How it all could end
We know that Season 7 concludes with the dramatic destruction of the Wall, the last defense keeping the White Walkers from running rampant all over Westeros. It's a chilling image that creates the kind of "we're fucked" feeling dominant in discussions of climate disaster, and this quote from the work of Charli Carpenter -- as pointed out by Vox and other outlets -- indicates the race to the finish line could directly comment on the climate change theory:
"The slogan 'Winter is coming' is meant literally as well as metaphorically: planetary forces are moving slowly but inexorably toward climatic catastrophe as the infighting among kings and queens distracts them from the bigger picture. This is a collective action story, with the Night’s Watch issuing increasingly desperate alarms yet receiving indifferent shrugs. ...The argument [of the series] seems clear: if existing governance structures cannot manage emerging global threats, expect them to evolve or fall by the wayside."
A "collective action" story sounds a lot like the alliance between the First Men and the Children of the Forest, and is a lot more hopeful than the reputation of Game of Thrones suggests. Following Carpenter, the endgame of Game of Thrones will depend not upon who sits on the Iron Throne, or who screws whose aunt, or who finally stops Cersei's ascent to the the title of Mad Queen, but on whether or not the various forces of humanity that still have money, military, magic, and magnificent dragons can get past their realpolitik and cooperate long enough to fight the forces of evil that are capable of changing the weather.
Maybe Jon Snow will survive long enough to pull it off and eventually prevent a second Long Night, as has been prophesied in the saga. Or maybe, to borrow a metaphor real-life climate scientists have used, our characters have gone "past the point of no return," and their squabbling, wasted time, and the disruption of a natural order have caused an irreversible dent in humanity's ability to confront an inevitable devastation.
The "point of no return" is a fitting description because it sets up the moral dilemma all of the saga's main characters will face before the end: Do you continue to address the difficult long-term problem like Jon Snow, who faces the danger, knows the danger, has been outnumbered by the danger several times over, and chooses to fight anyway? Do you battle against climate change even though we're "past the point of no return"? Or do you focus on a chair made of swords and your control over people and nations, while your population and countryside freeze over?
If that devastation is inevitable -- and, again, Game of Thrones is not known for hopefulness -- ice will envelop the land before the end of the final season. The Wall has fallen. Daenerys Targaryen will die. Jon Snow will die again. They will return as cold carcasses, perhaps missing an ear, an eye, an arm, but no less certain of their dark, singular mission of destruction. Perhaps Sansa will live to watch the frozen, desiccated corpses of babes feast on the flesh of those still living in Winterfell, before a wight that was a Stark turns her into a frigid specter, too. And perhaps even the two remaining dragons, the Song of Ice and Fire's symbol of hot-blooded hope, will blink through steely blue eyes before the end.