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Why do so many people believe this notion that current trends of warming imply looming mass extinction? What is the argument or evidence for this?

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As others have explained, there is the unprecedented loss of diversity of species and change in climate. I’d add that there’s also no evidence this will slow or stop (at least that I’m aware of), but there is mounting evidence that it will continue and even accelerate (which we are possibly even witnessing today).

The loss[1] of diversity is primarily due to the way we abuse the ocean - bottom dredging of shellfish beds destroying whole slow-growing ecosystems, dumping sediments, toxins and excessive nutrients (which amount to toxins) in the ocean via runoff from land, indiscriminately catching whole populations of free-swimming fish, and so on.

Climate change is just the cherry on top, really, compared to our other efforts to reduce biodiversity.

1. I don't know why we use the word "loss", which implies an accidental outcome, when we're systematically setting out to plunder and strip-mine ecosystems.

Do you know if diversity collapses in the ocean is more severe than on land? I know vast deforestation and destruction of the water cycle (either by reduction or degrading via pollution) has a virtually incalculable impact on this, but perhaps in the ocean it’s even worse.

Warm water can’t solve as much oxygen, plus there are plenty of self-reinforcing effects that might have already started happening.

Life won’t die, we had plenty of mass extinction, but most of current species do like their oxygen. Also, their shells.

But there's also plenty of negative feedback processes. Why assume there'll be extreme runaway apocalypse from the warming.

Why assume there won't be? Seems like the risk there is greater.

What’s runaway is our rate of change in releasing co2, compounding annually at something like 1-2%

There's negative and positive feedback processes. On balance the positive feedback processes outweigh the negative ones. e.g.

* Melting ice caps mean more heat absorption

* melting permafrost releases methane

* Warming oceans freeze frozen methane

I'm forgetting a bunch, doing this from memory. What negative feedbacks do you believe outweigh these?

The mass extinction isn't looming. We're in the middle of it right now.

The current mass extinction doesn’t have much to do with the climate crisis though, it’s caused by good old fashioned massive exploration of the environment for human gain. (This is, of course, not a good thing. It’s an already massively fucked with ecosystem that climate change is causing increasing strain in)

> Habitat destruction is the leading cause of biodiversity loss.

https://en.m.wikipedia.org/wiki/Habitat_destruction

> Why do so many people believe this notion that current trends of warming imply looming mass extinction? What is the argument or evidence for this?

A truck filled with ecological research

The velocity of change is historically unprecedented and we have a good amount of empirical evidence of what it takes to collapse ocean ecosystems.

historically unprecedented

Unprecedented in the last 100 years, million years, or 500 million years? That's a lot of precedent with some major and rapid climate changes.

Are you aware of the climate and antmosphere ever changing so abruptly according to ice core records?

Ice core records don’t go back that far. But some past mass extinction events were believed to be caused by more rapid climate swings resulting from asteroid impacts etc.

The thing about our situation is that no asteroid strikes or major geological events have occurred. So we know it’s possible to have major swings, but it’s less clear that they should occur without some obvious trigger.

What resolution does ice core records have? Do they really show year-over-year change or are the core records being smoothed through natural processes?

Great questions, and I don’t have the answers. I’ll definitely look into it though.

I read a book about this once, forget the title. Greenland’s cores have clear annual layers for several thousands of years (validated by extra ash layers from known volcanic eruptions), and they can measure carbon and temperature from the isotopes trapped inside (temp is measured due to some effect of oxygen isotopes following a reliable temperature gradient or something like that, they had a couple independent measurement methods that matched up). At some point the compacted layers start to merge but they can still reliably estimate because the overall cyclic trends (on multi thousand year scales, due to mathematically regular wobbling of earth’s rotation and other factors) follow the same trends from the clearly annual layers. This goes back several hundred thousand years, with temp increases always following carbon increases.

Edit: the book was The White Planet by Jean Jouzel, Claude Lorius, and Dominique Raynard

Pre-history usually refers to a time period approximately up to the invention of writing, so some several thousand years. If your time scale is the past 500 million years, there have been some real big mass extinctions to go along with those rapid climate changes. Not sure that's an encouraging precedent.

The climate has rapidly changed throughout Earth's history. Our current period of warming over the past couple of centuries began at the end of a mini ice age, so its not surprising temperatures rise when exiting the ice age. Just like its not surprising that temperatures rise after winter into spring & summer. CO2 is more likely a side effect of warming, coming from the warming ocean, than it is the driver of the warming.

This is just badly wrong and ignorant. Ask anyone who's actually studied the interglatial periods - in other words, the scientists who've provided the temperature information you're referring to - and they'll tell you why you're wrong.

Unprecedented in the era of human farming is sufficient enough for my worry. Yes, life as a whole probably survives whatever happens in one form or another. But those rapid climate changes tend towards seriously limiting the resources available to species living through them. Modern civilization relies on keeping things in a situation where it’s possible to grow enough food to feed 7+ billion people, and I’d rather we not create our own mass environmental change that has a serious possibility to disrupt said food making process.

We’ve been collapsing ocean ecosystems simply through fishing.

200 million tonnes of seafood per year is an unprecedented and unsustainable change. Global warming will of course make things worse but it’s not like the oceans are currently healthy.

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