I guess that by runaway, you mean completion of a positive feedback loop like the 4 tipping points. Many think that the open ocean tipping point is passed and will lead to tundra and oceanic methane self release, followed by CO2 release.
I certainly hope we have time to prevent the other tipping points from being completed.
Once something can not be changed by human action and is basically controlled by the laws of nature, it is in 'runaway'. When we look at sequestered carbon, this has been less in past thermal max episodes of PETM (30% ELE 30MY recovery)and the Permian Great Dying(95% ELE and 50MY recovery). Then it also apparently did not release all the sequestered carbon but stopped at less. Estimated 70% from some(Permian, PETM less).
This 'episode' could do the same. Still not a rosy thought.
Runaway to 100% or some point below is probably the runaway called 'the Venus Effect'.
Baked and boiled to no life possible. Ever.
Or a worse than Permian ELE, with recovery in the many millions of years.
Recovery from AGW in 400 years if people reduce emissions enough in time. Somehow, some way, natural, artificial, or Divine. I guess many of us will see it first hand, whatever happens.
As reported before, previous hyper-thermals(not thermal maxes) stopped short of runaway at 1.5* C warming (global heat average). Do not depend on the IPCC or wiki.
"2014 was one of the warmest years on record for America’s wintriest state. It was also the warmest for the Bering Sea and Anchorage’s warmest since 1926. In fact, for the first time in recorded history, the temperature never dropped below zero in Anchorage for a whole calendar year.
So with skis stuck in closets and White Christmas dreams dashed (see video above), Alaskans have more reason than ever to pay attention to climate change. From the LA Times:
“To me, the fact that Anchorage won’t dip below zero degrees in calendar year 2014 is just one more signal — as if we needed another one — of a rapidly changing climate,” said Andrew Hartsig, director of the Ocean Conservancy’s Arctic program.
Hartsig said Anchorage’s comparatively balmy weather is consistent with other long-term trends, including diminishing summer sea ice and increasing sea surface temperatures.
“These are definitely red flags that are very consistent with climate change,” said Chris Krenz, senior scientist at Oceana, an international conservation group. “These are anomalies … that show our climate system is off-kilter.”"http://grist.org/news/anchorage-alaska- ... gn=climate