[ppf]

That's not very humble. His assertions are quite basic, and don't need research-grade qualifications to consider. The earth has certainly prehistorically been much warmer, so nature handled it just fine, and it is an interesting question to consider how much more arable land a warmer earth would have.

[Sharlin]

Earth has not been considerably warmer prehistorically (a term that, technically speaking, refers to the period between the appearance of tool-using hominins and the invention of written history). If you mean paleontological periods before the appearance of genus Homo, yes, but that's not very relevant given how the GP talked about the human civilization (which, incidentally, did not exist in the prehistoric era either!)

As far as we know, the loss of arable land caused by the climate change (and other anthropogenic environmental changes) far outweighs possible gains elsewhere, and even if it didn't, agricultural land area is not exactly fungible.

[ppf]

Ok, I used the wrong word. I was also referring to OP's point that "nature was just fine" - the earth has been up to 12degC warmer than present, before humans could make any impact. My point is that, taken in isolation, a warmer earth is not fundamentally bad, nor new.

As for his point about humans preferring warmer temperatures - hopefully that is self-evident.

>As far as we know, the loss of arable land caused by the climate change (and other anthropogenic environmental changes) far outweighs possible gains elsewhere

Would like to see an analysis of arable land gained vs. lost. This is all purely hypothetical, of course - such a change would be drastic, and as you point out, arable land isn't exactly fungible.

[NeedMoreTea]

A warmer earth with humans on it is fundamentally new, as we've not been around that long. Even forerunner species like Homo habilis only go back three million years. An eye blink in the geologic record, and long, long after the five mass extinctions.

12C warmer would put vast amounts of the land area of the planet outside habitable conditions for humanity. We'd probably be restricted to former arctic regions, and not much else. So no, I don't think it's self evident at all. It won't take many degrees rise to rule us out of equatorial regions, then tropical...

[ppf]

True, it would be new to humans, but (at least initially) it's not fundamentally a problem (please note, I'm arguing in the most theoretical sense here). Large amounts of the equatorial regions are already uninhabitable - it would be interesting to see an analysis of the total inhabitable land loss vs gain for each degree in temperature rise.

[NeedMoreTea]

Given a slow enough rate of change, species would adapt and migrate. Presuming there aren't farms, cities, roads, railways, dams and fences preventing smooth migration to the newly appropriate regions.

My concern is we're changing the climate at geologically unprecedented rates, likely far too quickly for species to evolve and migrate, even if we hadn't locked up 50% of the world's landmass for our own use. That will play interesting havoc with food chains no matter what former permafrost and arctic is freed up for use (with its own emissions load on melting).

[ppf]

Fair enough - so how are humans sustainable?

[Sharlin]

And the "hothouse" Earths were drastically different from Earth today. Given time, life adapts, but the point is that there's no time. There have been sudden, drastic global climate changes in Earth's history before. It's just that they have been accompanied by massive extinction events. Whatever we do, we probably won't destroy the whole ecosystem. But that's a rather ridiculously low bar to clear!

[ppf]

Sure, the "hothouse" earths are at the drastic end of the scale, but earth has spent significant periods of time at temperatures a few degrees above current. "There is no time" is a complex assertion that needs at least some research, and if there really isn't, what do you propose we do?

[orbifold]

The details make it a very hard problem. There is scientific consensus that a too rapidly changing climate leads to mass extinction of species (plants, animals, etc.), because suddenly species are not adapted to the climate they find themselves in and can't migrate quickly enough. This loss of biodiversity should be of great concern, because it is irrecoverable. There are tons of other non-obvious problems that are not commonly understood.

[ppf]

It is a very hard problem, which is why I personally hate to see so many issues conflated under one slogan. Your point about species adaption is a fair one, however if we are going to consider absolute effects on biodiversity, direct human activity has already had a significantly worse effect.

[shkkmo]

> if we are going to consider absolute effects on biodiversity, direct human activity has already had a significantly worse effect

Do you have a source for this or are you just basing it on "common sense"

It does toe that Hans have primarily impacted species that tend to sit higher on the food chain. We have caused the extinction of more animals than plants. Rapid warming can kill of plants that can't move quickly migrate quickly enough to stay within the temperature ranges where they can survive.

It isn't just matter of spreading their seeds far enough (like the reforestation of New England), many plants rely on a prexistingnset of conditions created by the the presence of other species to be able to grow. When the required shifts get large enough there simply may not be enough time for those conditions to be established elsewhere before the temperatures in the current areas kills off the species.

Plants species (and animals like coral) serve as a critical component for many other species. It is quite conceivable that rapid global warming will lead to an extinction event that far exceeds anything that humans have managed to date.

Our understanding of ecological systems is still pretty limited and I don't think we can know for sure how bad it will be. I am personally hopeful that we can delevope terraforming techniques to assist with ecosystem relocation that can mitigate some of this.

[ppf]

I don't really have a source on that, although I'm also not aware of any particular species that are known to have been wiped out due to the current climate change. It is, however, fairly obvious that humans have had an enormous impact on pretty much every inhabitable part of the earth. Even without climate change, it's plausible that human activity will ultimately destroy most ecosystems.

>It is quite conceivable that rapid global warming will lead to an extinction event that far exceeds anything that humans have managed to date. >When the required shifts get large enough there simply may not be enough time... >Our understanding of ecological systems is still pretty limited

You've made a number of assertions here about ecology with no reference to research.

This is one of my main issues with the way climate change is presented - much is made of tipping points and the scale of the incoming catastrophe, but the fact is we simply don't know. Even if it is true that we have a low number of decades until irreversible catastrophe, what exactly can be done about that?

[shkkmo]

You are the one who made a strong assertion that the potential for extinction caused by rapid global warming is less than what humans have already caused.

I made relatively few assertions and the ones I did make are basic ecological science. I was pointing out that your strong claim was irresponsible given the plausible possibilities and our limited knowledge.

[ppf]

Not quite. I made the assertion that the ecological damage humans have already caused is much worse than that caused so far by current climate change. We both agree that predicting the further change in climate and its ecological impact is very difficult.

[softwarelimits]

Would you please like to add data and evidence to add some substance to your words? It is not enough to just "say something" on the internet - you need to provide evidence if you want to be taken seriously.

[ppf]

The only assertion I made is that the earth has been much warmer pre-historically, which is a well-known fact and can easily be verified. https://en.wikipedia.org/wiki/Geologic_temperature_record

[gorpovitch]

It is true that the earth has already been warmer. We're reaching points that humans are never seen, though.

Second, the problem here is not only the total temperature variation but the speed at which the temperature is changing.

Think of the difference between a car going from 130 km/h to 0 km/h in 8 seconds, and a car going from 130 km/h to 0 km/h in 0.3 seconds. Not really endearing.

[ppf]

Understood, although we have no way to know if there have ever been similar events, as the geologic record is something of a low-pass filter.

Just for the sake of argument, let's say you find yourself in a car in the second scenario, with no known way to stop it. What would you do? I say this as a pragmatist - if we take the headlines at face value, and we only have ~10 years to avert a catastrophe, then the only realistic way to avert it is if 90% of the world's population spends that 10 years planting trees before killing themselves.

[imtringued]

I'm not sure what the point of suicide is when the worst that can happen as a result of climate change is death.

[ppf]

Right, so what should we do?

[whatawaste]

The earth has also been molten rock at one point too, the issue is can humans survive in that environment, not just the fact the earth is warmer.

[ppf]

The earth isn't going to return to that state any time soon :) I posed it as an open question - given any particular rise in temperature, what is the total loss and gain of inhabitable land?