Start talking about the "elephant in the room". Overpopulation is almost never mentioned in discussions about the environment.
There seems to be a taboo against directly addressing the simple fact that each human on this planet has some negative environmental impact. So do other animals, and some plants, but few of them are supported by the complex industrial, chemical, and resource-depleting lifestyles we have come to depend upon.
Politicians are unwilling to touch the subject, for fear of losing votes. Religious leaders want to expand their memberships, and are ignoring the inhumanity of the continued growth of population on the wellfare of future genereations.
Economists largely see more people as more labor, or consumer market, thus money is their concern, and they have a peculiar tendency to ignore any environmental consequence.
Scientists feel it is only their technical ideas they should offer, and never put forth the simple observation that ultimately, if population continues to grow, the best science can only be a temporary, partial solution to environmental decline.
Military leaders want more personnel, stronger armies.
It seems abundantly obvious that if a small percentage of the efforts of all these "leaders" went into developing a sense of personal responsibility to have small families, and to promote this behavior in others, the problem would solve itself.