2018/11 update: NYC is going to appeal (because they are pols).
The decision states unambiguously Climate science clearly demonstrates that the burning of fossil fuels is the primary cause of climate change, so once again the reality of GW science is not the issue. Indeed, it actually gets a teensy bit carried away IMO, continuing Global warming, or the gradual heating of the Earth’s surface and atmosphere caused by accumulation of greenhouse gas pollution in the atmosphere, has led to hotter temperatures, longer and more severe heat waves, extreme precipitation events including heavy downpours, rising sea levels, and other severe and irreversible harms. I think it is sourcing that from the complaint, which I haven't read.
The reasonning is essentially the same as in the Alsup case, and explicitly references it, which is a sensible thing to do. The headlines (and I did read the text in between) are Federal Common Law Displaces The City’s State Law Claims and The Clean Air Act Displaces the City’s Claims and The City’s Claims Interfere with Separation of Powers and Foreign Policy and the conclusion is the City's amended complaint is dismissed with prejudice in its entirety.
AFAIK, none of these rulings have addressed the cost benefit question, because they've been dismissed first. But "can you sue for damages from GW if you've been an enthusiastic burner of fossil fuels yourself?" is an obvious question, which will come into play if anyone gets any closer. And the other obvious question - who is responsible for fossil fuel CO2: those who burn it, or those who sold it - also remains.
But enough of that. It occurs to me that I've been a supporter of common law over legislation for a while now, so it would be natural to suppose me opposed to these arguments. But in this case I think the rulings are correct. Common law, as the name suggests, is there to deal with common problems, where similar situations have arisen before, and the judge's task is to discover what the law and custom says. Global warming has not occurred before within human judicial history, and attempts to relate it to previous claims under nuisance (or even less plausibly under trespass) are contrived.
So if you're feeling "disenfanchised" by the courts, what is your remedy under the legislative or executive branches? Well, obviously, to get them to pass legislation, or to act on existing legislation. "But Congress won't pass any GW legislation" you might reply, and you'd be correct, but that's rather the point, isn't it? If the will of the majority doesn't support it, you don't get it, no matter how fervently you the minority might believe in it2. And yes yes I know it is possible to argue that the public at large wants it but the evil Congress critters have been bought off by evil fossil fuel companies and so are acting against the will of the people but, whilst there is some limited truth to that, I don't think it's really the full story or even very much of it. The Joe Public is fat complacent unthinking and fond of his comforts. He is prepared to act on your minor campaigns like giving up plastic straws but inclined to regard his obligations as done once that trivia has gone by. As to the executive branch, you have Trump1, sadly.
[Update: another somewhat more parochial case by Plan B Earth (who, whilst very sweet, are probably idiots) comes my way: Environmental campaigners lose High Court battle over carbon target via a dodgy blog; or you may prefer The Graun's version. Again, I think the decision is correct: deciding the exact size of our CO2 reduction is within the "lawful exercise of [the secretary of state's] discretion". This may be a good place to remind you that I've come to think that carbon budgets are stupid, anyway.]
1. Sadly I can't find a posting by me as a good link to "Trump is a wazzock" so just take it as read: I think Trump is a wazzock.
2. Please don't interpret this as support by me for unfettered "majoritarianism", because as I've said before I'm not.
* Cleaning Out the Statutory Junk - Cato
* Supreme Court Rules on Kid's Climate Lawsuit - QS