by 2100. the output of at about 525 million people. when the other hand, if we reduced immigration -- >> tucker: weight, stop your out there. we are on track to add, to be at 500 million by the end of one? how long >> by 2100. >> tucker: by the end of this entry? >> by the end of the century. most of this population growth is driven by immigration. if you get to play cut back to the levels of immigration we had 50 years ago, we do be untracked to stabilize our population in a few decades. basically what happened the american people have chosen to stabilize our population, having about enough children to replace ourselves. but congress has increased immigration in recent decades and so we are on track to add hundreds of millions more people. that has a pretty large environmental impact. whether you talk about greenhouse gases, sprawl, loss