There's an interesting podcast with ethicist Travis Rieder (ht: Daily Nous) discussing the ethics of having kids in light of climate change. Rieder suggests that it's morally problematic to have children at all, and probably out of bounds to have more than one, given the immense "carbon footprint" of the decision (especially in the US). This one decision, after all, can be expected to make more of a difference than everything else in your life combined (especially once you build in the likelihood that your child will themselves, at some point down the line, have further children of their own). At one point they mention estimates that a lifetime of recycling saves 19 tons (iirc) of CO2-equivalent, whereas the long-term legacy of reproducing is estimated at 9000 tons.
In line with my previous post on the topic, there are two main points I'd like to highlight in response.
1) Given that you can offset carbon for around $1 per ton, these numbers are actually relatively trivial. The average American is responsible for around 20 tons of carbon emissions per year. In light of this, it seems completely ridiculous to suggest that people mustn't have children, when they could instead do just as much good by committing to donate at least $20 per year, per child, to Cool Earth or similarly effective environmental charities. That is a much less onerous moral ask!
Even if you go with the high-end estimate of 9000 tons (which I gather is meant to cover the long-term "carbon legacy" of reproducing), I bet a lot of would-be parents would much rather pay a one-off $9000 "environmental impact child license fee" than refrain from procreating. So again, it just seems like bad moral advice to insist on the latter.
(2) As further explored in my previous post, this completely neglects all the positive effects your child will have on others throughout their lifetime (and your children's children's lifetimes, etc.). If you raise your child to more than offset their carbon footprint (which, again, just costs $20 per year), their existence could be positive for the climate -- a positive effect which, like the previously assumed harms, gets amplified over time by the "legacy effect" of in turn influencing their children, and so forth. (And that's not even getting into the non-environmental benefits discussed previously.)
And this isn't just idle speculation of a "well, somebody could choose this..." form. If we focus our attention just on those who would otherwise be convinced to refrain from having children for environmental/moral reasons, we're talking about a highly morally/environmentally motivated audience. If they were willing to refrain from having their desired number of children just for moral-environmental reasons, they'd surely be willing to instead donate a few dollars a year to achieve the same environmental goals. And they're likely to raise their kids to share these values. (One can never be sure how one's kids will turn out, of course, but I assume there's at least a decent correlation between the values they're raised with and the values that they end up accepting and living by in future.)
So again, given how easy it is to make a huge difference with a small donation, I just find it baffling that ethicists even talk about -- let alone categorically recommend -- such unnecessarily drastic sorts of measures.