Is it even a proper burnoff if you don’t either singe the eyebrows or end up with a visit from the fire brigade?

I would’t worry about the CO2 from it too much, if you used it as mulched or composted it the same amount of CO2 would be released, just over a bit longer timeframe. The small particle polution on the other hand, that can be a bit of a problem. Although only really in aggregate with lots of people doing it.