By Charles T Blaisdell PhD ChE
Abstract
In addition to WUWT, more and more web sites are mentioning cloud reduction as a source of climate change, but offer no source of the cloud reduction. WUWT was the first to published this author’s theory: Cloud Reduction Global Warming, CRGW, (1). A critical part of CRGW theory is the relationship between Vapor Pressure Deficet, VPD, and Cloud Fraction. The relationship is logical: as the atmosphere’s water vapor concentration approaches the due point the probability of cloud formation should increase.
Previous papers by this author have shown that Vapor Pressure Deficit and cloud fraction are loosely correlated (low R^2). The measurement of cloud fraction seems to be the main uncertainty. This essay will show that downwelling Short Wave, SW, radiation to the earth’s surface along with atmospheric enthalpy, En, correlate to Cloud Fraction, CF, thus increasing confidence in VPD as a predictor of cloud fraction. VPD and En are necessary variables in the Cloud Reduction Global Warming , CRGW, model which models current climate change using Clausius–Clapeyron related equations.
Slicing the earth’s data reveals the change in atmospheric VPD and En vs latitude correlate to cloud fraction. The earth’s slices suggestion that lower land cover in a slice may be related to cloud cover in addition to the expected sun angle.
But, CO2 and VPD are confounded. Which one is guilty of climate change?
Introduction and background
The CRGW theory is simply put as: Less water evaporating from land into the atmosphere results in less clouds (less clouds, more sun). Previous attempts to extract VPD vs cloud fraction correlation vs month were unsuccessful due to the more powerful inter hemisphere forces. Annual data does not have the inter hemispherical variability.
The annual data was sliced into 8 slices by latitude to obtain data of the temperature (Temp), specific humidity (SH), and cloud fraction (from NASA’s Physical Science Laboratory, (4) and Climate Explorer, (3)). Temp and SH are the only variables needed to calculate VPD and En. En is a variable that measures the heat (potential energy) present in the atmospheric air at the altitude the Temp and SH data was taken. En is the atmosphere’s part of the earth’s energy budget (Changes in En are part of the Earth’s Energy Imbalance, EEI).
The equations used for calculating VPD and En are:
Water saturation pressure, Pws, is from Vaisala Oyj (2013), (2):
| Pws = 6.116441*10^((Temp * 7.591386/(240.7263+Temp))) | (in hPa) | Eq 1 |
(Note: the above is not an Arrhenius equation but give similar results.)
Water vapor, Pw, pressure is from Vaisala Oyj (2013) (2):
| Pw = SH *1000/(621.9907+SH) | (in hPa) | Eq 2 |
| VPD = Pws – Pw | (in hPa) | Eq 3 |
Enthalpy, En, Vaisala Oyj (2013) (2):
| En = Temp * (1.006+0.00189*SH)+2.501*SH | (in kJ/kg (da) ) | Eq 4 |
These equations are not in Clausius–Clapeyron format but simplified for more convenient use with water.
A clarification of the annual data used. The VPD or En data is not derived from one point but is the average of many data point over many months. Thus a VPD of say 4.0 hPa (which is nowhere near the dew point) is the average of a wide range of points from about 10 to 0 hPa. Only the points near 0 could have clouds. Cloud fraction includes rain clouds, high and low clouds, and partly cloudy. The more data that goes into a temperature or specific humidity annual number the higher the probability of an accurate prediction of cloud fraction.
New Cloud Fraction data
New Cloud Fraction, CF, data was found at Climate Explorer (3) , Figure 1. The big decrease (from previous) in average cloud fraction is very noticeable. The decreasing slope is a little less than the old data (downloaded in 2021). The new CF data has a better R^2 and both old and new data seemed to suggest no decrease in CF after 2003. The new data shows Mt Pinatubo eruption (1991 to 1994) better than the old data.
With decreasing CF one would expect that shortwave, SW, radiation to the earth’s surface would be increasing. Likewise, the VPD and the En should be increasing. Figure 2 suggests that all three (SW radiation, VPD, and En) do. Figure 2’s 2003 to 2021 data suggest an increasing slope for these three variables when the CF chart suggests a flat response. This observation could be interpreted as a lack of sensitivity to the CF data or there is another source of energy to the atmosphere. Since atmospheric SW radiation can only come from the sun the lack of sensitivity in the CF data is the most probable explanation. If this is true SW radiation to the surface may be a proxy for CF.
