Developing a predictive understanding of feedbacks in the climate system is critical for advancing knowledge of processes and their representation in climate models. The predominant human influence is through the changing composition of the atmosphere, especially through burning of fossil fuels and increasing greenhouse gases, thereby interfering with the ability of the planet to radiate heat to space. Yet this forced component of the energy imbalance is difficult to measure quite aside from the observational difficulties owing to the large natural variability associated with day-to-day weather that constitutes a form of climate noise.

Dear Ernst

Let us review your claims.

1.Overestimation of Atmospheric CO₂ Residence Time

Fact:

• The residence time of an individual CO₂ molecule may be only a few years due to exchange with the ocean and biosphere. However, that is not the relevant metric.
• What matters is the adjustment time, or how long it takes for the perturbation (i.e., excess CO₂ from fossil fuels) to be removed.
• Studies (e.g., Archer et al., 2009) show that 20–40% of excess CO₂ remains in the atmosphere for over 1,000 years because ocean and land sinks saturate.
• Analogy: dumping water into a bathtub with a slow drain – individual drops leave quickly, but the bathtub stays full for a long time.
• Ref: link.springer.com/article/10.1007/s10584-008-9413-1

The climate impact of CO₂ is determined by its long-term influence on radiative forcing, not the turnover of individual molecules.

2. Saturation of CO₂ Absorption Bands

Fact:

• CO₂ absorption is indeed strong in some spectral bands, but not completely saturated across the spectrum.
• The wings of the absorption bands (edges of the main bands) continue to absorb infrared radiation as concentrations rise.
• Importantly, CO₂ increases the altitude of IR emission to space, which is colder at higher altitudes → less radiation escapes → net warming.
• This is well-demonstrated in line-by-line radiative transfer models and satellite observations.

The physics of radiative transfer clearly shows that each doubling of CO₂ adds ~3.7 W/m² of radiative forcing, even beyond saturation of central bands.

Ref. en.wikipedia.org/wiki/Radiative_forcing

3. Overlap Between Water Vapor and CO₂ Absorption

Fact:

• There is overlap, but CO₂ also absorbs in “windows” where water vapor is less effective, especially in the 15 µm band.
• More importantly, CO₂ is well-mixed and persistent, whereas water vapor is a feedback, not a forcing – it adjusts to temperature and has a short lifetime (few days up to 10 days).
• CO₂ initiates warming → air holds more water vapor → amplifies warming (positive feedback).
• Satellite spectra (e.g., from NASA’s AIRS instrument) directly show CO₂’s unique contribution to Earth’s IR emission spectrum.

Overlap exists, but does not nullify CO₂’s role. In fact, CO₂ is the trigger for amplifying effects of water vapor.

Ref. en.wikipedia.org/wiki/Radiative_forcing

Hope it helps

Janusz Pudykiewicz

Hi Janusz

Many years ago, we had a discussion about the lifetime of CO2 and its role in global warming. You mentioned that lifetime was about few years only. Here above I have documented different aspects of CO2 including the difference between residing time (few years) and adjustment time (few hundred years).

Hope it helps disentangling the confusion about CO2 lifetime.

Best regards

Dr. Alain Robichaud

Alain Robichaud

Hello Alain,

Thank you very much for your note. Based on the personal information that I have received from scientists at the Arrhenius Laboratory in Stockholm, in the 1980’s, we have at least two residence times to consider:

• Short term residence time: CO2 molecules emitted from the new sources remain in the atmosphere over the time of the order of around 4-5 years before being completely absorbed by the other environmental compartments.
• Long term residence time: due to the exchange with those compartments the molecules of CO2 remain in the atmosphere much longer than speculated from the short residence time. Depending on the form of the specific ocean and terrestrial models, the residence time is anticipated to be around hundreds and even thousands of years.

It is important to specify precisely which residence time is considered in your comment.

Best regards and a lot of good results in your research.

Janusz

The relationship between the magnitude of certain atmospheric model parameters and the variation of Earth's surface temperature is fundamental to understanding climate dynamics and weather prediction. Here are key parameters and how they relate to surface temperature:

1. Greenhouse Gas Concentration (e.g., CO₂, CH₄).

* Relationship: Directly proportional

* Explanation: Higher concentrations trap more infrared radiation, leading to increased surface temperature (greenhouse effect).

2. Aerosol Concentration

* Relationship: Inversely proportional (mostly)

* Explanation: Aerosols reflect sunlight back into space and can cool the surface. However, some aerosols (like black carbon) absorb heat and may warm the atmosphere.

3. Albedo (Reflectivity of Earth’s surface)

* Relationship: Inversely proportional

* Explanation: Higher albedo (e.g., ice or snow) reflects more solar radiation, reducing surface temperature. Lower albedo (e.g., oceans, forests) absorbs more heat, increasing temperature.

4. Cloud Cover

* Relationship: Complex (both direct and inverse)

* Explanation: Clouds can cool the Earth by reflecting sunlight (high albedo), but also warm it by trapping outgoing infrared radiation.

5. Water Vapor Content

* Relationship: Directly proportional

* Explanation: Water vapor is a potent greenhouse gas. More vapor increases the greenhouse effect, raising surface temperature.

6. Solar Radiation (Insolation)

* Relationship: Directly proportional

* Explanation: More incoming solar radiation leads to more energy at the surface, increasing temperature.

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the reltaionship is logarithmic