If mass migration is the solution be honest about it and prepare or send people to places where there is plenty of room to expand and the climate is ok.
However, the climate in Europe, The United States, Russia, Japan, Australia and (LMAO) Israel is ok (as well as holiday destinations such as the Carribean), while all surrounding areas are basically apocalyptic hellscapes that need to be evacuated.

I don't think this migration wave has anything to do with the climate. That was just decided on as the 'scapegoat' for the 2008 economic crash and the failed foreign policy that hit some poor areas of the world hard.
(For example they are trying to sell 'climate' as the cause of molesting Gadaffi and Libya by extension)

Maybe try to make Mexico a better place to live and hold Mexico accountable for I dunno, the fact that everyone who lives there wants to GTFO.
As opposed to hammering on the already outstretched and overcrowded US immigration system. With that said, the US should do more to speed up the process of both taking people to detention centers and sending them back(with enough facilities and resources) as well as legal migration.
The big problem is that the left just wants open borders without any restrictions no matter the consequences and the right doesn't want to spend a single dime on taking care of people who enter a country illegally.