A check on incoming SW radiation variations, Figure 3, suggests that some of the perturbations in the sun’s irradiance line up with the SW radiation perturbations to the surface, but the magnitude of the perturbations is small compared to the overall increase in SW radiation to the surface. Figure 3 uses the same scale difference in SW radiation as the SW to the surface graph (to be accurate the difference use for the solar irradiance should be ¼ of that shown (to allow for day/night and the curvature of the earth) making the solar perturbations even less significant.
Slicing the Earth
The earth was sliced in 20 deg sections shown in Figure 4. The expected temperature profile shows a small shift in temperature from the 1970 period to the 2020 period with the maximum change in temperature occurring either side of the angle the sun is hitting, no surprise.
Figures 6 and 7 investigate Cloud Fraction correlation to VPD and En (using equations above).
The CRGW model for predicting climate change relies on a good correlation of VPD to Cloud Fraction and Enthalpy. Figures 6 and 7 show that the looked for correlation is present in the earth’s slice data as well as the correlations used in the model. Figure 6 has an interesting point that does not seem to belong (circled in red) that is the only data point that has no land in it’s slice. With that curiosity Figure 8 was plotted showing that the amount of land in a slice correlates to the percent of the temperature change in that slice. This is the expected correlation for the CRGW theory: since the change in ET originates from land it should correlate to land area.
Figure 9 shows the expected correlation of sun angle to temperature change. Note correlation to Land is stronger than to sun angle.
What about CO2?
To be fair, an attempt was made to plot CO2 data for these graphs, all that was found were NASA pictures. Interpreting the pictures, it was obvious that for CO2:
- Annual CO2 concentration is lower in the southern hemisphere, annual VPD is lower.
- Annual CO2 is higher over land, annual VPD is also higher.
- Annual CO2 is increasing over time so is annual VPD
Is VPD following CO2 or the other way around?
It should be unquestionable that decreasing clouds result in increasing downwelling SW radiation to the earth’s surface. The CRGW theory shows how VPD is increased by decreasing evapotranspiration, ET, on land which in turn decreases Clouds. How does CO2 decrease clouds?
The IPCC is working on models, (5) that use Radiative Forcing’s, RF’s, theorized heat generated in the upper atmosphere to reduce clouds – no published explanation of cloud reduction.
Discussion
The earth’s data in slices from 1970 to 2024 reinforces the correlations used in the CRGW model.
Surface SW radiation increasing with time along with VPD and En adds to the confidence that Cloud Fraction or thinning is changing as VPD changes.
CO2 and VPD are confounded. To understand and manage climate change science needs to find out which one is in charge. Man knew about CO2 and its greenhouse properties before cloud reduction was observed and the VPD and ET relationship in the CRGW theory was proposed. Therefore, it is understandable that CO2 theory occupies the bulk of climate change scientific discussion. To be fair to the “scientific method” alternate theories should be scientifically discussed to allow a theory to rise to the top or die of their own lack of scientific weight. When is it CRGW’s turn
Bibliography
- “Cloud Reduction Global Warming, CRGW 101. A Competitive Theory to CO2 Related Global Warming” (2025), by Charles Blaisdell, web link Cloud Reduction Global Warming, CRGW 101. A Competitive Theory to CO2 Related Global Warming – Watts Up With That?
- “HUMIDITY CONVERSION FORMULAS” by Vaisala Oyj (2013) web link Humidity_Conversion_Formulas_B210973EN-F (hatchability.com)
- Climate Explorer web site Climate Explorer: Select a monthly field (knmi.nl) .
- Physical Science Laboratory Monthly Mean Timeseries: NOAA Physical Sciences Laboratory
- CMIP6: the next generation of climate models explained by Zeke Hausfather web link CMIP6: the next generation of climate models explained – Carbon Brief
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Neither is in charge.
Convection changes as necessary to neutralise any net thermal effect from either.
The temperature for a surface beneath an atmosphere within a gravitational field is set only by atmospheric mass and the power of insolation.
Changes in atmospheric gases only influence the pattern and speed of convection.
such change from an increase in CO2 would be negligible since it is merely a trace gas.
