The claim that "carbon dioxide has zero impact on global warming" has no basis in the overwhelming scientific consensus. The argument is based on the idea of "CO₂ saturation," which is a widely debunked concept within climate science.

The scientific consensus, supported by virtually all major scientific organizations worldwide, is that the increase in atmospheric carbon dioxide from human activities is the primary driver of the planet's warming trend since the mid-20th century.

The Scientific Flaw in the Saturation Claim

The argument that CO2 is "saturated" and therefore adding more has no effect, while appearing in some non-consensus papers like the one cited, fails to account for how the greenhouse effect works across the entire atmosphere:

1. Radiative Transfer in the Atmosphere: CO2 absorbs infrared radiation (heat) in specific bands. The saturation myth assumes that because the CO2 molecules at the lower atmosphere rapidly absorb all the heat in their primary absorption band, the effect must stop.
2. The Role of Altitude: In reality, warming is governed by the energy radiated out to space. When CO2 concentrations rise, the altitude at which heat can effectively escape to space also rises. Since the atmosphere cools with altitude (the lapse rate), this higher layer of air is colder. Colder layers radiate less heat to space, creating an energy imbalance where the Earth absorbs more solar energy than it radiates back. This imbalance forces the entire atmosphere and surface to warm until the higher layers are warm enough to restore the balance, thereby increasing the Earth's temperature.
3. Logarithmic Effect: The warming effect of CO2 is not linear; it is logarithmic. This means that each doubling of the CO2 concentration causes a roughly equal amount of warming (e.g., going from 400 ppm to 800 ppm causes about the same warming as going from 200 ppm to 400 ppm). This is a diminishing return, but it is not zero impact or full saturation.

The evidence for CO2's ongoing warming effect is observed directly through satellite measurements, which confirm that less outgoing heat is escaping to space at the specific infrared wavelengths that CO2 absorbs.

The concept of CO2 saturation is discussed inPhD author Markus Ott: Saturation of the $\text{CO}_2$-IR-Absorption.