Second paragraph of third chapter:

But much of the Old City had endured, as had London and Paris, Tokyo, Rome, and major areas of Moscow and Peking—subterranean haunts tucked away in the world's memory like dear, unwanted relations.

I picked this up as one of the few sf novels set in 2021Do Androids Dream of Electric Sheep? and The Children of Men) are better, and also only half of this is set in 2021, the rest being in the year 3000. At the end of the first half of the book, the planet earth disintegrates due to some carelessly wielded new technology. I can say with confidence that this is the most pessimistic of all of the future 2021s I looked at. The rest of the book sees the remnants of humanity zipping between star systems on a converted asteroid, occasionally descending to settled planets to bonk some of the primitives and fight some of the others, and eventually achieve transcendence. The book seems to have a lot of fans who feel it had an important Message. Frankly it seemed to me much the same plot as the Cities in Flight series, with perhaps a little jazzed-up tech (but really only a little). You can get it here.