Tons of environmental issues are directly related to overpopulation--habitat destruction, global warming, plastic in the oceans, etc., all scale with the number of people. They also scale with other things (like economic affluence and specific policies and industries), but saying that they're "not related" is utterly wrong.

It doesn't look like we're on target for an Erlich-style catastrophe--that has, thankfully, turned out to be a myth (though based on something that nobody realized at the time)--but the human population is way over carrying capacity even with our highly inequitable distribution of resources.