Erl Happ has many essays on the topic of movement of mass about 14yrs ago on WUWT and his own site and has definitively shown CO2 does not drive climate and radiative theory poorly describes temperature.
https://reality348.wordpress.com/
Here’s NASA video images from 2006. Weird the narrator says how well manmade emissions mixes, yet the video shows nothing crossing the equator.
https://youtu.be/x1SgmFa0r04?si=BypQTTcHVOZbM8ag
Nice one. But the link to the download w all the details does not work..
Which link? Both work fine for me. Not have a wordpress account maybe?
Careful Stephen, you are treading on the still contested ground of “What is the temperature profile of a column of gas in a gravitational field ?” that has caused much controversy both here in WUWT posts in the past…not to mention Boltzmann, Maxwell, and Loschmidt long ago…
“Who is in change” Just trying to add some humor. More technically correct which variable moved or was moved first to cause cloud reduction, VPD or CO2. Then what moved VPD or CO2 etc..
To understand and manage climate change science needs to find out which one is in charge.
Neither. “Climate science” is an oxymoron, since climate is just the statistics of weather observations.
If you accept that the surface was once molten, and is not now, then considerable cooling has taken place – to the present state.
It’s a matter of observation, supported by experiment, that reducing the amount of solar radiation reaching a thermometer results in the thermometer cooling. Clouds passing between the Sun and a thermometer have this effect.
This phenomenon has been noticed for millenia. Increased CO2 in the atmosphere also reduces the amount of solar radiation reaching the surface, as does H2O gas. Tyndall noted this over 150 years ago – amongst many other things which so-called “climate scientists” still refuse to believe.
After reading about CO2 for the umpteenth time since 1984, when I first started studying about it to help with my new assignment in business development and marketing for enhanced oil recovery (IOC); I continue to be amazed at all the ta-do about ATM CO2. It seems odd that it’s wonderful at 280 PPM but an existential catastrophic climate catastrophe at 560 PPM. I can’t shake the idea that 0.000280 can’t be that different from 0.000560.
Carbon dioxide (CO2) at 4000 parts per million (PPM) can cause symptoms like headaches, drowsiness, and poor air quality. However, it is not immediately suffocating at this level. CO2 becomes dangerous at much higher concentrations, such as 40,000 PPM (4%), where it is considered immediately life-threatening.
That may well be the effect on a human living in a 400ppm world. Someone brought up in a 3950ppm environment might have a different reaction to an additional 50.
I’m don’t know why this got a down-vote without an explanation. It should be obvious that those born and raised in the Himalayas and the Andes have adapted to low levels of oxygen. Humans are remarkably adaptable. Why would one not expect some level of adaptation to high levels of CO2 if exposed from birth? Stomata in plants clearly adapt.
4000 ppmv does not cause issues such as headaches, drowsiness or poor air quality, according to the US Navy, where submarines typically have atmospheres around 4,000 ppm of CO2, and up to 10,000 ppm is not considered a problem. As you can imagine, the Navy has a lot of experience with this, and the typical 3-8,000 range is pretty much considered “normal”. Perhaps there are some people out there who “can” experience such effects, but that would probably represent some other medical issue. Much higher levels, 20,000 can cause problems, and 40,000 is dangerous.
“We try to keep CO2 levels in our U.S. Navy submarines no higher than 8,000 parts per million, about 20 time current atmospheric levels. Few adverse effects are observed at even higher levels. – Senate testimony of Dr. William Happer”
and – “Data collected on nine nuclear-powered ballistic missile submarines indicate an average CO2 concentration of 3,500 ppm with a range of 0-10,600 ppm, and data collected on 10 nuclear-powered attack submarines indicate an average CO2 concentration of 4,100 ppm with a range of 300-11,300 ppm.” (Hagar 2003)
OMG! At 4000ppm, those poor squids are being sous vide!
BobM: On submarines, the crew consists mostly of young, physically fit, and well-conditioned individuals who undergo rigorous training and acclimatization to operate in controlled environments. This demographic is far from representative of the general population, making their ability to tolerate higher CO2 levels an imperfect comparison. If the crew consisted entirely of marathon-level athletes, the example would diverge even further from everyday scenarios. General populations face exposure to CO2 in uncontrolled settings, often with the added challenges of dust, pollen, and other airborne particulates.
