Using the MIT Integrated Global System Modeling ( IGSM) framework, which combines a human activity model with a climate model of intermediate complexity, the researchers project the climate impact of a “no climate policy” case and three scenarios that effectively extend the NDCs to 2100. The scenarios considered range from a pessimistic world where no further action is specified past 2030 to a world where the same level of commitment as in the Paris agreement is extended until the end of the century.

Assuming a climate system response to anthropogenic greenhouse gas emissions that’s of median strength, the three scenarios reduce the SAT in 2100 between 0.6 and 1.1 C relative to the “no climate policy” case. But because the climate system takes many years to respond to emissions reductions, in 2050 the SAT falls by only about 0.1 C in all three cases. Meanwhile, the rise in SAT since preindustrial times exceeds 2 C in 2053, and in 2100, reaches between 2.7 and 3.6 C — far exceeding the 2 C goal.