I was a little surprised to discover that there are 43 million more people in the USA in 2010 than there were in 1997. 3.3 million more people per year is non-trivial. It seems to me that the people who are most concerned about the environment should be more militantly anti-immigration than anyone. And yet, you can pretty much count on a rabid tree-hugger to be enthusiastic about the ongoing third-world migration.