The multi-component “green” McGill Paleoclimate Model (MPM), which includes interactive vegetation, is used to simulate the
next glacial inception under orbital and prescribed atmospheric CO
2 forcing. This intermediate complexity model is first run for short-term periods with an increasing atmospheric CO
2 concentration; the model's response is in general agreement with the results of GCMs for CO
2 doubling. The green MPM is then used to derive projections of the climate for the next 100 kyr. Under a constant CO
2 level, the model produces three types of evolution for the ice volume: an imminent glacial inception (low CO
2 levels), a glacial inception in 50 kyr (CO
2 levels of 280 or 290 ppm), or no glacial inception during the next 100 kyr (CO
2 levels of 300 ppm and higher). This high sensitivity to the CO
2 level is due to the exceptionally weak future variations of the summer insolation at high northern latitudes. The changes
in vegetation re-inforce the buildup of ice sheets after glacial inception. Finally, if an initial global warming episode
of finite duration is included, after which the atmospheric CO
2 level is assumed to stabilize at 280, 290 or 300 ppm, the impact of this warming is seen only in the first 5 kyr of the run;
after this time the response is insensitive to the early warming perturbation.