New Study Finds The Post-1900 CO2 Rise Has Not Discernibly Altered The Greenhouse Effect

Variations in the greenhouse effect are predominantly modulated by water vapor and cloud cover. CO2’s role in the greenhouse effect is so minor it cannot be discerned.

For decades scientists have reported that a CO2 concentration of about 300 ppm can only increase the downwelling longwave radiation (DLWR), or greenhouse effect, by about 1.5 W/m² at the surface. See, for example, the complementary studies by Ramanathan (1981) and Newell and Dopplick (1979).

“The infrared flux dominated by CO₂, as is well known, is only about 10% of that controlled by water vapor. The decrease in infrared flux from the surface to the atmosphere due to the increase in CO₂ ranges from 1.0 – 1.6 W/m².” – Newell and Dopplick, 1979

With the total DLWR value assessed as ~330 W/m² , this means that CO2’s 300 ppm (~1.5 W/m²)  impact can only enhance the greenhouse effect by around 0.5%. Nearly all the rest is dominated by water vapor (and cloud).

“Carbon dioxide…increasing downwelling LW radiation by ~1.5 W/m². It is about 0.5% of the 327 W/m² of overall downwelling radiation that warms the Earth’s surface. The vast majority of that warming is contributed by water vapor. Together with cloud, it accounts for 98% of the greenhouse effect.”  – Physics of the Atmosphere and Climate (textbook)

Image Source: Salby, 2012 (pg. 249)

Using DLWR data from 71 globally distributed sites, Koutsoyiannis and Vournas (2024) assessed the post-1900 increase in the CO2 concentration (from 300 ppm to 420 ppm) and found that it “has not altered, in a discernible manner, the greenhouse effect.”

If CO2 concentration increases were to enhance the greenhouse effect – and thus be considered the driver of modern warming – there should be a change in data point distribution (displacement) in alignment with CO2 increases along the equality line as shown in the DLWR data set chart (Figure 2). This has not occurred.

“An enhancement of the greenhouse effect, due to increasing CO2 concentration, through the years would be seen as a gradual displacement of the points from left to right with the progression of time. However, the alignment of the points of the different data sets does not show a gradual displacement from left to right. This means that the effect of the direct CO2 emission at the surface is smaller than the side effects…causing the variability in Figure 2, and thus it is impossible to discern.”

Image Source: Koutsoyiannis and Vournas, 2023
In fact, the opposite of what should happen with an enhanced greenhouse effect has been slightly more discernible in data sets. All-sky (clouds included) DLWR trends at the top of atmosphere (TOA) have actually been shown to be declining in 21st century CERES observations, as they are “slightly negative for all-sky.” In other words, the 2000-present greenhouse effect has been weakening despite increasing CO2 concentrations.
Image Source: Koutsoyiannis and Vournas, 2023

The declining greenhouse effect observed in recent decades has been reported by many other scientists.

“…the negative trend of G [greenhouse effect anomalies] indicates that the atmospheric greenhouse effect is temporarily [1985-1999] decreasing, despite the fact that greenhouse gasses are increasing.”  – Cess and Udelhofen, 2003

If the greenhouse effect has not been enhanced since the 1980s, it cannot be responsible for modern warming.

10 responses to “New Study Finds The Post-1900 CO2 Rise Has Not Discernibly Altered The Greenhouse Effect”

  1. John Hultquist

    We are not doomed then, despite headlines to the contrary.

  2. Harry
  3. Mike Gilding

    I am puzzled. If CO2 can reverse the direction of photons released from the Earth, why can it not also reverse the more numerous photons aimed at the Earth. Thus, reducing the Earth’s temperature?

    1. Chris

      ‘cos not all photons are the same. Incoming photons are much higher frequency than those released from the Earth.

  4. Denying Scientific Principles – Newsfeed Hasslefree Allsort

    […] New Study Finds The Post-1900 CO2 Rise Has Not Discernibly Altered The Greenhouse Effect […]

  5. John Jaeger

    If the Climate Change Cult is so obsessed with “sustainability,” why don’t they move to Cuba, the only country on earth listed as “sustainable”? Beans and rice for every meal, no vacations, no fun. No need for Cultists to glue their hands to highways to ruin everyone else’s day.

  6. historyscoper


    Solar photons are high temperature (5500C) and short wavelength (0.4-0.8 microns). They travel through Earth’s atmosphere almost unhindered to the surface. It’s the long wavelength IR photons emitted by Earth’s surface to cool from the solar photons that atmospheric CO2 can “reverse the direction of”.

