On Evaporation, the Scientific Battle Rages

Since they lose pretty much every argument, the global warming fraudsters try to tell us that the science is settled, and we should all just shut up. In fact, however, debates over various aspects of climate science are constantly raging. This one is a great example: “Major Errors Apparent in Climate Model Evaporation Estimates.”

But first, let’s set the stage. It is generally accepted that ceteris paribus, increasing the concentration of CO2 in the atmosphere will tend to increase global temperatures, slightly. The problem–from the warmists’ standpoint–is that the increase is trivial, 1 degree C tops. So the only way the alarmists can create frightening scenarios is by hypothesizing positive feedback effects that will increase that one degree to six or seven. It is easy to devise a model that incorporates extravagant feedback assumptions, and therefore will kick out scary predictions. Fantasy in, fantasy out.

In fact, there is a vigorous debate about feedbacks: What are they? Are they positive or negative? If positive (or negative), what is their magnitude? Science does not yet give us the answers to these questions. So the debate goes on. This analysis suggests that the alarmists’ models have failed to deal properly with evaporation, and that may account for the fact that they have proved to be wildly inaccurate. It is instructive to read the entire post, and then the comments. Having done so, contemplate the liberals’ hysterical insistence that the debate is over. In fact, as any rational observer can see, the debate has barely begun:

The physics of evaporation has complications related to what happens at the water / air interface such as wind speed and wave action. However if these factors remain constant, how evaporation changes with temperature and humidity can be estimated with well-known equations based on how water vapor pressure varies with temperature. For example, at a typical ocean temperature of 17 C, it should increase about 6.5% / C if the water vapor increases to maintain relative humidity, that the climate models indicate. If the surface air tracks the water within ± 2 C, the rate varies from 6.2% to 6.9% / C. Data over oceans by Wentz et, al (2007) report values of about 6% / C.

But the complex computer climate models show averages of only about 2.5% / C. There are no claims of reduced wind speeds or wave action or increased relative humidity to explain this. However many papers on the subject claim that the available energy is limiting evaporation in these models. But physics theory tells us that the latent energy for evaporation comes from the temperature of the water itself. The latent heat leaving the surface cools it and deposits heat in the atmosphere, part of which escapes to outer space. This combination causes negative feedback. The reduced net energy from increased CO2 still warms the surface, but this energy can’t be separated from what aids the final increased evaporation. A 6% / C increase applies to the water after the negative feedback is complete. Do the climate models ignore this cooling and feedback process? …

[T]he developers of the climate models seem to be confusing independent and dependent variables. Evaporation is the driver or forcing agent controlled by the physics at the surface, and G and D must respond to a change in it. If the surface temperature rises, the additional latent heat lost at the surface will cause an offsetting decrease in the temperature and thus G. And the latent heat deposited in the atmosphere warms it and increases the downwelling radiation, D (and the outgoing radiation). We now have a feedback process at work. Equation (1) can only be used as a check after a correct solution is found to new values of E, D and G after the feedback process is complete. It appears there is a serious error in how climate models estimate evaporation as indicated in the rest of this paper.

We have developed a dynamic three level energy balance model (reference 1) with updates as described later that can be used for a number of forcings and feedbacks including the response to changes in evaporation and the cooling of the surface and the warming of the atmosphere.

The results are shown on the next page. No energy constraints of evaporations are seen. …

It appears the climate models are grossly underestimating the negative feedback from latent heat transfer. For case 3 in the table above, the feedback multiplier of 1.57 / 2.70 = 0.581 implies a feedback factor for a change in evaporation of 6% / C of –0.720 C / C. This corresponds to the IPCC value for water vapor of 1.8 Wm-2 / C divided by their value of l of 3.2 to give a feedback factor of +0.562 C / C. …

The IPCC has a positive cloud feedback of 0.69 Wm-2 / C with a very large range. But it is not based on reduced clouds with warming, but as a residual of the amount of warming the models can not explain by the other feedbacks (Soden and Held (2006), p 3357, paragraph 2). So this is not a true estimate of cloud feedback. Eliminating it and replacing the lapse rate feedback with our evaporation feedback cuts the IPCC feedback multiplier from 2.48 down to 0.910.

There is much, much more, replete with equations and calculations. Is this analysis correct? I am not competent to judge, but it is obvious even to the casual observer that all of the real climate science is currently being done by the realists, not the alarmists. Far from being complete, our understanding of the Earth’s climate is in its infancy. The last thing we should do at this point is be guided by politically-motivated charlatans who try to shut down the process of scientific inquiry.


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