This would mean that there would be a single effective heat capacity for the climate system, and a single effective time constant for the system as well. (realclimate.org)
It also seems to rely on a certain value for the «effective heat capacity of the oceans»: (realclimate.org)
The study also contains a cautionary note: if effective heat capacity should prove to be less than estimated in the study, or the carbon dioxide degassing timescale proved longer, it could result in temperature overshoots in which initial temperature decreases are reversed when carbon dioxide re-accumulates in the atmosphere. (ceassessment.org)