Uninhabitable as in unable to support modern civilization and population levels, probably in large part due to agriculture no longer being viable due to lack of water or weather related issues I'd assume.

That doesn't seem like a good assumption. The fossil record shows a lot of plants growing during previous global warm periods, enough to sustain many herbivores.

Yeah, grass and bushes and trees and shrubs can, have, and will continue to grow in any but the most extreme conditions sure and those are going to be fine for herbivores who can digest and extract nutrients from them, but for the food crops that we can eat, they need pretty specific climates for us to successfully cultivate them at the scale needed to sustain sizable populations.

The temperature isn't as important as the rate of change.

> Also because humans have existed in all sorts of environments from tundras to deserts for tens of thousands of years with stone-aged technology

The abstract perspective of some humans surviving somehow may not be as comforting as you think.

> The abstract perspective of some humans surviving somehow may not be as comforting as you think.

You are right. Humans will likely survive as a species, but not in the numbers and with the comfort we are currently used to.

This is an extremely naive and ascientific hot take.

Dinosaurs are large creatures of a completely different order, not mammals. The sea ecosystem which had evolved over millions of years to deal with those temperatures is a completely different ecosystem from what we have now.

It's not about whether some humans can survive in difficult conditions, it's whether the current ecosystem can survive the unprecedentedly fast and rapid warming. And whether billions of humans will starve

Mammals, reptiles and amphibians existed back then as well, as did a variety of plants. Uninhabitable sounds like most of the Earth turns into Venus, which won't happen. The current ecosystem will undergo change as some species adapt and thrive while others go extinct, migrate or are confined to smaller areas.

What this looks like for civilization and to what extent humans can mitigate is debatable. Climate models aren't civilization models.

There's way too many options to put into even a book, let alone this message[0], but here are some things to consider:

• Burning all the known fossil fuels is more than enough to raise CO2 to the level necessary to severely impact (>25% slowdown) human cognition

• Although plants like CO2, they are often limited by other things instead

• Although we can build personal air supplies for us and greenhouses for plants to optimise each, this is more expensive than not causing the damage in the first place, so not doing the latter implies we will not do the former either

• We've messed up local environments more than once, and observed mass migrations as a result; while I'm fine with migrants and confused by those who aren't, I don't let my utopian ideals blind me to the political reality that this will end badly for many innocent people

• Quite a lot of property and infrastructure at low elevation and near the coast, combined with a significant risk that the threshold for total loss of various major ice sheets[1] is less than or equal to 4 C

[0] written 3h into a post flight cancellation queue for making it the airline's problem that I have work 2000 miles away in 5.5 hours and all the alternative flights they offer are booked out until a week tomorrow, so I apologise for anything weird in this comment

[1] I want to say Greenland, but I don't trust myself in this sleep-deprived state

Climate models might not be civilisation models, but climate has a very large role in the disruption of civilisation models, look at the Sumerians for evidence of climate/regional degradation and the impact that had on their civilisation. And mitigation is only one part of it, when shortages start, it's not just the climate you have to deal with, it's the humans, who are arguably far more vicious and erratic than any weather or climate.

> I find that extremely hard to believe

failed harvests around the world and famines killing millions are an absolute certainty.

Millions yes, but probably livestock first, because a large part of Earth's agricultural production goes into feeding it, not humans directly.

Maybe not. The bulk of livestock are fed with marketed foods, whereas the vulnerable people are subsistence farmers who depend on their own crops.

I would like to make a wager

Would you indeed? I'll take any bet you'd care to place, the San Fernando Valley is sinking feet per year in places due to the volume of water we're pulling out of aquifers right now to support agriculture and the Colorado River doesn't even make it to the Gulf of Mexico anymore for identical reasons. That's the state of play right now at 0 degrees additional warming.

I would like to make a bet specifically targeting the parent comment's absolute certainty that there will be failed harvests that cause the deaths of millions. When do we expect this to happen? How much time would have to pass without it happening to cause you to reconsider the inevitability of this specific prediction?

Ok, $100 USD says that a crop failure resulting in at least 2 million excess deaths happens within the next 20 years, let’s round to <= 31st December, 2042.

Of course by then $100 USD will have the purchasing power of ~$10 USD, so it’s not the riskiest bet on my part.

So these will be starvation deaths? I like looking at excess deaths, so we need to look at the base rate of starvation, and I'd like to go per capita, as I expect population to continue to increase substantially and more people to die of all causes year over year as a result. Can we do $10k?

Most of them will probably have disease as the proximate cause. Dysentery and/or infectious diseases that in well-nourished populations isn't too much of a problem.

Some of them may have armed conflict as the proximate cause. The civil war in Syria had as one of its triggers a prolonged drought with associated crop failures, partly attributed to climate change.

Right, I think we can come up with an agreeable or used an established definition of famine deaths that includes these. I'm taking a closer look at this our world in data page to try to come up with well-defined terms.

https://ourworldindata.org/famines

During the Little Ice Age in Europe there generally was a higher death rate (shorter life expectancy). Food production per capita declined, and while most people didn't outright starve to death they became weaker and more vulnerable to disease.

Given the dual famines in Somalia and Ethiopia right now I expect we should hit the millions dead target within the next 18 months. How long were you thinking we'd have to wait?

Oh yeah I forgot about that, that could do it. Maybe that's where the certainty comes from. My genuine belief is that there will continue be droughts and wars that cause famines and the excess deaths that come with them, but that the overall trend of famine-related deaths per capita will continue to trend downwards despite climate change. I think war and other geopolitical disruptions are the greatest threats to food security.

If you believe famine is going to trend down I encourage you to take a hard look at what percentage of arable land globally is currently in use (we're close to maxed out), how much of that agriculture is dependent upon non-renewable water sources (aquifers), or other water sources that will be impacted by warming. Toss in topsoil depletion, erosion, and desertification. I am fairly certain that a sober look at these things will paint a much grimmer picture of the future.

Yes, this is exactly where I disagree strongly. Malthus and his imitators have all been horribly wrong. I will concede that there is ultimately a finite amount of stuff in the universe, but looking at any apparent hard limits like you suggest has been a recipe for undue pessimism. For example, I don't think "arable land" is a fixed resource.

Anything seems possible when you don't know what you're talking about. There is no spare agricultural capacity to be had anywhere on this planet and the required inputs are both not something we can replace and dwindling.

I know what I'm talking about! I'm talking about how the food ain't gonna run out. If that makes me stupid, then so be it. I'll be stupid and right.

Where are you expecting all of this bonus food to come from? Mars?

And completely different from 'uninhabitable'.

It’s mostly about the rate of change. If we went to where we’re going over a hundred thousand years or even a few thousand, ecosystems could adapt, but we’re digging up and burning hundreds of millions of years of carbon in a century

We aren't dinosaurs. The end of the abnormally cold climate that we (and other mammals) have enjoyed for the past 2.5 million years (aka Quaternary Ice Age) is likely to cause the Earth to become uninhabitable again to us and most land mammals outside the poles (and poles aren't great with their months-long days and nights).

And while this is still unlikely (and we were overdue for a colder, more normal for our Ice Age climate with the end of our interglacial, give or take a few thousand years), we are certainly turning up the heat in an alarming fashion ! (P.S.: the risk comes from the self-reinforcing feedback loops some of which the article describes.)

un-habitable for us, as modern human using technology. We're gonna be fine as a specie. Just not like that.

I think we should welcome it.