Human Respiration is Not a Source of Carbon Emissions

That's not a problem. The CO2 that's released by humans (and animals) is produced by metabolising carbon from food, and the food comes from plants that have been grown recently. During their growth, the plants have absorbed an equivalent amount of CO2 from the atmosphere. Even when eating meat, the animals are typically only a few years old and were fed on recently grown plants. In contrast, the cars run on fossil fuels that are hundreds of million years old.