Apparently 8%. But all of these industries waste it unnecessarily, due to our failing to price in or consider the future scarcity.
Helium as a waste product of fusion reactors is such a pipe dream, and will produce such tiny volumes should that ever happen, that it is not a remotely realistic solution to the problem.
(*) I'm more or less convinced that such a miracle technology is the only hope we have of avoiding catastrophic change. I'm baffled why there's not massively more funding into researching potential geoengineering solutions, given the stakes. Even fossil fuel companies would benefit!
What we do use helium for today are things like MRI machines that are medically invaluable, and we do so wastefully potentially denying future generations this technology.
Even if we eventually find alternatives, it may be inferior or we may otherwise deny them technological advantages of similar importance that would be more accessible through access to helium.
The problem is that today Helium is cheap enough we’re happy to boil an MRI machine’s worth off into space for a child’s birthday party.
Climate change is simply another face of the same coin of indifference to the costs we confer on others.
Apparently there's plenty on the moon...