[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?

[cmendel]

GP's point is that they aren't. We are looking down the barrel of a total ecological collapse, and the trigger has likely already been pulled.

[ppf]

I tend to agree, I was just curious where this discussion would end up. So, what should we do?

[NeedMoreTea]

Start changing behaviour after the IPCC first report came in, in 1990. Waiting until we have not just visible, but dramatic and surprisingly early consequences is leaving taking evasive action in the car until the bodywork has started to crumple. I note that nearly all the surprises seem to be of things being far more or far sooner than predicted...

That leaves dramatic and expensive global scale action. We're not doing it. There's no sign we're thinking about doing it. Let the market resolve is the sole incredibly weak suggestion.

I don't think history is going to view citizens and politicians of the 21st century kindly. I can forgive and understand those contributing to the problem before say 1990, before the awareness was widespread. We've emitted more since 1990 than in the entire time before.

So a planetary scale game of chicken...