Only if ~ is~ : inversion?

[1] *Only if we go out there and clean it up this amount of plastic is going to go down.

[2] Only if we go out there and clean it up is this amount of plastic going to go down.

You heard right. [1] is wrong.

[2] has subject-auxiliary inversion. This occurs in declarative clauses only when certain types of element are put in front position. Negatives are one very obvious type of element that trigger subject-auxiliary inversion when fronted:

"Only" is not negative, but it is semantically close to a negative, in that "Only John liked it", for example, entails "No one other than John liked it".

The answer depends on how the question is read.
Only if we go out there and clean it up, this amount of plastic is going to go down.

With the comma I added, the word "only" is equivalent to "but" or "however". That is, it's a counter point to something said in a previous sentence.

Without a comma, the meaning is equivalent to
This amount of plastic is going to go down only if we go out there and clean it up.
If that is the sense, then the original sentence should have an inversion.
Only if we go out there and clean it up is this amount of plastic going to go down.

So, is the sentence missing a comma, or missing an inversion?

A transcript in which the sentence appears shows it preceded by "Probably going to still be there in 100 years." It also shows it with the comma that I added above, so it should have the comma, and not an inversion.

CNN transcript

It is clear from the intonation in the recently provided video that the speaker's intention was the "only if" construction, and he did miss the inversion.