What I've been saying, probably without much clarity, is that those particular definitions are based on emotion, and are things denied by particular forms of nihilism.
The other type of nihilism related to meaning (so ignoring denial of truth and other unrelated forms of nihilism) denies certain non-emotional definitions of those terms. It's one of the main types being used in the original text.
It's not that this nihilism denies the existence of "meaning" as in "definition", or "significance" as in the way you used it with global warming. It denies specific physical scenarios, like an afterlife or a god, as well as many more. My claim, is that those physical/objective scenarios that it denies, are only put under the definition of "meaning" or "significant" etcetera because of their relation to emotion. For example, the idea of an all-loving god or eternal bliss makes people happy usually. If everyone was saddened by those ideas, rather than comforted, they would never have been described as "meaningful" or providing "purpose". By extension, someone who finds happiness in the idea of no god, or a temporary life, is someone who will not describe such an existence as "pointless" or "meaningless", but rather "meaningful". As such, I see all the forms of nihilism in the original text, as expressions of emotion alongside expressions of physical reality.
The other nihilism I see in the original text is the "everything should die/I should die" nihilism, which is separate and speaks for itself as a value judgement plain and simple. At least he doesn't use the "there is no truth" or "nothing exists" forms of nihilism.