[PIF]

“If this thing went off, would global warming still be a serious issue?”

Well it might, if there were any surviving humans to make the observation. The handful of survivers would most likely be more concerned with finding something to eat and clean fresh water.

The explosion would be so huge and likely of such duration that within one year NA would be a dead zone, and a few years after that the rest of the world would be effected, including the southern hemisphere.

[ROLF of the HILL COUNTRY]

The reports I've seen say it would certainly be bad for the Midwest and New England, but NOT the entire continent! Europe and the rest of the world will have spectacular sunsets and cool summers for a few years.

IOW, something more on the scale of a couple of Krakatoas, than permanent harm. (Except for those in the immediate vicinity and the aforementioned US zones, of course; it'll be a bitch for them!)

[uncbob]

Exactly— It could be how civilization goes the way of the dinosaurs