To set up a control group, you pick individuals at random( so you don't just get a group to be of the same character, or opinion).
The control group is vital in every experiment because, sometimes our hypothesis could be mere coincidence or assumptions. So the control group will be compared to the test group to see if the results are correct. Plus look at it this way, without a control group, your hypothesis wouldn't be a theory.
CO2 molecules can vibrate in ways that simpler nitrogen and oxygen molecules cannot, which allows CO2 molecules to capture the IR photons. Greenhouse gases and the greenhouse effect play an important role in Earth's climate.
