Water Vapor Feedback

[HailMan06]

Let us address feedback of any kind, positive water vapor feedback and the impossibility of feedbacks in a climate system limited by its energy, the sun.

The 1/(1-f )equation which is too often quoted for both positive and negative feedback aficionados does not apply to to the climate system. It applies to a an electronic amplifier with an independent , well regulated power supply to provide power which the amplifier with its feedback is controlling.

The climate system when discussing the effect of adding CO2 to the atmosphere bears little relationship to a feedback amplifier. First there is no well regulated power source. The power is supplied by the sun and in this limited case is a constant. The power source thus is analogous to a circuit with a limited power available having an internal impedance, unregulated source, of energy which is determined by the surface characteristics mainly of the ocean and the wind/wave modulation of the thermal impedance of its surface/atmosphere interface. Any atmospheric effect (lower temperature) which would allow more energy(mostly in the form of water vapor) to flow from the surface will lower the temperature of the surface because of its thermal impedance and thus has a self limiting (negative feedback) energy source. The vague concept of additional water vapor increase in the boundary layer intercepting more IR and re radiating it to the surface to cause more evaporation is a non-starter. Anything which raises the surface layer temperature of the atmosphere reduces the temperature gradient and thus limits(negative feedback again) the flow energy from the source, the surface volume. Stated more fundamentally; the source of energy is the surface volume , there is no source of energy in the atmosphere to evaporate more water vapor, the source of energy is the surface itself. any energy in the atmosphere must come from the surface itself. It would be equivalent to a high impedance power source driving energy into a restrictive load and thinking the increase in voltage appearing in the load would some how extract more current from the source which is already limited by the current which it can drive into the load by its own impedance and the impedance of the load.

Is there any CO2 greenhouse effect? The latest (4th) conjecture put forth by the IPCC consists of doubling the thickness of the CO2 blanket which causes the final radiation of the cO2 spectrum to be emitted into space from a higher altitude. If this occurs in the 6.5C/km lapse rate portion of the atmosphere, it would radiate less power and force the earth atmosphere and therefore the surface temperature to rise. (I keep looking and would like to find a study which shows that the radiation altitude change takes place in the troposphere ie the atmospheric temperature lapse rate rather than the tropopause..or even above in the stratosphere) The following discusses the effect on the earth climate if this conjecture is correct.

Exploring the IPCC AR-5 CO2 Greenhouse (Yes Virginia, there may be a greenhouse effect)

Introduction

Theme:

Doubling CO2 which may have an IR blanketing effect on the upper atmosphere adds no energy to the earth system and therefore will cause essentially no change in the shape and function of the natural random chaotic atmosphere in balancing a constant solar energy input with the IR radiative output to space.

Assuming the latest 'greenhouse' conjecture put forth by the IPCC specifically; that the increase altitude at which the CO2 portion of the IR spectrum is colder than before the CO2 doubling is valid;

An AGW thought experiment is proposed to investigate the climate effect of doubling atmospheric CO2 in a century:

It must be a thought experiment which isolates the change in CO2 and holds all energy inputs constant since we cannot control for all of the unknown variables which confound our attempts at verification measurements and attributing measured temperature changes such as:

"The problem with AGW is that climate models have to deal with many more variables than weather models. They have to model all of the variables that weather models contain including for instance Solar activity including cosmic ray cloud effects, orbital effects and minor changes in radiation intensity, plus: (for instance)

• Land biology

• Sea biology

• Ocean currents

• Ground freezing and thawing

• Changes in sea ice extent and area

• Aerosol changes

• Changes in solar intensity

• Average volcanic effects

• Snow accumulation, area, melt, and sublimation

• Effect of melt water pooling on ice

• Freezing and thawing of lakes

• Changes in oceanic salinity

• Changes in ice cap and glacier thickness and extent

• Changes in atmospheric trace gases

• Variations in soil moisture

• Alterations in land use/land cover

• Interactions between all of the above

• Mechanisms which tend to maximise the sum of work and entropy according to the Constructal Law."

However we can devise a simple thought experiment which holds all other ill-defined as well as unknown energy modulation variables constant to evaluate the effect of the CO2 input variable on an otherwise constant earth energy climate model.

CO2 Greenhouse:

In this reference the IPCC Figure SPM5.1 as well as others published by the IPCC AR-5 WG-1 attributes a reduction of 1.85 watts/m2 IR radiation to space due to a doubling of the CO2 blanket thickness at the top of the troposphere. Although there may be reasonable arguments about where exactly in altitude and temperature lapse rate curve some or all of the CO2 spectrum is effectively radiating, assume for purposes of this discussion that 100% of this conjecture is true . It therefore represents the maximum CO2 "greenhouse" quoted from the latest effect calculated by NASA .

A Constant input Power Model:

How does the climate respond to the conjecture of this blanket effect of CO2 doubling at the top of the troposphere where it will radiate 1.85 watts/m2 less IR to space from the edges of the 15 u band? Obviously the earth must heat up to provide a temperature increase in the water vapor to increase its radiation by this amount to drive the earth energy toward a steady state average balance. While the driving force is the increase in CO2 of 1%/year, the earth will always respond to catch up with a required atmospheric temperature increase, otherwise the earth's mass temperature would continue to rise without any compensating energy balance in radiation to space. A warming scenario based on the steady state solution is described here.

The earth has dealt with much larger transient inputs to the system including changes in power input and has managed to provide the earth with incredible climate stability (particularly upper average temperature) for hundreds of thousands of years.

Paradigm shift: To isolate the CO2 GH effect from all other variables, remembering the Law of Conservation of Energy, in this scenario nature has no additional or reduced energy to work with and thus will continue with the hydrologic solution which has evolved over the millennia to balance the constant solar power by shifting the missing CO2 GH radiation over to a compensating increase in water vapor radiation.

