There are multiple people on my Twitter timeline mentioning the fact that CO2 levels have passed 400 ppM for the first time. Let’s just point to this well informed and interesting explanation by Peter Gleick on Scienceblogs, titled “The Last Time Atmospheric CO2 was at 400 parts per Million Humans Didn’t Exist“.
As Gleick explains, 400 ppM means an ice-free Arctic, average temperatures up between 3 and 4 degrees Celsius, and over 10 degrees at the poles, sea levels between 5 and 40 meters higher.
So why do I think this is irrelevant?
The answer is easy.
Anyone paying attention knew a long time ago that we will reach 400 and blow right past it. The fine people at 350.org want humanity to keep CO2 levels under 350. That is not likely to happen any time soon.
To explain this with a little comparison to bitcoin prices, it didn’t matter much if the price was at $2 or at $5 some time in 2011. It was always sure to go way up anyway (it is around $110 now).
The one thing that matters most is if humanity somehow will be able to avoid the positive feedback spiral leading to Venus syndrome. This question has only two possible answers.
In contrast, assuming stabilizing at some level or other of global warming, that is a question of degree. While much would change, there would still be at least some life left on the planet, possibly even human life.
For all of that, blasting through 400 ppM is not ever so important. The real fight will come in the next couple of decades.