A large band around the equator will become unsurvivable. Hundreds of millions of people will flee to cooler climates. Countries will already be straining to provide food and water for their people. This will lead to wars for resources. Nations with nuclear capabilities will fracture and collapse, leaving their weapons in the hands of warlords and despots. Pandemics like COVID will become increasingly more common, not just for humans but for our livestock and crops. I hope you are right, but then again 5 billion might be a conservative estimate.