Urban Warming – There is More To It Than Just A Heat Island

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The descriptions of urban warming dwell on the heating of the air by the local infrastructure. There is more to it than simple conduction to the air mass from warmed surfaces.

In the far infrared, where the peak radiation wavelength is determined by the temperature, much of the energy from warmed surfaces is absorbed by the greenhouse gases in the atmosphere within a meter or so. These gases then re-radiate to any other nearby surfaces or gases further away and conduct by collisions with other air molecules to heat the air. There are also windows in the infrared spectrum that let warm surfaces radiate directly to other surfaces. Thus for a temperature measuring instrument, the temperature measured is a combination of the air temperature conducted to the thermometer by air flowing past it and IR heating from nearby surfaces. This is why in the polar regions when measuring very low temperatures, a person approaching the thermometer will raise the temperature reading.

This second source of increased temperature causes “urban warming” even where the location is strictly rural. A measuring station at an isolated research station or farm can have “urban warming” when the thermometer is in close proximity to just one heated building.

perry-ok-ushcn-visible-and-infrared-1

Figure 1 is a visible and FLIR IR image of the MMTS station at the Perry, Oklahoma Volunteer Fire Department. The image is from an article by Anthony Watts here, used by permission.

Painting the MMTS white only reduces direct heating by sunlight at visible wavelengths. In the long wavelength IR, any paint, black, white, or any other color, has the same emissivity, more than 0.9, and will absorb IR equally well. In Figure 1, the west-facing uninsulated door is very warm compared to the north-facing wall. It is being heated both by the sun and the building interior. The MMTS is slightly warmer (perhaps 2 or 3 degrees) than the mounting pipe. The pipe is unpainted, somewhat shiny, with a lower emissivity, reflecting more of the IR. Thus it appears black, where the MMTS is a warmer dark purple.

Pierre has posted on a German study of the temperature shifts with the installation of electronic thermometers here. This shift is due to the different way a glass thermometer in a wooden shelter responds to IR in the vicinity and the way a compact modern MMTS responds. There is also the issue of the need for cabling that leads to a distance bias to the nearest building.

Every weather station should be checked for IR emissions in the “view-shed”, the surrounding surfaces and buildings. This should be done at several hours of the day, to catch sunlight warming all the surfaces, and internal building heating variations.

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13 responses to “Urban Warming – There is More To It Than Just A Heat Island”

  1. Graeme No.3

    There are ways of reducing IR absorption, even for paint.
    20 years ago the company I was working for had 2 large tanks exposed to the sun for up to 8 hours a day. They painted both white but for one tank the paint incorporated hollow ceramic spheres. This alone reduced the temperature increase by over 0.5℃.
    There are also IR reflecting pigments, quite often greens or browns, which have uses for defence equipment. Rather expensive for large objects, but I expect quite acceptable IF the object is to get an accurate reading.

  2. Richard111

    I am at a loss here. This implies that ‘greenhouse gases’ DO NOT WARM BY CONDUCTION in the local atmosphere! Science tells me CO2 gas will be at local air temperature and radiating over the 13 to 17 micron band. Assume the surface is at 15C it will be radiating at some 400w/m^2 of which some 18% of the total energy will be in the 13 to 17 micron band. There will be minimal absorption of these bands by both the surface and the CO2 in the air above. BUT IT WILL REDUCE THE RATE OF COOLING OVER THESE BANDS FOR BOTH THE SURFACE AND THE CO2. A reduction in the rate of cooling is not a warming!

    1. DirkH

      “Assume the surface is at 15C it will be radiating at some 400w/m^2 of which some 18% of the total energy will be in the 13 to 17 micron band.”

      I will assume that you have looked that up correctly.

      ” There will be minimal absorption of these bands by both the surface and the CO2 in the air above.”

      Help me here. I don’t understand. Surface will absorb any frequency partially, as a greybody, and reflect the rest; independent of whether or not that emission will later be absorbed by anything.

      ” BUT IT WILL REDUCE THE RATE OF COOLING OVER THESE BANDS FOR BOTH THE SURFACE AND THE CO2. ”

      What will reduce radiative cooling of a greybody? Are you now talking about backradiation, or back-conduction?

