The G8 pathway, for its part, is not calibrated to a specific temperature threshold, but is based on the politically influential targets specified in the G8’s 2009 Declaration in the Italian town of L’Aquila. The L’Aquila text specifies only that the peak must be “as soon as possible” and omits the reference year against which goal the 50% global reductions by 2050 is to be calculated. In our rendering, its peak year is 2020, and the maximum annual rate of post-peak emissions decline is 6.0%. (The late peak requires very rapid reductions in order to reach its 50% in 2050 specification, and this despite its relatively larger budget.) The pathway's 2012 to 2100 CO2 budget is ~1600 GtCO2, which is well above the largest of the IPCC's budgets, the one that is given a 33% chance of staying below 2ºC. One can safely say that it is “very likely” to exceed 2ºC by 2100.
For much more information on all of this, including a comparison of these pathways to the IPCC's emissions budgets, see the Mitigation Pathway Overview.