This suggests that there might be active volcanoes on Venus that we haven’t identified. If we can’t identify eruptions directly, that raises the possibility that our failure to identify active volcanoes doesn’t guarantee the absence of active volcanoes on Venus.

It’s not clear what a short-term spike 30 years ago has to do with the short-term spike detected recently.

We detected a short-term spike in sulfur dioxide on Venus. Comparative levels of sulfur dioxide on Venus and Earth don’t shed light on the cause of a short-term spike.

This suggests that traces of sulfur dioxide can last a long time from volcanoes. But this doesn’t explain a short-term spike in sulfur dioxide. We’re not just trying to explain the presence of sulfur dioxide in the atmosphere; we’re trying to explain a short-term spike.

If anything, this might strengthen the author’s argument by suggesting another explanation for the short-term spikes on Venus besides volcanoes.