Well, not quite 'coz remember, anything in Nature is in great balance that volcanic eruptions are actually needed to sustain life in this planet. (This is a long story that's too long to explain here but just remember, CO2 does sustain life as long as there's not too much of it & that anything in Nature is in great balance.)

Thus, even if volcanic eruptions emits a lot of CO2, they occur only every hundred years or so giving nature time to absorb it thereby providing a source of life for the environment while also cleaning up the atmosphere.

However, man's emission of CO2 via his engines & industries is non-stop! And ultimately, it adds a great deal of burden to Nature - a burden that Nature doesn't need & sooner or later, will OVERWHELM it.