Upvoted for the thoughtfulness and references! That said:

> We're talking about real ecosystems and their incalculable impact (there are estimates of the economic importance of reefs, but it is the scientific and social impacts which are incalculable) on real people, alive today, living right now, that should be alarming and upsetting enough without considering long-term geological scale issues.

My point isn't that people shouldn't be upset. My point is that it's important to spend one's upset wisely, not to exhaust it on things which don't matter as much.

And frankly, considering evolutionary timescales doesn't automatically make everything better -- it just puts things in perspective. Yes, a world without Polar Bears would be a worse world. But considering the bigger picture, we're already living in a worse world. I'm already pissed off about what we did to all the other hominids, and the Mammoths, and the Woolly Rhinoceroses, and the Glyptodonts, and the Sabre-Toothed Cats, and the giant Sloths, and the giant Lemurs, and the Aurochs, and the Elephant Birds, and the Sea Cows, etc. etc. etc... The world was once a more wondrous place, and we butchered it. Adding Polar Bears to that list will absolutely upset me further -- but, as the record shows, like it or not, life will go on.

I don't say this to be cavalier. I say this because it's important to be able to distinguish "life will go on" scenarios from "life won't go on" scenarios. Those are also something we can see in the geological record, and are worth taking very damn seriously. If we lose Polar Bears (or coral reefs, or other charismatic indicators which people tend to focus on), life will go on. If we lose plankton, it won't. If we focus our upset and our policy-making on the former -- at the expense of the latter -- then we're potentially in very serious trouble.

>> Fact is, a lot of the rest of the chaos that is predicted from climate change is, on a long baseline, a more or less normal state of affairs.

> This statement is actually most inaccurate when it comes to the current rate of climate change. There are multiple studies, and levels of evidence, at multiple geological time scales, which show that the current and predicted rates of warming are unprecedented throughout geological time. The current rate of warming is faster now than at any time in the last 11,000 years [1],

True, but this is cherry-picking the data. Extend that window to 15,000 years, and it is no longer even close to true.

> and it may occur faster than any climate change which has occurred in the last 65 million years [2],

Yeah... um, sorry, that's a load of bunk. First of all, they're not talking about what's happening today, they're talking about the worst-case end-of-century 6c models, which rely on scenarios in which population growth doesn't slow down and solar panels don't get cheap. Even considering this, saying that this will be "10x worse than any climate change of the past 65 million years" would require being pretty wildly ignorant of what's happened in the past 65 million years. During Meltwater Pulse 1A (14.6k years ago), sea levels were rising at 50-100cm per decade. Not even the worst-case 6c models predict anything like that. And during the Zanclean flood (5.33M years ago), sea levels were falling at 50-100cm per month (unless you were in the Mediterranean, in which case they were rising at 20-40cm per hour). So, really: we're heading towards a climate event which is 10x more dramatic than that? My ass. Absolute ignorant rubbish.

> current rates of warming are substantially faster than that at the end of an ice age [3], and CO2 levels are currently higher than at any point within the last 800,000 years [4].

Yeah, and that last point is something to be genuinely worried about. As is the fact that we're on track to take C02 on a multi-million-year excursion, at least. We're taking the climate outside the envelope in which our species evolved... and, yes, that should be very disconcerting. We certainly should stop doing that. But whatever we do, we should absolutely make sure that we don't lose the plankton. That's got to be a higher priority than pretty much anything else.

This why I find the consideration of deep-historical and evolutionary and geological timescales useful: not to tell us that we shouldn't be worried, but to better inform us as to what, exactly, we should be worried about. What they tell us is that, on a timescale of decades, the large-scale migration and resettlement of human populations is not only survivable, but thrivable. It will be profoundly disconcerting to many people, but we did it once in the 20th century, and can do it again. It is not an existential threat to civilisation, the way it is often portrayed. Similarly, the consideration of deep time tells us that the loss of apex species and the fragmentation of ecosystems due to a rapidly-changing environment is, again, bloody disconcerting, but not an existential threat to our planet.

So we should take all of the above issues seriously, but not more seriously than something which is an existential threat to civilisation and the planet. Ocean Acidification is potentially such a threat. A future in which we save the Polar bears, save the coral reefs, save the coastal cities -- and lose the plankton -- is no future at all. That's game over for absolutely everyone. Our priorities should reflect this fact.