This seems like something Chat Gippity might actually be of some value:

The CO₂ exhaled by a person riding a bike is tiny compared to a car’s emissions. Let’s break it down:

Human CO₂ Emissions from Biking

• A resting human exhales about 0.7 kg of CO₂ per day (~29 g per hour).
• Moderate cycling increases breathing rate, and a cyclist might exhale around 4x more CO₂ than at rest.
• This comes to ~116 g of CO₂ per hour.
• A cyclist at 20 km/h would emit ~5.8 g of CO₂ per km.

Car CO₂ Emissions

• The average gasoline car emits ~200-250 g of CO₂ per km.
• Even efficient cars emit over 100 g of CO₂ per km, which is still far more than a cyclist.

Comparison

• A cyclist exhales ~5.8 g CO₂ per km.
• A typical gasoline car emits ~200 g CO₂ per km.
• A cyclist produces ~30-40 times less CO₂ than a car per km.

Even when considering food production emissions for fueling the cyclist, biking is vastly cleaner than driving.