Well, perhaps. Young and physically fit, sure. My brother served in a nuclear-powered attack sub in his mid-20’s and was not really much more physically fit than I was, working at a large Corporate Data Center. He is 2 years younger, graduated through Navy ROTC with a 5 year commitment, and had multiple multi-month undersea trips as a young officer. But when back in port and home again visiting, I wouldn’t say he was much different from any young healthy person. They knew the sub’s atmosphere was likely 20 times “normal”, but couldn’t tell the difference. Of course it was monitored and he said they only cared if it got above about 13,000, if I remember correctly, and that would square with some of the studies I’ve seen.
The other challenges imposed by dust, pollen, etc., are separate issues from sensitivity to “high” levels of CO2. There are always sick or unwell people that can be found suffering from something. Just ask the EPA.
P.S. – The Captain of the boat and some senior officers were not nearly as “young”… 30’s, and the Captain 40-50-ish, again, if I remember correctly.
“NASA has set the maximum allowable 24-hour average CO2 on board the ISS at 5 250 ppm (4.0 mmHg).”
During the Apollo 13 mission, it got up to 19,600 in the capsule.
In table format. Just climb a 150m hillside and you’ll likely experience the claimed CO2 effect on temperature. No crisis.
Whoever downvoted you is an idiot or has fat, imprecise fingers. You just posted facts, that showed higher CO2 levels are not a health risk even a several multiples of the current level – as if the green mob care 1 iota about human well-being. At least they should appreciate all the plant growth benefits of 1500ppm of CO2.
The planet is not likely to cross 600ppm by the end of the century but it’s better than the status quo.
Quite astute D Sandberg. The very best line-by-line analyses show that the doubling of CO2 results in 3 watts per square meter additional sunlight absorption at surface. That’s about the wattage of the average laptop computer cooling fan. Now consider how much turbulence that 3 watt fan could induce in a column of atmosphere 1 meter square by 10 Km tall (the amount 10 tonnes being that which exerts atmospheric pressure on the surface).
Yes, you are correct….FN zero.
Frightfully near zero.
Well, the analyses don’t agree with experiment. Additional CO2 in the atmosphere results in less solar radiation reaching the surface, depressing daytime maxima, not any increase surface absorption of sunlight.
Supported by John Tyndall’s experiments going back 150 years, and supported by subsequent experiments. Your “very best line-by-line analyses” are garbage if they disagree with experiment.
Sorry about that.
CO2 does not absorb sun light (downwelling SW radiation) it absorbs out going LW radiation in about 3 frequencies. the absorption is described by the Beer-Lambert Law. At 300ppm CO2 99% of the radiation that can be absorbed is absorbed with in 40 ft of the earth’s surface. More CO2 will not change the absorption very much.
Yes, it does. 50% of the solar energy is near IR and CO2 has absorption bands in that range.
Climate science never seems to include this in any radiative process discussion. Just one more garbage assumption by climate science.
EOR not IOC. I’m the same age as Biden, and it’s starting to show.
Since you wrote it out just before you introduced the acronym it was pretty clear to all of us methinks.
560ppm is just a good initial target – the biosphere would prefer something like 1500-2000ppm to maximize plant growth and minimize water loss.
We should really strive for greenhouse levels of the world’s ‘greenhouse’ gases!
What about CO2?
Well, we cannot really do without it. I think it’s time that they stopped looking at the Earth as a sealed bubble and recognised off world influences…
Cosmic Lightning Strikes Earth: The Wildest Energy Levels Ever Seen https://nasaspacenews.com/2025/01/cosmic-lightning-strikes-earth-the-wildest-energy-levels-ever-seen/
I’m leaning towards a theory that CO2 and water vapour doesn’t cross the equator (or very little) due to the correolis effect. Even tropical cyclones don’t cross. So with NH having 90% population and 70% of land, if manmade CO2 was a lever it should be more apparent in NH than SH, hence not a global issue.
Well, your theory is wrong, so there’s that.
Pictures show otherwise…
https://youtu.be/x1SgmFa0r04
It is a fact that the seasonal range in CO2 is greater in the NH than the SH, both the average and the maximum.
This essay was does with annual data for the reason show in your attached picture. The inter hemispherical forces are much stronger that the long-term climate change forces.
This concept seems plausible.
We need more data. 🙂
We do want to know what is causing less cloud cover.
“Less water evaporating from land into the atmosphere results in less clouds (less clouds, more sun).”
“When is it CRGW’s turn”
Breaking it gently: CRGW will be among those theories that dies hard and fast.
