It's still misleading. a naive glance would make someone think co2 levels had risen to 800% of original value, when it's only 150% of original (which is obviously still terrifying)

I disagree. Clearly the absolute amount of CO2 is more important than the relative change.

It would have much more impact and be less misleading if they started at 0.

Not starting at 0 both lets people dismiss the graph because they used the stupid not-starting-at-zero trick, and it hides the fact that CO2 concentration has increased by 50% which is insane!