Overpopulation, it the scourge of our planet in any event.
Oddly enough, you have found a subject on which we can agree, at least in principle.
Anthropogenic Climate Change might or might not be real. (Climate Change - without regard to cause - IS real.) But pollution in impoverished countries is due to having too many people who burn things in open fires for heat, who destroy trees because they don't have more efficient ways to obtain fuel and building materials.
Our scientific and industrial renaissance over the last few centuries enabled us to be more efficient, which helped exacerbate the problem of increasing population leading to increasing resource consumption leading to more waste by-products. Part of the medical issues we have now - including rising health care costs - stems from supply vs. demand issues. Too many people need health care but the illegal immigrant influx only increases the local demand without increasing the supply side of that situation any better.
When researching my family history through that popular ancestry site, I found many cases, one might even say innumerable cases, where at least two or three family members died before reaching adulthood. Many of my pre-Cilvil War families had over a dozen children but a lot fewer who lived to adulthood. At least five isolated cases stood out where one of my "nth" cousins died at an age less than one year old. That frequency of early death didn't match up to ongoing war but rather correlated to people in rural areas away from any place with a higher proportion of medical care availability.
In a way it is part of survival of the fittest, but nature maintained balance over the long term by making the weakest members due of disease, age, or predation such that species populations would stay in balance over several generations. If a group of predators died out, their prey had a sudden population growth, which fed the dwindling predator population, causing THAT to increase, which in turn led to the NEXT generation of prey being brought back into balance. Drought, flood, and famine did their share of population control. But now... the extreme weather being felt around the USA would normally have taken care of population extremes - but not now. One might say that thanks to the Renaissance, we have sown the seeds of our own over-population doom.
Right now, mainland China is actually suffering a population decrease for reasons far too complex to examine here. (Besides, I've got stuff to do this morning to help my wife.) India is now the most populous nation on Earth. China's anti-family policies from the last two generations finally took their toll... a toll that might lead to serious diminution of China's economic and industrial strength as they find they don't have enough workers to pay taxes to support their rapidly retiring older generation.