They do more than that, thank you.  Plants INHALE CO2, and exhale Oxygen.  The way to stop CO2-caused Global Warming is to PLANT TREES -- lots of trees, everywhere -- and other plants to inhale the CO2 while the trees are growing to full size.  Planting lots of plants, especially trees, will do more to stop Global Warming than all the "cap and trade" and "carbon tax" schemes in the world.