RealClimate: Unforced Variations: Aug 2023 – GWC Mag

In Re to

https://www.realclimate.org/index.php/archives/2023/08/unforced-variations-aug-2023/#comment-813793 ,

Area-based global hydro-climatological indicators

and

https://www.realclimate.org/index.php/archives/2023/07/area-based-global-hydro-climatological-indicators/#comment-813773 .

Dear Carbomontanus,

I apologize for not examining your references to WUWT and other similar sources – it is just for limited time and energy I have, not for lack of respect to you.

Let me touch a few specific points from your posts that puzzle me.

1) Earth surface cooling by latent heat flow, rain recycling, biotic pump hypothesis

These topics are interrelated, however, each of them has in my opinion a significantly different position in present picture of Earth climate as regards the level of certainty / scientific understanding.

a) Earth surface cooling by latent heat flow

I highly appreciate recent remark

Area-based global hydro-climatological indicators

by Barton Paul Levenson, reassuring me that it is indeed a standard part of state-of-art climate science and that my source of this knowledge (the textbook Physical climatology written by prof. Dennis Hartmann, to that I several times referred during the previous discussion) is trustworthy and reliable.

b) Rain recycling by terrestrial vegetation

I have not checked in detail how strong is the evidence for so called rain recycling (mechanism of a stepwise moisture transport from the ocean to interior of continents, enabled by re-evaporation of moisture precipitated on land, wherein it is supposed that evapotranspiration by plants significantly contributes thereto). There are publications supporting the existence of this phenomenon by analyses of stable isotope ratio in rainfall, and I hope that the respective measurements were made carefully and rigorously and that the obtained data were evaluated and interpreted cautiously. As a summary of this point, I presently do not see reasons for doubting that the rain recycling by water re-evaporation from land indeed works and that the terrestrial vegetation indeed does play an important role therein.

c) “biotic pump” hypothesis

Different from rain recycling, I still see the “biotic pump” hypothesis (assuming that large land areas with an intense “small” (local) water cycle may enhance water transport from the ocean into this area, establishing this way a stable steady state that may exhibit a strengthened resilience against external disruptions such as e.g. changes in global mean temperature, oceanic currents etc.) as an appealing idea that has neither a strong theoretical background, nor a solid observational support yet. On the other hand, I do not see any strong theoretical reason or observational evidence disproving this hypothesis. Therefore, I still think that it may deserve a serious attention from the mainstream climate science.

I am afraid that I still do not understand what is actually your view on these topics.

2) Greening vs drying of continents and paleoclimate evidence as a support for hydrological regime predictions in the present climate change

It appears that present climate models predict a slight increase in the total annual global rainfall with rising global temperature and that this prediction is in accord with a global trend observed during the last decades.

Nevertheless, the works published / cited by rasmus do not appear to mention any general trend to more rainfall on the land, and they rather seem to disprove claims like “Sahel is greening”. On the other hand, I have not seen yet any data convincingly supporting hypotheses about a general trend to “continental drying”. This is the reason why I asked explicitly if the available data show a general trend in higher water transport from ocean to continents, and what is regional distribution in observed development in hydrological cycle intensity.

I am not sure that a shift of present Earth climate to an analogue of Pliocene warm wet climate in central Europe may necessarily be a pattern followed by present climate change. I think that there are at least two reasons for a high uncertainty of such assumptions. First, I think that positions of continents and oceanic currents may have changed since Pliocene; second, at the very start of Pliocene, there was quite likely no equivalent of the present human interference with climate-relevant aspects such as terrestrial vegetation cover.

3) Recommendations of a holistic approach vs requirement for a monocausal explanation of observed phenomena

It appears that you, on one hand, often mention a holistic approach that should help understanding the Nature, on the other hand, I have rather a feeling that you assume that the observed climate change must have a single cause. I think so because you assign the people discussing possible complexity of the mechanism of the present climate change as “denialists”, striving to disprove the role of radiative greenhouse effect in climate regulation.

Personally, I have rather a feeling that “monocausal” phenomena are rather rare in the Nature, and that identification anthropogenic greenhouse gas emissions as a “suspect” in the observed climate change does not exclude that this suspect may have an accomplice (or more accomplices).

Greetings

Tomáš