[hirundo]

And do microscopic and subsurface diversity count? If they do the proportion of anthropogenic diversity decline might look a lot smaller. Or do we only care about visible flora and fauna for this purpose?

Human pollution creates new niches that didn't exist before. Microbes in particular can adapt to them in dramatic ways, increasing genetic diversity. Surely we don't want to promote diversity by finding novel ways to pollute. Biodiversity can increase as a sick ecosystem decays, so sustainability is a crucial consideration. Below some threshold more radiation increases biodiversity. But is it worth more mutant babies?

So changes in absolute quantities of biodiversity might not be a good way to measure the health of the environment. Optimal biodiversity probably depends on for who, and is different each species and niche.

[exporectomy]

Perhaps not because microscopic organisms can re-evolve faster.