On Earth, climate change starts in the ocean. The ocean supplies the vast majority of water vapor and cloud cover and is responsible for most of the rain over land that ultimately controls the vapor pressure deficit.
It is also a massive thermal energy reservoir.
You are right the bulk of the water into the atmosphere comes from the oceans. That flux of water will change year to year if the amount of radiation absorbed changes (cloud reduction). The CRGW theory says that the clouds reduce when the relative evaporation and transpiration, ET from land is reduced (this reduction in ET% change increases the global VPD). This natural phenomenon is a series of events: lower ET% on land, mix globally, higher PVD, lower clouds, higher radiation, more water evaporation. The lower ET% on land is relative, the increase in global water is absolute.
Please pass this theory on (it may not be perfect, but it is a start), it is what is really going on since about 1970. Correct science always wins in the long run!
Am I mistaken, or do you describe Enthalpy (En) as energy (heat) content of air at various latitudes, and then measure it as a function only of temperature? Please remember that the Earth is a rotating body! “Still” air at the equator has enormous potential energy– what I call “latent KE” – as compared to “still” air at higher latitudes. Air moves back and forth across latitudes in the process of transporting energy from the hot tropics to the colder poles. The latent KE, a part of the air’s En, becomes measurable as heat, local KE, or potential energy at different latitudes. I’m not sure that static temperature measurements at various latitudes are a proper description of the complex changing atmospheric Enthalpy.
Clarification: Heat is defined as the flow of thermal energy (KE) across a temperature gradient (hot to cold).
Enthalpy in this essay is calculated from temperature and specific humidity (eq 4 above) at surface level. This essay uses annual data only. The monthly changes is En are much greater than the annual En that is related to annual climate change.
WUWT editor: typo in last sentence of first paragraph,
“. . . approaches the
duedew point the probability of cloud formation . . .”Numerous Trenberth-type calculations of Earth’s energy budget (more correctly, its long-term average power flux imbalance) performed over the last 50 years or so indicate a net power flux loss to space in the range of 0.5 to 1.0 watt/m^2 (refs: https://journals.ametsoc.org/view/journals/clim/27/9/jcli-d-13-00294.1.xml , https://en.wikipedia.org/wiki/Earth%27s_energy_budget ). This net loss represents Earth currently being in an overall multi-thousands-years-long cooling trend, which is consistent with paleoclimate proxies data indicating the Holocene Thermal Maximum (HTM), the warmest interval in current interglacial period temperatures roughly between 11,000 and 5,000 years ago with temperatures peaking around 6,450 years ago.
However, UAH satellite-derived measurements of Earth’s GLAT indicate Earth has been in a multi-decades-long warming trend since at least 1979 at an average rate of about +0.15 deg-C/decade (ref: https://wattsupwiththat.com/2025/04/05/uah-v6-1-global-temperature-update-for-march-2025-0-58-deg-c/ )
Separately, it is asserted that a 1% reduction in Earth’s average cloud coverage would result in a net increase of approximately 0.24 W/m^2 in the amount of solar radiation reaching the surface. (ref: Google Generative AI ).
So, the above article’s curve fit of “new cloud fraction data” presented in Figure 1 indicating a total reduction of about 56.5% – 54.6% = 1.9% over the interval of 1982 to 2020 would be equivalent to an increase of 0.46 W/m^2 over that time.
This would therefore be a claimed change equivalent to 50% to 100% of the calculated Earth total net power flux imbalance happening over just 38 years . . . VERY DUBIOUS.
Also, while the asserted influence of decreasing cloud fraction would be consistent with the multi-decades-long trend of Earth warming, it would inconsistent with the multi-thousands-years trend of Earth cooling since the HTM.
I suggest investigating the referenced “Climate Explorer” website as a likely source of erroneous data.
Your calculation is correct and in agreement with the CRGW theory. Note the radiation change (0.085/year W/m^2) in figure 2 extrapolated to 49 years (2024-1975) and assuming a cloud free surface albedo of 0.32 yields an increase of 2.8 W/m^2). The cloud reduction graph slope seems to be a little short as the essay suggests.
Why does fig. 3 have a cloud cover variation of 54.5 to 57% while fig.8 Is a different range of about 53 to 65 % (dropping an outlier at 69%) ? Seems to be kind of high for annual averages. One expects that sort of variation with say UAH temps where it takes a couple of weeks for the weather front/cloud variations to cross whole continents and oceans (that the satellites are polling with their sensors), then are monthly averaged….
