Cumulative emissions of ~ 1000 GtC, sometimes associated with 2 °C global warming, would spur «slow» feedbacks and eventual warming of 3 - 4 °C with disastrous consequences.» (realclimate.org)
A global warming target is converted to a fossil fuel emissions target with the help of global climate - carbon - cycle models, which reveal that eventual warming depends on cumulative carbon emissions, not on the temporal history of emissions [12]. (journals.plos.org)
In contrast, the 1000 GtC scenario, although nominally designed to yield a fast - feedback climate response of ∼ 2 °C, would yield a larger eventual warming because of slow feedbacks, probably at least 3 °C. (journals.plos.org)