On a planetary scale, I don't think we're going to have trouble feeding ourselves, it's just that a) meat is going to become thoroughly unaffordable and b) an awful lot of crop production is going to shift towards the poles, creating many a geopolitical clusterfuck along the way.

Disaster movies are too obvious, and too tidy; it's going to be a century of the average human's life getting just a bit more hellish every year. Acutely hellish for some, barely hellish at all for others, but basically, we're going to slowly roll back most of the improvements in human welfare over the past few centuries until we've got starving serfs all over the place and plagues and famines and natural disasters absolutely flattening entire countries for years at a time.