Scenarios of Global Change: Integrated Assessment of Climate Impacts

Using the MIT Integrated Global System Modeling (IGSM) framework, we assess the climate impacts of emission scenarios exhibiting global mean surface temperatures ranging between 2.4°C and 4.3°C above pre-industrial by 2100. We compare the outcomes from these forward-looking scenarios against the common goal described by the target-driven scenario of 2°C. Without further policy measures, the agreement at COP-21 in Paris is projected to result in a 3.5°C increase in global temperature in 2100 relative to pre-industrial levels. Scenarios developed by Shell International (called Mountains and Oceans) exhibit a substantial movement towards temperature stabilization, as they result in increases of only 2.4–2.7°C by 2100. Valuable components of these scenarios include a substantial shift to renewable energy and deployment of carbon capture and storage (CCS). These scenarios are successful in mitigating a large portion of water stress impacts and air pollution damages. They also significantly mitigate increases in ocean acidity. These projections show the significant value of policies that do not quite reach 2°C stabilization, but fall substantially close to that target by the end of the century. The challenge of meeting the Paris Agreement’s aspiration to limit warming to 1.5°C is monumental, yet may be desirable if societies see the 2°C impacts, described here, as running too much risk.