    All day the surface absorbs solar photons and slowly heats up via its heat capacity of so many degrees per Joule. At the same time it tries to cool by emitting IR radiation based on the black body radiation law, with peak power at a wavelength inversely proportional to the absolute temperature T independent of material, and a total power over all wavelengths proportional to T^4.

    Until the surface gets really hot, the surface cooling IR has low power. The hotter it gets, the higher the cooling power, keeping surface temperatures normally below 50C even in Death Valley on July 4. The normal Earth surface temperature range is -50C to +50C, corresponding to peak power wavelengths of 8-13 microns. Magic CO2’s absorption/reemission wavelength is way out at 15 microns, so cold (-80C) that it’s not even heat, and can’t raise the temperature of any black body absorbing it higher than -80C, which means almost never.

    The big con game of the global Marxist politician-run U.N> IPCC is to pretend that that atmospheric CO2 molecules catch and regurgitate 15 micron IR surface cooling photons to add to the solar photons and raise the temperature higher than the Sun alone, when they came from the surface in the first place, meaning they’re double-counting them to make CO2 seem like a magic global warming gas for pure political gain. The fact that 15 microns is the peak power wavelength of an iron rod chilled to -80C is denied by them, because their whole scam is a denial of Nature’s ironclad First Law of Thermodynamics (energy conservation) and Second Law of Thermodynamics (entropy).

    Forgetting about the Second Law, once you see it, energy double-counting that denies the First Law is as plain as the nose on Jimmy Durante’s face. It’s a misdirection play like stage magicians and carnival grifters pull. All these years they’ve misdirected millions, even physicists, to sell their CO2 hoax and stir enough alarm to swindle billions if not trillions of taxpayer money.

    It’s time the good news is spread that the IPCC emperor has no clothes so that it can be laughed out of business and their gigantic steal stopped. They enjoy enormous control of Big Tech and the PC press, but if we try hard enough the truth can spread enough to sink them and their big plans to eat the world.

    It sounds like I’ve trivialized a complex problem, but yes, I have. It’s so simple a 5th grander can understand it. Here’s the complete disproof of the greenhouse effect in a link that all should share if they care about their children’s future:

    Truth trumps politics. Screw Marx.

  7. Richard Greene


    That is the longest junk science comment I have read this year.

  8. Richard Greene

    Adding CO2 to the atmosphere along with the water vapor positive feedback CErTAINLY increased the greenhouse effect.

    the traditional methodology for measuring the greenhouse effect is simple but not accurate. An excellent article at WUWT discussed poteNtial errors in claimed greenhouse effect measurements

    We know there is a greenhouse effect and CO2 is part of it.

    We know the greenhouse effect must increase from more CO2 emissions.

    But the effect of MORE CO2 can only be estimated fRom lab spectroscopy measurements.

    the actual effect PF MORE CO2 in the atmosphere can’t be accurately measured because there are too many other climate change variables for which we do not have accurate measurements.

    Based on lab spectroscopy, CO2 x 2 should cause about +.5 to +1.7 degrees global warming/

    If we assume CO2 caused all the global warming since 1975, (not likely) we get a similar worst case ECS for CO2.

    The Russian INM model assumes a +1.8 degree C. ECS for CO2.

    The best science we have points to a relatively low ECS of CO2 that will harm no one.

    The false claims there is no greenhouse effect, or CO2 does nothing, or manmade CO2 emissions only accounted for 3% of total atmospheric CO2, are all junk science that lead to many conservatives correctly treated as science deniers.

    The bottom line is we added a lot of CO2 to the atmosphere, and that’s why plants grow better and colder nations have had more moderate winters than in the 1970s. More CO2 is good news for plants. So is global warming fgood news or most people

    Cold weather / climate is bad news

    All we know about the future climate is that it will be warmer, unless it is colder. Let’s hope for warmer.

  9. historyscoper

    @Richard Greene

    [[That is the longest junk science comment I have read this year.]]

    I’m teaching true science. The U.N. IPCC octopus blasts way longer junk science diatribes worldwide 24/7/365 to sell its demands for money and power.

    If I’m spewing junk science, where’s your scientific refutation? A bigoted brain fart doesn’t qualify. Are you an official IPCC spokesperson? The entire IPCC version of climate science is junk science, as is yours.

    The longest what? I’ve published over a thousand articles on Quora tearing the U.N. IPCC octopus apart on every level, and so far no attempts at a scientific refutation, just shadow-banning and smearing because that keeps their gravy train going.

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