This is a bad take... Regions affected with mass migration, people without solid infrastructure, AC or clean water, people not able to move are in danger. They are not the ones polluting.
Hypothetically you have 50% less people. Great. Think about who is still there and if pollution really is in decline then.
Problem is we're on our way to reach a point where even if we stopped all our GHG emissions, just the melting of the ice caps and thawing of the permafrost will be enough to create a self sustaining global warming event.
Literally our entire human civilization occurs during a stable climate. If the earth were hotter we'd probably never have reached 8 billion, or if we did it would have been through another way. This is going to be a rough ride, especially for the kids.