Many years ago people made a choice. They chose poorly. We survivors live with that choice. The last of the generation that participated in that choice would pass on in a few years. Many of them still deny their culpability. Still.
Those few of us still engaged in academic studies have recently worked out how that poor choice came to be. Humans denied the possibility that we could cause such a change of climate because they believed the world was created perfect and mere humans could not destroy what the Creator had wrought. We now understand humans could.
Our greatest challenge now, though, isn’t growing sufficient crops on the remaining usable land, and it isn’t finding potable fresh water or any of the other dire conditions we face now on the Earth. No, with our now depleted technological capability and lack of infrastructure, we have no way to deflect an inbound comet. In a few months, an ice and rock behemoth now visible to human eyes will erase our mistake just like another did to the dinosaurs.