Learn French: Nous dénonçons le fait que le réchauffement global soit rapide. - We denounce the fact that global warming is fast.

The phrase le fait que (the fact that) introduces a subordinate clause. Even though a "fact" seems certain, when the main verb expresses a judgment, emotion, or opinion (like nous dénonçons), the subjunctive is required. The sentence focuses on the subjective reaction to the fact rather than just objectively declaring it.

Does le fait que always trigger the subjunctive?

It almost always does in everyday French. While you might occasionally see the indicative if the sentence is neutrally declaring an objective reality (such as after c'est un fait que), when le fait que introduces a fact that you are judging, regretting, or denouncing, it strongly requires the subjunctive.

Is réchauffement global the standard term for global warming?

It is perfectly correct and understood, but le réchauffement climatique is actually the most common and natural-sounding term in French media and daily conversation for both "global warming" and "climate change."

Could I say soit vite instead of soit rapide?

No, because you need an adjective here. Rapide is an adjective describing the noun phrase le réchauffement (the warming is fast). Vite is an adverb meaning "quickly," which is only used to describe how an action is performed (for example, il court vite).