I've written on demographics before (here related to environment and here related to transportation infrastructure). Many articles I see associated with low fertility in countries like Italy and Japan focus on how that is a problem because of how it strains their economic structure. Other demographic articles that deal with environment focus on how our large and growing population has overstrained our planet. Agreed.
What this article points out is fertility rates are dropping amazingly fast in many countries. For instance from 1984 to 2006 it dropped from 7 to 1.9 in Iran. They accurately use the word "astonishing" to describe that. Fertility rates are anchored in social norms, so it's difficult to imagine social trends changing faster than that. In fact, I have a difficult time imagine them changing that fast period.
I am going to quote the last three paragraphs from the story directly, because it articulates our position here on the earth better than I ever could:
"In principle, there are three ways of limiting human environmental impacts: through population policy, technology and governance. The first of those does not offer much scope. Population growth is already slowing almost as fast as it naturally could. Easier access to family planning, especially in Africa, could probably lower its expected peak from around 9 billion to perhaps 8.5 billion. Only Chinese-style coercion would bring it down much below that; and forcing poor people to have fewer children than they want because the rich consume too many of the world’s resources would be immoral.
If population policy can do little more to alleviate environmental damage, then the human race will have to rely on technology and governance to shift the world’s economy towards cleaner growth. Mankind needs to develop more and cheaper technologies that can enable people to enjoy the fruits of economic growth without destroying the planet’s natural capital. That’s not going to happen unless governments both use carbon pricing and other policies to encourage investment in those technologies and constrain the damage that economic development does to biodiversity.
Falling fertility may be making poor people’s lives better, but it cannot save the Earth. That lies in our own hands."