One of the big selling points of SF6 equipment has been that it's more compact size and higher electrical efficiency, actually results in lower global warming, because the CO2 savings from improved efficiency outweigh climate effects from escaping SF6.

The counterpoint is that unless properly maintained the equipment may develop unacceptable rates of leakage - and that this may be happening in a widespread fashion.

That SF6 is a serious problem is well known - in the 1997 Kyoto protocol, it was named as 1 of the 6 main greenhouse gases, and it is regulated by governments across the world because of this. Extensive research into alternatives has also been performed since that time.

That SF6 is so good is part of the problem - it has proved extremely difficult to find alternative gases which have similar performance, and which could be used in similar equipment. The last 2 or 3 years have seen some significant progress, with a number of potentially viable alternatives being named such as 2,3,3,3-tetrafluoro-2-(trifluoromethyl)propanenitrile which is approaching commerically ready. The alternatives are much better, but have the disadvantage of toxicity, significant GWP (but nowhere near as high as SF6), and as perfluoro-compounds are potentially "forever chemicals".