[cogman10]

> It would be quite odd if the CO2 fertilization effect has already peaked, given that geological history shows periods with much higher CO2 concentrations, during which plant growth was significantly greater.

The species of plants were at a different evolutionary stage. Further, a lot of bio matter wasn't in the form of human consumables. Algae was by and large the main CO2 absorber of prehistoric periods.

It took millions of years of growth for plants to sequester the carbon we are currently emitting. That's millions of years of adaptation to the ever changing atmosphere composition.

[ETH_start]

ChatGPT:

The optimal CO₂ concentration for plant growth in greenhouse farms typically ranges between 800 and 1,200 ppm (parts per million). Some high-intensity commercial greenhouses may use levels up to 1,500 ppm, but beyond that, the benefits diminish, and excessive CO₂ can start to have negative effects.

The current atmospheric CO₂ level is approximately 420–425 ppm as of 2024, which is significantly lower than the optimal greenhouse levels for plant growth but much higher than pre-industrial levels (~280 ppm).

--

Worth noting that at 1,000 ppm, CO2 begins to impair human cognition, and if we really want to be safe, we really shouldn't allow it to even get close to that, e.g. 700 ppm is probably already cutting it too close.

[cogman10]

Here's what a university has to say on the matter [1]

The gist of it, CO2 supplementation can be beneficial to some plants (not all plants) IFF you also tweak all other inputs into growth. Not something that happens outside of a greenhouse.

> Plants may not show a positive response to supplemental CO2 because of other limiting factors such as nutrients, water and light. All factors need to be at optimum levels.

[1] https://extension.okstate.edu/fact-sheets/greenhouse-carbon-...

[ETH_start]

Well, plant growth on Earth massively increased in the 30 years up to the 2016 study. It would be quite the coincidence that it stopped right after that study.