Bullshit. The shrinkage is a good thing for the planet, because human overpopulation is causing all kinds of problems. The current 7+ billion population is about 3 times the sustainable maximum. Less would be better. For most of history, the population was under 1 million and only crossed 1 billion around 1800. Devastation rose sharply after that, so I'd call 1 billion a tolerable maximum and 1 million a lot better for everything else on the planet.
Yes, a shrinking population poses its own problems. However, these are much less than the cost of an environmental crash, like we're heading for now. Infinite growth in a finite system is the philosophy of the cancer cell, and that ends badly for everyone.