"If there is to be any hope of avoiding civilization-threatening climate disruption, the U.S. and other nations must act immediately and aggressively on an unprecedented scale. That means moving to emergency footing. War footing. "Hitler is on the march and our survival is at stake" footing. That simply won’t be possible unless a critical mass of people are on board. It’s not the kind of thing you can sneak in incrementally. …
It might seem that, given the extraordinary difficulty of hitting 2 degrees C, we ought to lower our sights a bit and accept that we’re going to hit 4 degrees C. It won’t be ideal, but hitting anything lower than that is just too difficult and expensive.
It’s seductive logic. After all, to hit 4 degrees C we would “only” have to peak global emissions in 2020 and decline thereafter at the relatively leisurely rate (ha ha) of around 3.5 percent per year.
Sadly, even that cold comfort is not available to us. The thing is, if 2 degrees C is extremely dangerous, 4 degrees C is absolutely catastrophic. In fact, according to the latest science, says Anderson, “a 4 degrees C future is incompatible with an organized global community, is likely to be beyond ‘adaptation’, is devastating to the majority of ecosystems, and has a high probability of not being stable.”
Yeeeah. You’ll want to read that sentence again. Then you’ll probably want to pour yourself a stiff drink.
Obviously, “incompatible with an organized global community” is what jumps out, but the last bit, “high probability of not being stable,” is equally if not more important. One of the most uncertain areas of climate science today has to do with feedbacks — processes caused by climate change that in turn accelerate (or decelerate) climate change. For instance, heat can melt the Arctic permafrost, which releases methane, which accelerates climate change, which melts more permafrost, etc.
Based on current scientific understanding, positive climate feedbacks — the ones that accelerate the process — considerably outweigh negative feedbacks. At some level of temperature rise, some of those positive feedbacks are likely to become self-reinforcing and effectively unstoppable, no matter how much emissions are cut. These are the “tipping points” you hear so much about.
But at what level? Will hitting 2 degrees C trigger runaway positive feedbacks? It’s difficult to know; this is one of the most uncertain areas of climate science. James Hansen thinks 2 degrees C will do it. Others disagree.
But the situation becomes considerably clearer around 4 degrees C. At that level, there’s good reason to believe that some positive feedbacks will become self-reinforcing. In other words, 4 degrees C would very likely be a way station on the road to much higher temperatures.
That makes the notion of “adapting” to 4 degrees C a bit of a farce. Infrastructure decisions involve big money and long time horizons. By the time we’ve built (or rebuilt) infrastructure suited to 4 degrees C, it will be 5 degrees C [9 degrees F]. And so on. A climate in which conditions are changing that fast just isn’t suitable for stable human civilization (or for the continued existence of a majority of the planet’s species).
Oh, and by the way: According to the International Energy Agency, we’re currently on course for 6 degrees C [10.8 degrees F]. That is, beyond any reasonable doubt, game over.
So this is where we’re at: stuck between temperatures we can’t possibly accommodate and carbon reduction pathways we can’t possibly achieve. A rock and a hard place. Scylla and Charybdis.”