Even if it's too late to avert many of the consequences of climate change, even if we act far more decisively than we're likely to act, one thing I wonder is, what would happen if humanity died out tomorrow?
(Well, let's not bum out everyone's holidays, let's have us die out in January, I guess.)
I mean sudden and complete extermination, with no other effect. Feel free to posit something suitably gruesome, but to avoid mucking up the question with nuclear fallout or anything, let's say it's a super-fast, super-virulent plague that crosses the globe in a few hours. Everyone dies too fast to do anything stupid, so the world is just left to fend for itself.
I am not enough of an expert in climate change or meteorology to offer anything more than a wild guess about what would happen. A lot of mankind's technology would keep running for hours, days, weeks, some of it for months. But carbon emissions would plummet. While some unattended things would cause greater pollution than while they were attended, for a while, most things would stop running or stop producing emissions fairly quickly. I'd guess that within a week, carbon emissions and all other forms of pollution would have dropped off to a percent of current levels or less.
A few very splashy incidents of pollution, as unattended power plants, factories, dams, etc. broke down would cause some heavy devastation, but the most dangerous of those would shut down quietly on their own without anyone running them, and even the worst of those would not amount to a fraction of the damage we do to the world each day when things are working fine. And after a week or three, those would have run out, there'd be fewer and fewer exploding plants and huge leaks.
But since the energy pipelines of the climatological systems are long and broad, the climate would probably keep warming for at least a few decades. However, I tend to think, and again this is wild conjecture, that the biggest impacts would be largely averted. There would still be climate change but it would not be intense enough, or long-lasting enough, to exceed the abilities of most species to adapt to it.
None of this would change if, to make the scenario more interesting (at least to roleplayers and authors), a handful of humans survived in the post-apocalyptic (but in this case, more pleasant than pre-apocalyptic, in some ways) world, getting by on stocks of canned food, bottle water, and eventually on a few crops and hunted game, living in the ruins of Walmarts. One could even posit that, after a hundred years, this small seed of humanity could start to rebuild their numbers and even vestiges of their civilization from the ruins.
Supposing they didn't also forget where they came from (their Kindles and iPods would still work as long as they could find another box of batteries somewhere, and they could still read Wired and the New York Times, so I doubt the mass amnesia of 80s post-apocalypse movies would settle in within two generations), they could even start to rebuild some basic technologies. It would be many decades or centuries before they had power plants working (or enough people either to man or use them) but they would eventually have some technology with the capability to cause pollution and carbon emissions. Would the world have recovered enough that, provided they didn't make the same mistakes right away, they could avoid recreating the oncoming climate change catastrophes? Obviously, provided they didn't learn from our lessons, they would eventually get to enough people and enough advancement to recreate the conditions, but after how many generations?