@cd: The average range of estimates is 2 to 4 C warmer than some time in the past. (Bold mine)
The Summary for Policy Makers at the beginning of AR5 defines “the past” by referencing temperatures to the global mean surface temperature averaged over 1985-2005. According to WoodForTrees, the 20 years 1985-2005 averaged 0.273 °C above HadCRUT4’s reference point.
Using “today” it is closer to 0.8 to 2.5 C.
If you take “today” to be the ten years 2005-2015, those averaged 0.493 above the HadCRUT4 reference point, an increase of 0.22 °C over “the past”, while the 20 years 1995-2015 averaged 0.443 above it, an increase of 0.17 °C. That would decrease my 2-4 range to about 1.8-3.8, considerably more than 0.8-2.5.
However my 2-4 range was a bit simplistic. The projections depend among other things on what CO2 does. As I was saying earlier, according to Hofmann et al the excess of CO2 over 280 ppmv during the previous millennium has been very well modeled as having a constant CAGR of 2.155% and reaching 120 ppmv (as the excess over 280) in 2015. If that keeps up, the result during this century will be essentially the red curve labeled RCP8.5 (Representative Concentration Pathway) in this plot:
The surface’s response to this additional CO2 depends on many other unknowns besides CO2. By varying those unknowns a climate model will generate a range or ensemble of temperatures. And different models may project different outcomes even under the same assumptions, due to the variety of “equally plausible numerical representations, solutions and approximations for modelling the climate system, given the limitations in computing and observations” [AR5, FAQ 12.1, p.1036]. Taking all this into account, the most likely outcomes of RCP8.5 up to 2100 are projected by the red range in Figure SPM.7(a) on p.21 of WG1AR5:
Taking “today” to be about 0.2 °C as above, i.e. subtracting 0.2 from what Figure SPM.7(a) shows, the further increase for 2100 assuming RCP8.5 is 2.6-5.2 °C. For the much lower RCP2.6 (the green curve in my first figure) the corresponding range is 0-1.5 °C.