In this study we followed the emissions scenario described by the U.S. Climate Change Science Program (CCSP) scenarios exercise in their "Level 2" scenario. The stabilization levels of anthropogenic greenhouse gases in the atmosphere, as estimated by the MIT IGSM, were specified in terms of the allowable increase in radiative forcing in Watts per meter squared.
The emissions limits in this study were prescribed such that they were approximately consistent with a stabilization of atmospheric concentration of CO2 at the level of 550 parts per million (ppm). With the inclusion of the radiative forcing associated with other non-CO2 greenhouse gases, this stabilization level is approximately a 675 ppm CO2-equivalent limit.
In this hypothetical policy scenario, after the Kyoto period (2008-2012) it is assumed that all countries participate and that emissions reductions are achieved cost-effectively. We met the emissions constraint of the CCSP exercise exactly, but because the response of the Earth system is uncertain — carbon uptake on land and by the ocean, and other feedbacks on greenhouse concentrations, are uncertain — the concentrations of these gases in the atmosphere vary.
A useful way to summarize these emissions limits is in tons of emissions in CO2-equivalent allowed over the century. In this policy scenario the level of CO2-equivalent emissions is 4.2 trillion metric tons.
The MIT Joint Program has contributed to several Synthesis and Assessment efforts organized by the U.S. Climate Change Science Program (CCSP).
MIT Program participants were among the coauthors of the CCSP reports on Scenarios of Greenhouse Gas Emissions and Atmospheric Concentrations, and Global-Change Scenarios: Their Development and Use. And the MIT Integrated Global System Model was one of three models utilized in the CCSP analysis.
