RealClimate: Unforced Variations: Jun 2023

Replying to

macias shurly

https://www.realclimate.org/index.php/archives/2023/06/unforced-variations-jun-2023/#comment-812311 ,

Piotr

https://www.realclimate.org/index.php/archives/2023/06/unforced-variations-jun-2023/#comment-812262

and

https://www.realclimate.org/index.php/archives/2023/06/unforced-variations-jun-2023/#comment-812255 ,

JCM

https://www.realclimate.org/index.php/archives/2023/06/unforced-variations-jun-2023/#comment-812293

and also to Barton Paul Levenson

https://www.realclimate.org/index.php/archives/2023/06/unforced-variations-jun-2023/#comment-812237

and

https://www.realclimate.org/index.php/archives/2023/06/unforced-variations-jun-2023/#comment-812238 ,

nigelj

https://www.realclimate.org/index.php/archives/2023/06/unforced-variations-jun-2023/#comment-812223

and

https://www.realclimate.org/index.php/archives/2023/06/unforced-variations-jun-2023/#comment-812294 ,

Kevin McKinney

https://www.realclimate.org/index.php/archives/2023/06/unforced-variations-jun-2023/#comment-812254 ,

Ron R.

https://www.realclimate.org/index.php/archives/2023/06/unforced-variations-jun-2023/#comment-812281

and Carbomontanus

https://www.realclimate.org/index.php/archives/2023/06/unforced-variations-jun-2023/#comment-812284

plus

https://www.realclimate.org/index.php/archives/2023/06/unforced-variations-jun-2023/#comment-812305 .

Dear colleagues,

1) First of all, I am not sure that the present discourse about the article Schmidt et al. https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2010JD014287 and the “cooling” or “warming” effect of water cycle based on this article does make sense.

In my understanding, the article simply takes the difference in black body radiation flow 155 W/m2 that corresponds according to Stefan-Boltzmann law to observed difference 33 K between the observed mean surface temperature of Earth (15 °C) and calculated mean surface temperature without atmosphere (- 18 °C), and strives to formally distribute this value between various “greenhouse agents”.

Please note that in this approach, all non-radiative energy flows (approximately 100 W/m2, if we count both latent as well as the sensible heat) are already included among these “greenhouse agents”.

I suppose that the observed value characterizing the greenhouse effect would have been, actually, significantly higher than observed 33 K if there were no non-radiative heat fluxes at all. Thus, the non-radiative flows are already subtracted from the actual greenhouse effect. In other words, Gavin et all simplify the real situation by assuming that there is radiative energy transfer ONLY, and then formally ascribe the observed temperature difference to real “greenhouse agents”.

I am afraid that this approach cannot bring the sought clue to the question if an isothermal increase in water cycle intensity will cool the Earth as assumed by me, macias and JCM, or warm it, as assumed by our opponents.

2) As regards the relationship between water cycle and the latent heat flow in Trenberth’s diagrams for global energy budget, I still think that Piotr may be mislead.

If we take mean annual precipitation 990 mm

https://en.wikipedia.org/wiki/Earth_rainfall_climatology

and consider that evaporation of 12.5 mm water column requires annual heat flow 1 W/m2, we get latent heat flow 79 W/m2 fitting well with published diagrams. Herein, I should correct myself – the 130 000 km3 mentioned by macias is certainly not the volume of global annual precipitation, because for 990 mm, the annual global precipitation will amount ca 504 000 000 km3. I think that the 130 000 km3 was rather the amount of annual precipitation on the land that does fit with macias’ data, wherein the latent heat flux is 86 W/m2.

Irrespective of uncertainties in the values of the global rainfall, I think these are one of a few relatively fixed points that may help us to progress further in the present debate. I think so because all the water that fell down from the sky
– had to evaporate previously and
– would have not condensed if it had not lost its latent heat.

I have not tried to calculate how much the condensation of 500 000 000 km3 water would have heated the atmosphere if the released heat were not radiated out in the space. I think it is basically unnecessary, because if the latent heat comprised in the vapour could not be released, all this water vapour would have never condensed nor precipitated and would have actually stayed in the atmosphere instead.

I therefore suppose that Piotr’s objection (that we should consider the back-radiation of a significant part of the condensation heat towards the Earth surface) is in fact unsubstantiated, and that all this ping-pong between upwelling and downwelling radiation is already more-less correctly included in diagrams showing the “energy budget”.

3) As regards Claudius Clapeyron equation

I admit that although I am physical chemist by education, I have never studied non-equilibrium thermodynamics and do not know if the validity of this equation can be somehow extended to non-equilibrium systems, as supposed by Carbomontanus. Honestly, I rather tend to agree with macias who assumes that from the viewpoint of classical thermodynamics, the Earth is a non-equilibrium system, and that extending laws derived for the equilibrium systems to the entire Earth may be tricky.

4) To the exchange between macias and Barton Paul

BPL: “you post things like less water vapor in the atmosphere causing a temperature increase”

I think that Barton Paul misinterpreted what macias strived to communicate, due to an incorrect assumption that water content in the atmosphere must be commensurate to evaporation intensity. There is, however, no such simple relationship, because water condenses and precipitates. As macias mentioned, global annual evaporation (and precipitation) is about 500 000 000 km3, whereas the mean water amount in form of atmospheric vapour is about 13 000 km3 only.

I do not think there is a principal rule preventing the Earth from changing the global annual precipitation value of 500 000 000 km3; it is in my opinion just the present value. Of course it may change with changing mean surface temperature, but I strived to show that it can change also in an isothermal regime.

In other words, even when the surface temperature stays constant, you can change these 500 000 000 km3 of annual precipitation significantly, if you will turn Earths 13000 km3 of atmospheric vapour around more quickly or more slowly.

5) Remark regarding geoengineering

Production of non-condensing greenhouse gases is no way the sole geoengineering experiment the humankind is running. In the industrial era, we can mention e.g. production of sulfate aerosols or production of compounds depleting the ozone layer.

The longest human geoengineering experiment is, however, introduction of agriculture, urbanization and huge changes in Earth water regime related thereto. I think that the efforts exhibited by macias and JCM who tirelessly strive to show the importance of this fact deserve not only attention but also respect.

I would like to add that neither macias, nor JCM, nor me proposed to deal with water cycle repair INSTEAD of mitigation of the greenhouse effect, as incorrectly assumed by Piotr

https://www.realclimate.org/index.php/archives/2023/06/unforced-variations-jun-2023/#comment-812308 .

6) A personal remark

I am aware that even merely asking publicly relevant questions can be harmful or even deadly in certain extreme situations. An example can be e.g. disclosure of secrets important for defence or other vital interests of the democratic society, but I believe that there is no such threat in the present discussion.

I think that the only prevention against serving as a useful idiot is a good understanding to what is actually going on. In this sense, I thereforre think that asking questions, wherever one sees or feels discrepancies in the publicly accepted picture, may be helpful.

I believe that if my questions are mislead, the faults can be explained and corrected. I do not see any particular harm that might arise from such procedure, rather oppositely. I think that our debate already showed that some seemingly clear things are in fact more complex and hope that a further thorough discussion may improve my understanding further.

6) Thank you all for your contributions!

Greetings

Tom