      1. Richard111

        The surface and CO2 in the atmosphere are both radiating in the 15 micron band. Don’t worry about grey bodies, we are discussing a finite band of radiation from two sources. The only requirement is that both sources are capable of absorbing/emitting said band of radiation. Since both sources are at some temperature ABOVE the peak temperature for the 15 micron band neither source can absorb over that band. It is statistically possible for either source to absorb an in band photon having just emitted a similar photon and this makes no difference to the energy in the source. Energy out equals energy in. This delays the radiative cooling of the source. Since the INTENSITY of the surface radiation is higher than the intensity of the CO2 in the atmosphere, which must radiate in 360 cubed degrees, the delay is more effective in the CO2. The CO2 in the atmosphere CANNOT increase in temperature until the altitude temperature has cooled to about -30C (243K).

        1. DirkH

          ok, thanks.

    2. Mike Heath

      I thought the greenhouse gas idea was about back-radiation not conduction, though as I understand it the real greenhouse is warmed mostly by convection.

  3. A C Osborn

    I am beginning to that we should stop worrying about UHI and other problems with thermometers etc and not bother to have input in to any so called Global parameters to do with Climate.
    The local weather is what needs to be monitored for where people live to give them meaningful warnings about their weather when required.
    The Global Temperature is an irrevalance developed by the Warmist Brigade to try and prove CO2 drives the climate.
    The climate is going to prove the them wrong over the next 10 years.

  4. Squildly

    @Richard111,

    “A reduction in the rate of cooling is not a warming!”

    EXACTLY!! … The atmosphere does NOT “Pile Heat” http://climateofsophistry.com/2015/01/21/atmosphere-not-insulation/

  5. cementafriend

    Some very good points Ed but you are wrong about CO2 absorbing IR
    my point at http://wattsupwiththat.com/2015/01/29/a-sin-of-commission/ on 31st Jan was –
    cementafriend
    January 31, 2015 at 5:43 am

    If one considers the equation for radiation absorption developed by Prof Hoyt Hottel at MIT (eg equation 5-145 in the Chemical Engineering Handbook) it can be determined that absorptivity of CO2 in the atmosphere at the present level is so small to be unmeasurable. The suggestion that CO2 contributes 20% to the total of so-called greenhouse gases is nonsense, Firstly, some 30% of the sun’s radiation that gets to the earth’s surface (of which about 70% is water surface, plus another large amount that is covered by some snow and ice at least for part of the year) is radiated directly to space particularly at night. Secondly, of the remaining 70% some 90% or more is radiated to space by water vapor, and water drops+ice particles in clouds. The temperature of the atmosphere comes from convective transfer of heat from the surface and from the phase change when water vapor condenses and freezes to form clouds. CO2 contributes to the radiation to space but this is not due to the IR absorption. It is due to convective exchange with other gases in the atmosphere and is at an average temperature of 220K to space at 4K. .As indicated CO2, so-called “greenhouse”, contribution is not measurable.
    Next one needs to look at the many measurements (from balloon and ground stations) of CO2 in the atmosphere over 150 years and in ice cores. It has been found that CO2 lags temperature over the progress of one day (lag about 1hr), over a week, over a month, over a year, over cyclical periods of 60 years (lag upto 5yrs), and in ice cores by some 800 years. over long periods. This is measured proof that CO2 makes no “greenhouse” contribution.
    Maybe, you do not know Prof Hottel – look at his book on Heat transfer by Radiation, or his sections in Marks Mechanical Engineering Handbook and in Perry’s Chemical Engineering Handbook on Heat Transfer. Hundreds of Thousands of engineers have reviewed these and used them as references for actual practice of furnace design and evaluation. Physicists and so-called Climate Scientists play around with distorted theory while engineers rely on measurements and actual experience.

    1. Mike Heath

      Is it reasonable to say that CO2 vary with temperature very day with the lag of 1 hour, and then say the ice cores have a lag of 800 years?

  6. cementafriend

    Ed, I did not say that CO2 does not absorbs IR I said that it is so small that it is unmeasurable. Hottel’s equation includes the factors of path length and partial pressure. If you put in one metre as the path length then the absorptivity has many zeros after the decimal. The absorptivity becomes larger if you put in ten kilometers but note that at further distances from the surface the partial pressure reduces. The result is that the absorptivity is still too small to be measured. It should be obvious and is also generally accepted that that any molecules of CO2 which are more than 5 or 8 km from the surface and are at a considerably lower temperature than the surface will radiate to space. After, the molecules have radiated energy their temperature will be lower, they will then have the possibility of being heated by collision with other molecules such as oxygen and nitrogen. This latter is much more significant than IR absorption from the surface. Many say that CO2 helps to cool the planet but this is a bit of an exaggeration as the effect of CO2 is minimal even if the concentration (or partial pressure) in the lower atmosphere was ten times as high as present.

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