The process of burning fossil fuels and turning them into CO2 is called combustion.

Here's a breakdown:

* Fossil fuels are hydrocarbons (made of hydrogen and carbon) formed from the remains of ancient organisms.

* Combustion is a chemical reaction that involves the rapid reaction between a substance with an oxidant, usually oxygen, to produce heat and light.

* When fossil fuels are burned, they react with oxygen, releasing carbon dioxide (CO2), water (H2O), and energy in the form of heat and light.

So, while the final product is CO2, the process itself is combustion.