To visualize what your comment is saying, a green garden pea dropped in an empty 5 gal bucket fairly represents to ratio of CO2 to the entire atmosphere.
Anyways, CO2 is just fertilizer which plants use to produce more oxygen.
How about 100% of the atmosphere visualized in a monetary format...a dollar equals one percent:
Imagine $100.00 in pennies in rows on a large table. That's 10,000 pennies.
Paint four of the pennies green. (CO2 = 4/100ths of a percent)
Using the 4 green pennies, form a layer to trap heat!
Scatter them throughout the "atmosphere"...they can't even see each other.