We often villainize carbon dioxide, thinking of it as the enemy in our fight against climate change. But in doing so, we forget the essential role it plays in our ecosystem. Plants need CO2 to photosynthesize, and almost all other organisms depend on the energy from this process to live. If you look at anything living or once living—from a tree branch, to a celery stalk, to your own body—you are looking at something that is storing lots of carbon.