It's the most powerful greenhouse gas known to humanity, and emissions have risen rapidly in recent years, the BBC has learned.
Sulphur hexafluoride, or SF6, is widely used in the electrical industry to prevent short circuits and accidents.
But leaks of the little-known gas in the UK and the rest of the EU in 2017 were the equivalent of putting an extra 1.3 million cars on the road.
A recent study says that often wind, solar and hydro schemes have been built inareas of environmental significance and pose a threat to key natural habitats. The authors of the report say that greater care must be taken when planning and permitting renewable facilities. "If we let these developments go ahead, the biodiversity will be gone long before climate change starts affecting it.....we are not saying that renewables are bad, we just need to put them in the right places."
European grid operators want to combine 10-gigawatt offshore turbine clusters, interconnectors and hydrogen. It no longer looks like a pipe dream.