it was 50 C and there is no way it dropped much below 40 C at night. And to illuminate the heat Island effect I was unfortunate enough to have to visit Buraydah on several occasions and the same phenomenon was experienced there. Yes the Arabian desert gets cold in the winter, but not to the extent that people imagine. The places that do get very cold are those that are at an altitude where the thinner atmosphere loses it heat much faster and there is plenty of elevated areas around in Arabia.

        • What was the dew point?

        • kentclizbe says:

          Looking at average readings in Riyadh, in August, the hottest month:

          Relative humidity: 14%
          Maximum temperature: 114 F; absolute humidity kg/m3: 0.009; dew point 53 F
          Minimum temperature: 95 F; absolute humidity kg/m3: 0.006; dew point 39 F

          Don’t these numbers show that lack of water vapor in the air causes greater temperature swings, and is hotter temperatures than places where there is more water vapor in the air?

        • Kent,

          Those numbers don’t work, because the relative humidity rises as the temperature drops. Think of the dew point as being constant during the day.

        • Chip Bennett says:

          A metaphor:

          The air = a sponge
          Absolute Humidity = amount of water in the sponge
          Temperature = hand squeezing the sponge (the tighter the squeeze, the lower the temperature)
          Relative Humidity = the sponge’s total water-holding capacity at the given squeeze pressure
          Dew point = the squeeze pressure at which water comes out of the sponge

  5. philjourdan says:

    Location C – the little mermaid’s home.

  6. Anything is possible says:

    This is a very useful tool for your humidity-related conversions :

    Converting known values of RH and temperature into ppmv is particularly revealing when compared to atmospheric levels of CO2.

  7. Goodmongo says:

    And I’ve been in places where it was way warmer at night. This is all stupid because there is not enough other information. Weather changes daily and hourly. If wind isobars compact it causes friction that can have a way larger effect than the GHG present. Most of what has been posted lately about GHG effect is childish.

    Yes it impacts things. But it’s impact can be way less than other factors.

  8. Timo Soren says:

    Explicit example: 20% Relative Humidity at a temp of 37 C, means that the total water vapor in a volume(V) of air is V(m^3)*44 (g/m^3) *.20 = 8.8*V (g)
    90% Relative Humidity at temp of 5C means the total water vapor in a volume(V) of air is
    V (m^3) * 6.8 (g/m^3)*.9 = 6.1*V (g) and obviously for any V : 8.8V > 6.1V

  9. Timo Soren says:

    BUT: If we had compared 20% at 20C and 90% at 5C then the the calculation results in
    V(m^3)*17.3 (g/m^3)*.20 = 3.46V(g) and V(m^3)*6.8 (g/m^3)*.9 = 6.1V(g) and it is reversed.
    6.1V(g) > 3.46V(g) so one CAN’t conclude from the relative Humidity the answer.

  10. Chip Bennett says:

    Not enough information; but that’s been answered already.

  11. skience says:

    At standard temperature and pressure the answer is obvious …

    But even very hot steam in a near vacuum has less water …

  12. Whatever the answer is, I’m sure it’s being caused by anthropogenic global warming and it will only get worse unless we spend trillions of dollars to do something about it.

  13. The key is in the word “locations” for A and “location” for B. How many locations for A? If it’s 2 or 3 locations, they may still have less water than B, but if it’s 10000 locations, then I would go with A.

  14. bleakhouses says:

    Water v air in re conductivity. Easy experiment. Stick your hand in a 200 deg. oven. Stick your hand in a 200 degree pot of water. You learn quick about how good a conductor water is.

  15. nickreality65 says:

    Depends on the dry bulb temp. For constant grains per pound dry, air at 50 F 90% becomes 20% at 94.4 F. Same grains/lb. Trane’s web site under commercial charts and tables has a great interactive psychrometric chart from Handsdownsoftware.

  16. Bob Knows says:

    It depends on the temperature of the air.

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