Are we now in a runaway climate change regime, where zero further human impact on the environment will not prevent change to the equilibrium state of the Earth's atmosphere?
Runaway climate change is, given our current state of knowledge, only something that could be confirmed in historic context - in the rear-view mirror. Inconveniently, there's likely to be a much-diminished version of human civilisation around to observe it, if and when it does happen.
In other words, it's too early to tell if we've passed a catastrophic tipping point.
We don't know what the equilibrium state of the Earth's atmosphere is. It will take 30 years for our current stock of GHG emissions to fully show its effects: and we'll be continuing to release GHGs for a while, so the equilibrium will continue to change.
But it's worth bearing in mind what we can do, when we really have to; World War II saw massive realignments both in industrial production and in expectations within a very short space of time: after decades of delay, it now seems likely that decarbonisation will require at least a similarly fast and large industrial realignment; and it is possible.
We might have some wiggle room, or might be past the tipping point, but we do not have enough info to be sure. It depends of unknown strength of known positive feedback loops, like:
- melting permafrost releasing potent greenhouse gas methane
- drying permafrost bogs release CO2 or even burn
- warming ocean might release https://en.wikipedia.org/wiki/Methane_clathrate (methane ice) - remember Deepwater Horizon?
- and likely more.
What we are certain is, the more CO2 we release, the closer we will get to the tipping point, after which different climate might stabilize, close to PETM, the onset of which has been linked to an initial 5 °C temperature rise and extreme changes in Earth’s carbon cycle. It lasted about 170K years. Alligators in Alaska, ocean level 270 feet (90 m) higher), lots of arable land and many big cities (London, New York, Shanghai) submerged, etc.
How big human population such different planet can support? We don't know, but I am not sure we should try to find out the hard way.
Or another way to formulate this: Can Earth support intelligent life? We don't know, we are about to find out.
One solution for Fermi Paradox ("Where is everybody?") is that technological civilizations like ours destroy their environment and go extinct.
According to satellite datasets (RSS), last year was not even close to being warmest ever. The warmest year still is 1998, and the second warmest is 2010.
It is beyond me why NOAA or NASA GISS (who use NOAA's data), ignore satellite measured temperatures, which give far more accurate and complete picture of the world's global temperature.
Below is a map of the coverage of the data NOAA and NASA GISS uses. I find it hard to believe they can tell us the global temperature in sufficent accuracy to claim whether some individual year was some hundredths of degrees warmer than some other.
There are almost no data on the oceans, Antarctis, Africa or the north pole. Just extrapolating the little data they have over thousands of kilometers just isn't going to produce accurate enough data to detect such a small changes.
This in mind, I'd rather turn to the satellites, which show nothing to be worried about.