Model approach:

Since CO2 increase adds no additional energy to the system:

Our challenge is to understand how the climate will adjust to the absolute energy balance requirement. Calculating changes in conduction, convection and radiation in the random chaotic atmosphere have proven to be more challenging than we can ever hope to address with our limited computing power not to mention limited understanding of the detailed spatial and temporal physics of cloud formation in the hydrologic cycle. Perhaps the correct approach is to let the natural system recalculate and rebalance as it has done for millennia and observe the result.

As the CO2 accumulates blocking the calculated reduction in IR spectrum ~20 milliwatts/m2 each year over the coming century, the earth will accumulate this energy raising its surface temperature and the surface strata atmosphere temperature by dT/year . Thus the atmospheric water vapor will increase its radiation an average 20 milliwatts/m2 each year to the some 220 watts/m2 which it is already radiating to space along with some 20 watt/m2 through the "IR window".

Since in this experiment the solar input to the earth including cloud effects, volcanos and all other energy inputs (some of which are listed in the introduction) to the earth are held constant to allow us to concentrate on the effect of CO2 'forcing' alone, the energy flux into the earth and from the surface to the atmosphere is thus constant. This requires that the average surface/atmosphere temperature gradient is constant and unchanged as required by a constant energy flux albeit at an increasing temperature of both surface and atmosphere of dT/year. Most of this energy transfer remains the constant evaporation rate of water containing its latent heat of vaporization. The surface radiation which remains constant through the constant surface/atmospheric strata temperature gradient continues to be captured at the same constant rate and immediately thermalized by the GH gasses. The atmosphere temperature lapse rate curve moves 'to the right ' by dT each year along with the surface temperature increase so that by the end of the century it will be displaced by 100dT higher temperature thus the constant water vapor pressure will radiate an additional ~1.85 watts/m2 to space.

Climate physics:

Since the lapse rate is constant, the cloud behavior, constant water content, vertical temperature profile, energy release and conformation need not change and indeed will have no additional energy(water vapor) input to do so. Since its condensation level is a function of temperature, clouds will start at an average altitude increasing by dz=dT/6.5C/km each year so that by the end of the century the clouds need not change in form, size. extent, temperature or temperature gradient but be 100dz=100dT/6.5C/km higher occupying exactly the same temperature gradient as before the 100 dT shift in atmospheric temperature started. Since the clouds have no change in energy or in temperature gradient they will radiate IR in exactly the same fashion but into an atmosphere which has a reduced water vapor pressure(increased altitude) and so radiate upward more efficiently. The clear atmosphere water vapor will have exactly the same water vapor pressure gradient as before but each year will radiate at a temperature dT higher throughout all altitudes. In other words nothing need be changed except the altitude of the clouds which have exactly the same temperature profile and conformation as before except at an increased altitude dz. We see that the natural atmosphere solution (that we have described as random chaotic) which nature has developed over the millennia to maintain energy balance will require no change except that cloud height will rise by dz each year to maintain their vertical temperature profile and that clear air fixed water vapor pressure will be radiating at an increased temperature, dT each year.

For illustration; some calculation of the average energy flow and temperature changes of a one dimensional average temperature and radiation model is shown.

A very minor energy balance adjustment;

Since the surface temperature will increase by 100dT by the end of the century, the radiation through the IR window will increase thus requiring slightly less (~1%) water vapor energy radiation thus reducing the overall atmospheric temperature increase requirement to slightly less than that described below.

Temperature increase;

Raising a 255K black body(which seems to be favored by NASA) by 100dT= .5K will increase the radiation to space calculated from the Stephen-Boltzmann radiation equation by 1.886 watt/m2 which will suffice to balance the CO2 IR spectral reduction due to the CO2 blanket at the end of the century .

Thus the 20 milliwatts/m2 yearly increase in water vapor radiation will require an increase of dT=5 millideg C/year * for a century to balance the CO2 blanket accumulation over the century. (* Yes, we know that dT is a 4th root function of power but at these small increments to the base temperature of 255K it is within ~5% of linear and matters little in understanding the big picture)

Change in nominal cloud base (and top) altitude is; dz=.005/6.5 = .77 m/year or 100dz= 77 m/century.

To state the obvious, the earth need not employ any new different or complex physics (indeed, considering CO2 increase alone) there is no increase or change in energy flux (vaporization rate) available to power any change). The earth and atmosphere temperature will increase by the required 0.5K over the century to shift the required 1.85 watts/m2 missing from the CO2 blanket to the water vapor radiation budget.

Stating the law of conservation of energy in this context:

Again stating the obvious; (although the back radiation/positive water vapor feedback is disproven physics) for those who choose to retain this paradigm in their thinking, there is no additional energy flow (constant gradient) therefore no additional water vaporization and thus whatever the present day situation re. water vaporization/radiation is, there can be no change, whatever one might believe re. water vapor/radiation feedback there is no additional power to drive an increase in such a 'loop'.

Any tendency to raise the surface strata temperature above(below) normal would reduce (increase) the temperature gradient thus limit any change in energy flow(most importantly WV). With a constant energy flow available this is a self-limiting and unchanged constant average surface strata gradient at the new nominal steady state average earth surface and atmospheric temperature of 288 +.5 K. (15.5C) and average atmospheric radiation temperature of 255+.5K.

If any of you remain inspired for whatever reason to continue with your avocation to study the random chaotic climate physics, all I can say is join the rest of the fleas on this elephant's hind leg and keep your eye on the prize, everyone needs a goal in life.

Can you provide a link for this study? I'd like to know where this was publushed.