There's been an ongoing exchange on the Green Schools list (GRNSCH-L@listserv.brown.edu). In a nutshell, it simplifies to:

Question: Is X a good speaker to bring onto campus for a sustainability presentation?

Answer: He's strongly anti-immigrant. This may not play well with your intended audience:

Amicus curiae: Population is relevant to issues of sustainability. It's hard to reduce emissions when your population is growing. Most US population growth is due to immigration. If we don't stop immigration, we won't be able to get our emissions under control.

While I sympathize with my friend Amicus when it comes to campus-specific emissions (you can't reduce building-generated emissions by adding new buildings; you can't reduce student-generated emissions by growing enrollment), the same doesn't apply on a larger scale. Whether people cross the nation's borders has little effect on global warming. The USA's disproportionate contribution of greenhouse gases isn't due to some influx of fruit-pickers, or chicken-pluckers, or undocumented household help. A migrant agricultural laborer has pretty much the same carbon footprint whether that person is in the US, or Mexico, or Guatemala, or Argentina.

(Ironically, a skilled employee or entrepreneur migrating from Western Europe to the US doubles his/her GHG emissions. Maybe we should impose more controls on high-income immigrants, and let the unskilled in more readily!)

While I'm increasingly convinced that the solution to our sustainability problems lies in more livable communities and more localized economies, neither of those implies or depends on having armed guards at the gate. Smaller colleges have an easier sustainability management task than do multiversities, so limiting campus growth can be a legitimate strategem for a particular institution of higher ed. But nothing in that statement implies that we want to exclude people from getting an education, only that we might want to educate them via an industry with more -- smaller -- participants.

Extend that thinking to the national scale, and you end up recommending more countries, smaller countries. The USA broken up into half a dozen regional republics. Not, I suspect, what your typical "anti-immigrant" demagogue has in mind.

Climate change is a global problem. Part of what eases the way for it is the globalized economy. What will be required to address is will be a global shift in technologies at all levels. Global population control would certainly help, but that's a matter of birth rates, not immigration rates.

Focusing on artificial borders, on human-imposed distinctions without differences, doesn't help us at all.