The warmer the atmosphere the greater the amount of CO2 it can hold is what they’re basically saying.
I would add that’s even if there has been a ‘significant’ increase. Going from something like 0.036% to 0.038% in the last 40-50 years doesn’t seem like a massive rise to me. More like someone’s taking the rise.
It’s not something I know too much about but other planets in our solar system are also going through ‘climate change’ and our ‘climate change’ is thought by some to be more to do with solar activity. It must be remembered earth is in the sun’s ‘atmosphere.’