I think you mean "probability" rather than severity. The severity of setting the atmosphere on fire is extreme, but the probability turned out to be vanishingly small. Or perhaps you mean risk, probability times severity. Which also turned out to be negligible for the events in the article.

Some other hyped risks: -

- Artificial General Intelligence

- CRISPR gene editing

- Gain-of-function work with viruses

I have no way of assessing the risks, and there is a lot of hyperventilation in some circles