What do you think will happen if we continue to destroy the world's rainforests?

CO2 levels will dramatically increase as well as food level supply will decrease. Oxygen levels will decrease too.

Explanation:

 Plants take in CO2 and produce Oxygen. Without plants, they can't take in CO2, and it is a necessity for them to take it in. Plants would die. Food supply would decrease because plants produce glucose during photosynthesis. Glucose is a kind of natural sugar that will be lost. Plants produce fruits or vegetables, so if there are no plants then no food.

Hope this helps!

when you breathe in, or inhale, your diaphragm contracts (tightens) and moves downward. this increases the space in your chest cavity, into which your lungs expand. the intercostal muscles between your ribs also enlarge the chest cavity. they contract to pull your rib cage both upward and outward when you inhale.