Back Radiation and Thermodynamics

The following picture is from Kiehl and Trenberth [1]

The above figure shows ‘back-radiation’ of 324 W/m2.  The value ~324 W/m2 would seem implausible as it is comparable in magnitude to the radiance from the sun! If it exists why cant it be used as an energy source.

If the atmosphere radiates 324 W/m2 downward it must radiate the same upward. But the Earth only receives 235 W/m2 nett radiation from the Sun (342 W/m2 – 107 W/m2 reflected).

This back-radiation is impossible – it defies the first law of thermodynamics – energy must be conserved – there can not be more energy leaving a body than what is coming in (when in equilibrium).

If this figure was true it would mean more energy is radiated from the Earth then it receives.

“Backradiation” is the heat flowing from the cold atmosphere to the warm Earth – this also defies the Second Law of Thermodynamics. Some will say that as long as the nett flow is from cold to hot all is OK. However the figure shows a flow of 324 W/m2 from cold to hot. This is purely imaginary. What the value indicates is the heat that would flow from the atmosphere to a body at a temperature of  zero K (-273 deg C)  if the atmosphere was a blackbody (emissivity = 1). The atmoshere is not a ‘blackbody’ and the Earth is not at zero K!

Similarly, the 350 W/m2 upward heat flow is the theoretical radiation from a blackbody at the temperature of the Earth’s surface to a body at zero K.

There is no evidence that ‘back-radiation’ exists – it has ever been detected or measured.

This is an obvious error – how did this get past the peer review process. Why is this figure still being used to explain the Earths energy balance without questioning. Why are we spending vast amounts of money solving a problem based on this flawed hypothesis?

This is basic physics. It is in error.

How much heat is lost from the Earth’s Surface by Radiation?

By subtracting this ‘backradiation’ value (324 W/m2) from the upward radiance (390 W/m2) gives a nett surface irradiance of 66 W/m2 upward. This is less then the convective heat loss from the surface of the Earth (102 W/m2).

In summary:

  • The Energy budget of Kiehl and Trenberth violates the laws of thermodynamics.
  • The Earths surface loses more heat from convection (102 W/m2) then by radiation (66 W/m2)

[1] Kiehl, J. T., K. E. Trenberth, 1997: Earth’s Annual Global Mean Energy Budget. Bull. Amer. Meteor. Soc., 78, 197-208

4 Responses to Back Radiation and Thermodynamics

  1. iya says:

    There is no violation of the first law, if you consider solar and convection:
    in = 168+324 = out = 24+78+390 = 492

    The back-radiation does exist and can be measured.

    It does violate the second law, though to postulated that the energy emitted by the surface gets back-radiated by the atmosphere and then WARMS the surface.

    The actual mechanism for the warming is actually found in the laps rate.

    • wstannard says:

      Thank you for your comment Iya.. (one of the first to my blog)

      Would you please have another look at that 324 W/m2 which is supposedly radiated by the atmosphere downward to the Earth’s surface. Surely there must also be 324 W/m2 radiated upward into space? (or does the atmoshere just radiate in one direction, downward from cold to hot).
      Add this 324 to the 107 W/m2 reflected from the surface and atmosphere and you have much more energy leaving the planet than energy coming in!

      That I think is a violation of the first law. So which figure is wrong?

      Look forward to your response..


    • markus says:

      “The actual mechanism for the warming is actually found in the laps rate.”

      Well, it is a dynamic system, and it can be postulated the increase in GHG causes additional back radiation to the earths natural equilibrium, because the thermodynamic nature of earths cooling is affected by the additional energy (photons) in the troposphere, slowing the lapse rate.

      Personally I don’t buy it. There seems to be no allowance in the theory for, not only the increase in pressure, but the expansion of the atmosphere and its ability to hold a higher temperature away from the earths surface into the upper troposphere.

  2. Radiation, convection, conduction can only move from high temperature to low temperature. The lower troposphere is -40 F or C. The S-B radiation at -40 F is half that of the surface radiation. This GHG/back radiation perpetual motion loop is bogus. The 2 W/m^2 of CO2 RF is lost in the overall magnitude and flux uncertainties.

    Prior to MLO the atmospheric CO2 concentrations, both paleo ice cores and inconsistent contemporary grab samples, were massive wags. Instrumental data at some of NOAA’s tall towers passed through 400 ppm years before MLO reached that level. IPCC AR5 TS.6.2 cites uncertainty in CO2 concentrations over land. Preliminary data from OCO-2 suggests that CO2 is not as well mixed as assumed. Per IPCC AR5 WG1 chapter 6 mankind’s share of the atmosphere’s natural CO2 is basically unknown, could be anywhere from 4% to 96%. (IPCC AR5 Ch 6, Figure 6.1, Table 6.1)

    The major global C reservoirs (not CO2 per se, C is a precursor proxy for CO2), i.e. oceans, atmosphere, vegetation & soil, contain over 45,000 Pg (Gt) of C. Over 90% of this C reserve is in the oceans. Between these reservoirs ebb and flow hundreds of Pg C per year, the great fluxes. For instance, vegetation absorbs C for photosynthesis producing plants and O2. When the plants die and decay they release C. A divinely maintained balance of perfection for thousands of years, now unbalanced by mankind’s evil use of fossil fuels.

    So just how much net C does mankind’s evil fossil fuel consumption add to this perfectly balanced 45,000 Gt cauldron of churning, boiling, fluxing C? 4 Gt C. That’s correct, 4. Not 4,000, not 400, 4! How are we supposed to take this seriously? (Anyway 4 is totally assumed/fabricated to make the numbers work.)

    IPCC AR5 attributes 2 W/m^2 of unbalancing RF due to the increased CO2 concentration between 1750 and 2011 (Fig TS.7, SPM Fig 5.). In the overall global heat balance 2 W (watt is power, not energy) is lost in the magnitudes and uncertainties (Graphic Trenberth et. al. 2011) of: ToA, 340 +/- 10, fluctuating albedos of clouds, snow and ice, reflection, absorption and release of heat from evaporation and condensation of the ocean and water vapor cycle. (IPCC AR5 Ch 8, FAQ 8.1)

    IPCC AR5 acknowledges the LTT pause/hiatus/lull/stasis in Text Box 9.2 and laments the failure of the GCMs to model it. If IPCC can’t explain the pause, they can’t explain the cause. IPCC GCMs don’t work because IPCC exaggerates climate sensitivity (TS 6.2), of CO2/GHGs RF in the power flux balance and dismisses the role of water vapor because man does not cause nor control it.

    The sea ice and sheet ice is expanding not shrinking, polar bear population is the highest in decades, the weather (30 years = climate) is less extreme not more, the sea level rise is not accelerating, the GCM’s are repeat failures, the CAGW hypothesis is coming unraveled, COP21 turned into yet another empty and embarrassing fiasco, IPCC AR6 will mimic SNL’s Roseanne Roseannadanna, “Well, neeeveeer mind!!”

    One can only hope that 2016 will be the year honest science prevails. In the meantime the hyperbolic CAGW hotterist’s hysteria will continue to fleece the fearful, neurotic and gullible, (i.e. the world’s second oldest profession).

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