“Slight warming of the air is also observed with [100,000 ppm] CO2 but is close to the temperature resolution of the sensors with ±0.1°C. Given an approximately 400 times lower CO2 concentration in the atmosphere, this warming is likely negligible.”  – Schnell and Harde, 2026

New lab experiment research shows that the addition of 100,000 ppm (10%) CO2 – a volume orders of magnitude greater than today’s 425 ppm (0.0425%) – leads to a temperature change of about 1.0°C.

(Interestingly, the experiment shows this magnitude of temperature change can also be accomplished by adding argon (Ar), a non-greenhouse gas, and hydrocarbon gas (HCG), a propane/isobutane mixture.)

“With an initial temperature of the earth plate of +30°C, a temperature increase of 1.0°C can be observed after adding [100,000 ppm] CO2.”

But this CO2-induced (or Ar or HCG) temperature change (~1.0°C) is accomplished when assessing only radiation heat transfer effects and excluding the effects of convection. In the real world, heat is not transferred solely via radiation. In fact, convection, not radiation, dominates the heat transfer process here at the surface and throughout the lower troposphere.

So when convection is included as a contributing factor in these lab experiments (see also Wagoner et al., 2010 or Seim and Olsen, 2020), the temperature effect of adding 10% CO2 is reduced to just 0.1°C. This temperature change is so negligible that it is effectively below the resolution of the measurement sensors.

The real-world atmosphere has convective heat transfer dominating and 100s of times smaller CO2 concentrations than in this lab experiment. Thus, it can be concluded that the climate sensitivity to even a massive CO2 increase is effectively zero.

“HCG [hydrocarbon gas] causes a cooling of 2.5°C without convection, compared to only 1.3°C with convection; CO2 [100,000 ppm] leads to a cooling of 0.8°C compared to 0.1°C with convection. This shows that convection is a dominant heat transport mechanism that reduces the radiative effect.”

“When convection is allowed, greenhouse gases only slightly reduce the radiation reflected from the dome to the warm plate, causing a slight cooling, and correspondingly, only a slight decrease in the radiation emitted to space.”

Image Source: Schnell and Harde, 2026