It's assumed the viewer will be able to understand that it is the starting frame of reference, not absolute zero.

Duh — but a reference/baseline you don’t share and showing only de-contextualized change scaled to “look scary” is classic lying with statistics.

How much change does 200 ZJ represent?

We’re purposefully not told that information because that chart is propaganda meant to make an emotional argument and not informational argument — and I think it speaks to the person I was replying to that they’re using emotive arguments rather than fact based arguments.

Particularly when lobbing ad hominems at others.

There's this saying about assumptions, I forgot what it was... Anyway, it's better to be clear than make assumptions about the audience, and you know that bad charts are a big contributor to the spread of misinformation and confusion.