[samlevine]

>Climate change is a great example of a wicked problem: Quick, somebody tell me what the acceptable maximum amount of CO2 in the atmosphere should be, in parts-per-milion! Provide me with the answer to that question, and you win a pony!

We don't know. At some point 450ppm was considered acceptable, but at this point the maximum acceptable level may well be 350ppm (pre-industrial revolution it was around 275ppm).

Right now we're at around 390ppm, so whatever it ends up being we have to reduce emissions from their current levels on at least a per-capita basis if not overall.

[fraserharris]

"We don't know" is the answer he is looking for to his rhetorical question. It's a value judgement. The island nations that are losing land to rising oceans have a very different idea of what is acceptable to northern nations enjoying longer growing seasons and milder weather.

[InclinedPlane]

The point is that we don't know. And it'll take literally trillions of dollars of effort to change our CO2 output substantially, so it's a bit of a sticky situation.