Here's why:

* Photosynthesis is the process where plants, algae, and some bacteria use sunlight, water, and carbon dioxide to create their own food (glucose) and release oxygen as a byproduct. In this process, carbon dioxide is taken in and used to build organic molecules.

Here are some processes that do return carbon dioxide to the air:

* Respiration: All living organisms, including plants, animals, and bacteria, respire, which means they break down food to release energy. This process releases carbon dioxide as a byproduct.

* Combustion: Burning fossil fuels (like coal, oil, and natural gas) releases carbon dioxide into the atmosphere.

* Decomposition: When organisms die, they decompose, breaking down organic matter and releasing carbon dioxide.

* Volcanic Activity: Volcanoes release carbon dioxide from the Earth's interior.

Let me know if you'd like to explore any of these processes in more detail!