Climate change will either destroy the planet, or some team of scientists and engineers will avert disaster by inventing carbon capture or whatever. It is highly likely those scientists will have been born and raised in a well educated middle class family somewhere in the developed world.
I too have heard this from people. But when I do, I can't tell if it is the root cause or a rationalization. There is still intense social pressure to have children, although I certainly remember it dropping over the last 25 years. Having children is still the assumption for a heterosexual couple, and you are often expected to provide a rationale for why not, and you feel you will be perceived negatively if the rationale is seen as selfish, and people who do choose to have children still sometimes take your choices as a criticism about their life choices. So you come up with some banal reason to deflect the conversation you have had too many times already. Or a reason to justify the decision to yourself, because social pressures are telling you it is a selfish decision and that selfish decisions about your own life are somehow bad.
Anecdotally: I've had multiple discussions with employed, unburdened men and women (particularly women) in their mid 20s who have decided not to have children for one reason: Climate change.
The planet is collapsing. Our children are likely to die of hunger, disease, or warfare as things become more destabilized over the next 50 years.
We don't believe their lives will be better than ours, and we don't want to further deplete humanity's scant resources.
From this perspective, having children is selfish.