I agree they make big changes sound little; the true numbers are.Very droll, even at 400ppm of CO2 that is still a massive number of CO2 molecules, billions of tonnes, each molecule soaks up infra red radiation and then re-emits it in all directions.
5,500,000,000,000,000 tonnes, is the total atmosphere, or 5,500 trillion tonnes.
2,200,000,000,000 tonnes of C02, is 2.2 trillion tonnes. is 400ppm or 0.04% number they like
425ppm is 2,337,500,000,000 is 2.375 trillion tonnes or 0.0425% so 137.5 billion tonne increase for just 0.0025% increase, or the 25ppm above 400ppm.
if we started at 280 ppm then co2 started at 1.54 trillion tonnes that means we have added 0.797 trillion tonnes. into the air alone. not including what has been absorbed into oceans etc.
Then we have water vapour which a 1C rise in temperature can mean we see an added 7% of water vapour
Water vapor accounts for roughly 0.25% of the atmosphere by mass. so, 13,750,000,000,000 tonnes. 13.75 trillion tonnes, so adding 7% to that adds up fast.