Controlled fusion, for the purposes of energy production, is not a solved problem. Yes, we can maintain the conditions for about a picosecond. That’s what I mean by we don’t know how to do it.

When I say it’s unlikely we’ll ever figure it out, well, that’s because the new experimental designs using plasma and huge powerful magnets are proceeding, but a single fault or destabilization in the mag fields holding the 100Mº hydrogen and the entire place will explode. Adding 100Mº to the atmosphere is a big issue, and one that’s not likely to help with global warming. The risks are too big to continue this experiment, politically. Nuclear bombs mostly destroy due to the pressure waves they create, and this explosion would rival a bomb’s destructive power... it could kill an entire city. If it ignites the atmosphere, the only thing that would save us is the low pressure of atmospheric hydrogen, which means it could exhaust it’s fuel supply eventually.