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.
Levels are rising as an unintended consequence of the green energy boom. Cheap and non-flammable, SF6 is a colourless, odourless, synthetic gas. It makes a hugely effective insulating material for medium and high-voltage electrical installations.
It is widely used across the industry, from large power stations to wind turbines to electrical sub-stations in towns and cities. It prevents electrical accidents and fires.
However, the significant downside to using the gas is that it has the highest global warming potential of any known substance. It is 23,500 times more warming than carbon dioxide (CO2).
Just one kilogram of SF6 warms the Earth to the same extent as 24 people flying London to New York return.
It also persists in the atmosphere for a long time, warming the Earth for at least 1,000 years.