Fire-pits are the worst!
Fuels lock away carbon and burning releases it back into the atmosphere.
Carbon dioxide is a direct product of burning fuel. Here is an interested comparision of different fuels and the CO2 that they release when burnt.
In a nutshell, if you need to burn something to keep warm then modern burners release the least amount of carbon back into the atmosphere and wood burnt on an open fire or garden fire pit releases the most. Almost the same amount as 3 people smoking 20 cigarettes.
