Proposed Experimental Method to Determine the Radiant Influence of CO 2 in the Night Sky Brian G Valentine US Department of Energy Washington, DC March 9, 2009

Proposed CO 2 Legislation: Based on What Evidence? A “consensus” view of the climate – yet without direct empirical evidence that CO 2 has a discernable influence A “consensus” view of the climate – yet without direct empirical evidence that CO 2 has a discernable influence To many people, CO 2 is the only factor that influences the global climate (?) To many people, CO 2 is the only factor that influences the global climate (?) EPA cannot regulate what it cannot measure. If there is a viable method to measure CO 2 influence, every attempt should be made to measure it. EPA cannot regulate what it cannot measure. If there is a viable method to measure CO 2 influence, every attempt should be made to measure it.

Theoretical consequences of “greenhouse” effect has yielded little empirical information “Hot Spot” near tropopause – gone unseen “Hot Spot” near tropopause – gone unseen Santer et al. (Proc Nat Acad Sci 2007) claimed “higher” humidity worldwide – but MOE much larger than effect claimed to be discerned Santer et al. (Proc Nat Acad Sci 2007) claimed “higher” humidity worldwide – but MOE much larger than effect claimed to be discerned Santer (2004) – predicted lowering of tropopause – has not been observed. Santer (2004) – predicted lowering of tropopause – has not been observed.

Is any other empirical evidence of “greenhouse” effect available? Standard model of “greenhouse” effect predicts CO 2 radiant “forcing” at the tropopause Standard model of “greenhouse” effect predicts CO 2 radiant “forcing” at the tropopause “Feedback” effect is on water vapor “Feedback” effect is on water vapor Water accumulation in the atmosphere is predicted at ~constant rh Water accumulation in the atmosphere is predicted at ~constant rh Terrestrial influence of CO 2 radiation is minimal. Terrestrial influence of CO 2 radiation is minimal.

Can any radiation from CO 2 be resolved at ground level? Depends on atmospheric conditions Depends on atmospheric conditions If rh near ground level is “low,” the Earth emits at 15+ μm to space, cooling the Earth– If rh near ground level is “low,” the Earth emits at 15+ μm to space, cooling the Earth– A portion of the re-radiation is (assumed to be) absorbed by CO 2 and emitted A portion of the re-radiation is (assumed to be) absorbed by CO 2 and emitted Most of the CO 2 emission overlaps water spectrum Most of the CO 2 emission overlaps water spectrum A small fraction of CO 2 emission does not overlap water absorption spectrum (amount subject to interpretation) A small fraction of CO 2 emission does not overlap water absorption spectrum (amount subject to interpretation)

Can CO 2 Radiation be Resolved? I calculate 0.02 W m -2 maximum downward unencumbered emissive power from CO 2 radiation near the tropopause in the night sky I calculate 0.02 W m -2 maximum downward unencumbered emissive power from CO 2 radiation near the tropopause in the night sky Attenuated to O (E-04)-O (E-03) W m -2 at ground level through a “clear” atmosphere; rh~20% Attenuated to O (E-04)-O (E-03) W m -2 at ground level through a “clear” atmosphere; rh~20% losses are primarily due to scattering (density variations giving rise to natural convection are a challenge to account for) losses are primarily due to scattering (density variations giving rise to natural convection are a challenge to account for)

Can downward directed CO 2 Radiation in the Night Sky Be Observed? Water evaporation rate by radiation cooling into clear night sky – depends on temperature, surface area exposed, rh of surrounding air, wind convection (if any), and emissivity Water evaporation rate by radiation cooling into clear night sky – depends on temperature, surface area exposed, rh of surrounding air, wind convection (if any), and emissivity Small portion (~10%) of water emission spectrum overlaps unencumbered CO2 radiation Small portion (~10%) of water emission spectrum overlaps unencumbered CO2 radiation

Can downward directed CO 2 Radiation in the Night Sky Be Observed? That portion of water emission spectrum overlap with quantized CO 2 radiation would encumber water evaporation over that wavelength range That portion of water emission spectrum overlap with quantized CO 2 radiation would encumber water evaporation over that wavelength range Total power possibly influencing water evaporation is TINY – implies that a very large surface area needed to observe effect at all Total power possibly influencing water evaporation is TINY – implies that a very large surface area needed to observe effect at all

Can downward directed CO 2 Radiation in the Night Sky Be Observed? To discern the influence of downward radiation from CO 2 by water evaporation in the desert at night. Large area, shallow water troughs could be filtered for radiation wavelengths of interest, and unfiltered. To discern the influence of downward radiation from CO 2 by water evaporation in the desert at night. Large area, shallow water troughs could be filtered for radiation wavelengths of interest, and unfiltered. The evaporation process would be monitored at night – repeated measurements over long time intervals needed to observe a cumulative effect The evaporation process would be monitored at night – repeated measurements over long time intervals needed to observe a cumulative effect

Difficulties with the Proposed Experimental Method Difficulty constructing selective wavelength filters and diathermanous covers for troughs (probably only ~50% selectivity achievable in practice) Difficulty constructing selective wavelength filters and diathermanous covers for troughs (probably only ~50% selectivity achievable in practice) Difficulty accounting for background influences Difficulty accounting for background influences Difficulty monitoring such a large area for a long period of time Difficulty monitoring such a large area for a long period of time

Errors Associated with the Proposed Experimental Method Changing conditions from night to night may influence radiation of interest differently Changing conditions from night to night may influence radiation of interest differently At best, only about mm difference in evaporation from 5 mm initial water depth would be observed, per Ha of exposed surface area. This is probably within MOE of random influences. At best, only about mm difference in evaporation from 5 mm initial water depth would be observed, per Ha of exposed surface area. This is probably within MOE of random influences.

Proposed method would require years of study The random influences on water evaporation from unencumbered troughs would have to be studied first – to gain an understanding of the magnitudes of random errors The random influences on water evaporation from unencumbered troughs would have to be studied first – to gain an understanding of the magnitudes of random errors Cannot assume upper atmospheric conditions are the same over large areas in the desert night Cannot assume upper atmospheric conditions are the same over large areas in the desert night

Are any other experimental methods possible? Saturation of blue from horizon to zenith in daytime sky may change over time as a result of water vapor and CO 2 Saturation of blue from horizon to zenith in daytime sky may change over time as a result of water vapor and CO 2 Similarly, saturation of red at horizon in the sky at evening may change over time Similarly, saturation of red at horizon in the sky at evening may change over time These are, however, fourth and sixth order effects in reciprocal wavelength, respectively These are, however, fourth and sixth order effects in reciprocal wavelength, respectively Paper on all this in preparation Paper on all this in preparation

Acknowledgement Special thanks to Special thanks to George E Smith, George E Smith, New Zealand New Zealand