Hydrofluorocarbons the fastest-growing greenhouse gas (GHG) in much of the world, increasing at a rate of 10–15% per year. Hydrofluorocarbons (HFCs) are used as refrigerants, as solvents, in fire protection and in insulating foams. They are the fastest-growing greenhouse gas (GHG) in much of the world, increasing at a rate of 10–15% per year.