As you know, there’s already carbon in the Earth. It’s part of the make up of the planet and natural events (like volcanoes) release it back into the air and as it turns out, there’s A LOT of carbon below the surface of the world but the planet is really good about regulating the natural flow. Our actions are disrupting that.
After a ten year study it was found that the planet has vast stores of carbon located in it’s crust, just hanging out, chilling. During eruptions some of this is released but the earth absorbs it back keeping things in pretty good check. There have been times of massive eruptions or asteroid impacts that have caused lots of it to be released and triggered climate change type reactions.
The current burning of fossil fuels and associated actions have caused a spike of up to 100 times greater than the planet’s natural releases meaning we are triggering another event. You may want to point out that the planet has weathered such things before so it’s NBD but, um, those past events caused mass extinctions and a host of other really unpleasant things so maybe we should work on not having a repeat.