We all know that carbon dioxide – from burning fossil fuels in factories, power stations, cars and homes – is the main contributor to climate change. Some of us know that methane – from farming and landfill sites – is also an important greenhouse gas. Most people know nothing at all about a gas which is 23,000 times worse for the climate than carbon dioxide and has been used for years in electrical switchgear and even cushioned trainers.

Sulphur hexafluoride or SF6 is a human-made, colourless, odourless, non-toxic and non-flammable gas. Discovered in 1901, it is mostly used as an insulating gas in electrical switchgear but also in metal production, as a tracer gas in looking at how pollutants move about and even to drive torpedoes. It was also used in airborne military radar and as cushioning gas in training shoes when they were introduced in the late 1990s.

Sulphur hexaflouride’s environmental impact

SF6 has had a positive environmental and health impact where it has replaced the toxic polychlorinated biphenyls in large electrical transformers. Sadly it has a dirty little secret – it is an extremely potent greenhouse gas.

Scotland’s climate laws target, in addition to carbon dioxide, methane and nitrous oxide, two groups and two individual industrial chemicals containing fluorine, known collectively as the F-gases.

SF6 is the most dangerous for the climate, with a single molecule trapping as much heat in the atmosphere as nearly 23,000 molecules of carbon dioxide over a 100 year period. Once released it is expected to hang about in the atmosphere for more than 3,000 years.

Sulphur hexaflouride in training shoes

When a certain well-known brand of footwear makers realised they were selling shoes containing one of the world’s worst climate-wrecking gases they leapt into action to look for an alternative.

After more than 10 years they concluded the answer was … nitrogen. You know, the gas that makes up 80% of the Earth’s atmosphere, is the most common pure element on the planet and is the seventh most common element in the whole galaxy. You have to wonder how hard they were looking.

In Scotland, our emissions of SF6 are fortunately very small and declining. Between 1990 and 2019 emissions rose to a peak around 2000, fell quite sharply and have been running relatively flat for the last decade, with an overall reduction since 1990 of nearly 20%.

Military use declined to almost zero so the remaining challenge it to replace electrical systems that use SF6. Most uses of SF6 are in closed systems so the emissions are the result of leaks or equipment being destroyed at the end of its like, which means the actual estimates of emissions are rather uncertain.

A European law required the combined sales of the F-gases to be reduced by two-thirds by 2030 from 2014 levels. The EU is currently reviewing how well this law is working. A quota system is in operation if you want to make or sell F-gases but, because of Brexit, the law itself and its targets now need to be translated into a UK or Scottish law.

In the fight to reduce climate change emissions, every little bit helps. Unless action is taken, what looks like a tiny contribution today will look like a much bigger problem as we approach zero emissions in the future.

Dr Richard Dixon is Director of Friends of the Earth Scotland. A version of this article appeared in The Scotsman on Thursday 3 Feb 2022.