I am skeptical that more terms in equations can quantify the effect of losing, e.g. biodiversity. Markets have shown time and again they cannot effectively price long-term risks, and people are irrational and unable to account for costs that are farther in the future than their own lifetime.

The post you’re responding to says “people are irrational and unable to account for costs that are farther in the future,” not “I don’t care about costs that are farther in the future than my own lifetime.”

It's fuzzy, but that doesn't make it invalid.

Consider that a ban on cutting 'old growth forests' is really just a 100% tax in market terms.

Carbon taxes can be calculated to have a specific effect, though the impact of the revenue itself on green R&D etc. is impossible to really measure.

I respectfully disagree. It's not just fuzzy, it's completely wrong. Imagine 200 years ago asking an economist to estimate the cost of destroying 100kg of pure Uranium 235. They simply did not understand its value, not only because it could not be utilized with current technology, they did not even understand what technology could utilize it. Worse, if they understood radioactivity, which they didn't, they might consider it to have negative value, because U235 is highly radioactive and will absolutely give you acute radiation poisoning. However, today that amount of nuclear fuel would be worth millions, if not billions of dollars.

We have the same situation, but not with materials for consumption, but the natural world, in particular, rainforests. In 200 years we might actually have half a chance of understanding what we're destroying in 2020.