This win is dramatic, to say the least, as a common law basis for a right to a safe climate may be established in the US. Several states have a clean environment clause in their constitution, which are now open to climate-centered interpretation in light of this ruling. The American people may finally have legal recourse against environmental degradation and climate destruction. This is a huge win for the planet.
The reasoning was highly suspect in this ruling, with the state's assessment of this being a publicity stunt having only a kernel of truth to it. Montana's role in climate change is infinitesimally small, with the plaintiffs trying to get a remedy the court simply cannot provide. This reasoning will not withstand scrutiny nationwide, as it's legislatures, not the legal system, that establish environmental regulation.