I tend to think it is exactly the other way around. There is an increasing amount of tropospheric water vapor over land, and that’s what’s causing the observed warming. This is due to more damming and irrigation.
A perfect example is the US desert southwest. The Colorado River never reaches the sea anymore. Its entire output is distributed to farms and cities in the desert, where most of it evaporates in areas where it never would have before. This stokes the local atmosphere with latent heat that previously would have radiatively dissipated. This process is accelerating all over the world.
We have made a more humid troposphere and consequently we experience more steamy conditions. If you lived along the Denver Front Range in the ’80s, you remember those popup thunderstorms that used to drift east off the mountains every afternoon like clockwork. That never happens anymore, and I think it is due to the increased evaporation of Colorado River water changing local weather patterns.
Possibly ID, but one must do his numbers very carefully when starting with the premise that wet roads cause rain.
Wet roads do cause rain. Roads evaporate more quickly putting water vapor in the air that speeds with water cycle back to rain. A minor, fractional, impact, of course.
Wet roads causing rain is a chicken-egg phenomenon.
Wet roads are a good example of what is going on in the CRGW theory: When a road is wet it is evaporating water and the VPD is low and favorable to cloud formation, when the road is dry it is hot and the VPD is high and not favorable to clouds. The average VPD for these two conditions and the % of the earth they occupy will determine the cloud fraction probability. Low % of the earth’s surface will make them insignificant. At about 1.0% of the earth surface CRGW theory says they could become significant – size matters.
Graphs not shown are: increasing temperature and specifice humidity, SH) but a decreasing relative humidity. As figure 2 shows the VPD (from the temp and SH) is increasing – from a cloud point of view the earth is getting dryer and but holding more water in the atmosphere.
It is dew point not due point.
The warm phase of the AMO reduces low cloud cover, and the AMO is warmer when the solar wind is weaker. Every other warm phase of the AMO is during each centennial solar minimum.
Correlations of global sea surface temperatures with the solar wind speed:
https://www.sciencedirect.com/science/article/pii/S1364682616300360
That one of the reasons why annual data is used – wind speed is canceled out- it is about the same year after year.
No way, the solar wind speed varies greatly from year to year.
I struggle to understand everything that is said here but I have a question. My understanding of what the CAGW crowd is telling us is that added CO2 will cause more warming which will cause more water vapor. It is the increased water vapor plus the increased CO2 that will cause catastrophic global warming. These guys are talking about a vapor pressure deficit which leads to cloud reduction and cloud reduction causes increased temperatures due to the fact that the shortwave radiation from the sun isn’t blocked so much by clouds. So if we have a vapor pressure deficit and at the same time a higher CO2 concentration then I don’t see how more CO2 must cause more water vapor.
just one more of the contradictions inside the climate science model of how the earth’s thermodynamic system works.
CO2 concentration in the atmosphere has approached its asymptotic limit to the extent than any additional CO2 has a negligible direct or indirect (GHE) effect on global warming.
“It is the mark of an educated mind to rest satisfied with the degree of precision which the nature of the subject admits and not to seek exactness where only an approximation is possible.”
— attributed to Aristotle
The Clausius-Clapeyron relationship predicts that air can hold about 7% more water vapor for each deg C of warming, not that it will. It is an upper-bound limit, not something that will always happen. Where vegetation and water are limited, such as the interiors of large continents and the rain shadows of mountain near the coast, the water vapor is limited by low rates of evapotranspiration. Thus, the C-C relationship rarely achieves the potential because there isn’t sufficient water vapor available — what Blaisdell is calling “vapor pressure deficit.” I suspect that water vapor availability is more important than temperature. Windiness is another variable because with still air the surface above bodies of water will become saturated with vapor, which then can only leave as water molecules diffuse into the air above, perhaps assisted by convection. Additionally, wind provides kinetic energy that can strip molecules out of water and ice, so there is a relationship with windiness that I rarely see reference to.
Elevation (i.e. pressure) also plays a part, think boiling point changing with pressure. It’s not just boiling point but also a factor in evaporation and convection.
It all legislates against a pure average temperature being a proxy for anything! Unless you are a climate scientists I guess.
you got it. CO2 got nothing do with climate change.