We talk a lot about CO2 because it is the greenhouse gas that humanity produces in the biggest quantity, but there are many others that contribute to warming our planet. The refrigerant in automobile air conditioner units is one of those. It stays in the atmosphere for a long time if it leaks, and it is pretty effective at trapping heat in the atmosphere. That's why it's good news that GM, probably followed by other automakers, will start using a new refrigerant (HFO-1234yf, made by Honeywell Fluorine Products.