>as well as dramatically limiting immigration (accepting migrants only from other highly developed countries, deporting all illegal immigrants, and ceasing all permanent refugee programs) in order to limit overall population growth.
Those people won't cease to exist. They'll just stay in poorer nations. In fact, wouldn't accepting them into a wealthy nation reduce the average number of children they have? And if these nations can drastically reduce the impact of their citizens, all the more reason to start recruiting migrants.
The reduced number of potential children is offset by the significantly higher net increase in emissions from moving from a poor country to a rich country, and participating in a more CO2-intensive economy.
Unskilled migrants and refugees move to the West for economic reasons. However, their labor can increasingly be replaced with robots. Additionally, in Welfare states, their existence is a cost on the rest of society, as well as increasing demand for finite land and transport infrastructure, thus worsening quality of life for existing citizens.
With all of that, it would be much more effective to provide free and universal education, contraception, and abortion for women, which will also address the underlying cause of mass migration and habitat destruction - regional human overpopulation.
Those people won't cease to exist. They'll just stay in poorer nations. In fact, wouldn't accepting them into a wealthy nation reduce the average number of children they have? And if these nations can drastically reduce the impact of their citizens, all the more reason to start recruiting migrants.