That's just stupid, even if you accept anthropological global warming at face value.
The CO2 humans exhale comes from carbon ingested as food. Which was very recently captured by a plant preforming photosynthesis, with maybe some other animals between you and the plant. In any case, the global warming concern involves taking carbon which has been sequestered in the ground on geological timescales, and rapidly adding it back to the biosphere. Carbon moving around within the biosphere is not, as I understand it, a concern.