The evidence keeps piling up. Climate sensitivity to an increase in atmospheric CO2 is effectively zero.
Scientists Hermann Harde and Michael Schnell published a paper in 2021 entitled “Verification of the Greenhouse Effect in the Laboratory.” The study alleged to experimentally determine the atmospheric CO2 greenhouse effect not only exists, but functions in concert with physical laws.
“To our knowledge we present the first demonstration of the atmospheric greenhouse effect in a laboratory experiment, which also allows quantitative measurements under conditions as in the lower troposphere. We use an experimental set-up consisting of two plates in a closed housing, one plate in the upper position heated to 30°C, the other at the bottom and cooled to -11.4°C.”
A few years later Thorstein Seim and Borgar Olsen (2023) analyzed their experimental setup in further detail. They noted that when the CO2 is increased 500-fold, or from 0.04% (400 ppm) to 20% (200,000 ppm) in the Harde and Schnell greenhouse effect experiment the plate temperature increases by just 1.18°C, and by just 0.4°C more (1.6°C total) when the CO2 concentration reaches 100%.
Image Source: Seim and Olsen, 2023
But in their 2023 paper Seim and Olsen modified the Harde and Schnell (2021) experiment to better simulate “the earth/atmosphere situation.” They found that instead of modestly increasing the plate temperature by a little more than one degree, their tweaked experimental setup showed increasing CO2 from 0.04% to 100% actually cools the blackbody (plate) by about -0.2 to -0.3°C.
And now, in another new lab study, Harde and Schnell, 2025 provide experimental evidence that further supports this negative (or near-zero) greenhouse effect at high CO2 concentrations. Their experimental setup shows increasing CO2 from 20,000 (2%) to 80,000 ppm (8%) leads to a negative greenhouse effect, resulting in tenths-of-a-degree cooling.
This may be the second experiment to illustrate the negative greenhouse effect in a lab. Radiation studies published by other authors (Schmithüsen et al., 2015, Chen et al., 2024) also indicate the cooling influence from adding CO2 may occur in polar climates (Antarctica, Arctic). A CO2-induced high-latitude negative greenhouse effect fully undermines the anthropogenic global warming (AGW) narrative that says humans are driving “polar amplification,” or rapidly melting glaciers, ice sheets, and sea ice.
“CO2 radiation is measured for three standard concentrations of 2, 4, and 8%. Addition of CO2 leads to a significant cooling of the gas temperatures…”
The latest Harde and Schnell study also affirms water vapor (WV) dominates the greenhouse effect (GHE), and thus the assumption that CO2 is a driver of greenhouse effect forcing has “significant limitations.” Unlike the 2, 4, and 8% CO2 volumes utilized in this experiment, the real-world atmosphere, with 0.042% CO2, is overwhelmed by WV concentrations that are 30-40 times greater. Thus, the saturated absorption bands where CO2 could potentially have an effect are “overlaid” or “overlapped.”
“[D]ue to the long propagation paths in the atmosphere and the 30-40 times higher WV concentration, the weak overlap of the spectra leads to a significant limitation of the CO2 climate sensitivity…”
“As the H2O concentration increases, the gas radiation of the other GH-gases is overlaid, and their effectiveness is correspondingly reduced.”
Image Source: Harde and Schnell, 2025
It is assumed that the 100 ppm (0.01%) atmospheric CO2 increase since 1950 – from ~320 to 420 ppm – has been the primary cause of 1950-to-present global warming. However, these experiments show increasing CO2 2500-fold (0.04% to 100%) or even 100-fold (~40,000 ppm) leads to insignificant warming or even tenths-of-a-degree cooling. This tiny thermal impact is too insignificant to measurably affect Earth’s climate.
I’ve been saying this for a long time. Polyatomics are net atmospheric radiative coolants. It is the monoatomics and (to a lesser extent) homonuclear diatomics which are the closest we come to “greenhouse gases” (in the strict ‘actual greenhouse’ sense, not the fake “greenhouse effect (due to backradiation)” sense of the climate alarmists).
In fact, I derived the Specific Lapse Rate (SLR… what the Adiabatic Lapse Rate (ALR) would be if the atmosphere consisted of only that gas) of 18 of the most-common atmospheric gases (then cumulated each SLR in accord with the concentration of that gas, to arrive at the dry ALR… as a double-check of my math), and figured out how to calculate the resultant change in atmospheric temperature gradient (and thus surface temperature) for any given change in concentration of any given atmospheric gas.
I calculate the “ECS” (the change in lapse rate temperature gradient… because AGW / CAGW is a fiction, and that leaves only the ALR) of CO2 to be 0.0000116834261823 K km-1 ppm-1.
https://www.patriotaction.us/showthread.php?tid=2711
Yet other studies showing that the CO2 can’t do anything significant to the global temperatures.
There is also a simple way to show this with a cross-correlation diagram or a simple correlation analysis using the last 45 years of CO2 concentration (from Mauna Loa) and global Temperatures (from UAH).
The result is that the correlation (and the cross-correlation CO2 -> T) are negative (not significantly, but nevertheless negative).
So, if CO2 was a significant cause of T variation, it wouldn’t have a warming effect, but rather, if anything, a cooling effect.
Thus, the very assumption that a CO2 concentration increase may be a cause of the global temperatures increase is proven wrong.
Those findings are consistent with the Annual Earth Energy Budget (see NASA or the IPCC) which shows that active gases in the infrared spectrum absorb some 20W/m² from what is emitted by the ground and emit some 160W/m² into space, thus, in conjuction with atmospheric convection/advection cells, they have an average cooling effect on the atmosphere of 140W/m², which destroys the GHG hypothesis.
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How about a planetary experiment like Svante Arrhenius originally proposed in the 1890s as impossible? It’s been actually done: read and heed: https://t.co/SgWzeWz5WE
The summary is about how the temperature of the lower plate decreases.
This is natural, since some of the radiation energy is absorbed in the gas. The plate will cost less.
The atmosphere is what heats up better. Modeling this:
– reduction of upper plate heat dissipation to zero – no heat conduction towards outer space, vacuum,
– exact measurement of gas temperature,
– measurement of the radiation energy of the gas towards the lid,
I didn’t see it. It may be that is, but then you should write about it in the summary.
The heat source shouldn’t be thermostatically controlled, it should be at constant power. When heat absorption in surroundings of the heat source increases it should lead to cooling of the heat source if power is constant. Earth has a constant power source, it’s not thermostatically controlled.