C-Learn, developed by the coalition group Climate Interactive, is a three-region climate simulator that allows users to input targets for fossil fuels emissions, emissions from deforestation, and reductions from afforestation. The app then outputs the expected results for atmospheric CO2 concentrations and global temperature. The simulator is a free, public version of the more complicated C-ROADS, a tool designed to help policymakers compare the predicted effects of particular climate change mitigation policies.

Although interesting, C-Learn notably lacks the option to input assumptions regarding population growth rates, let alone those concerning more nuanced factors such as age structure, urbanization rates, or household size, the importance of which were recently discussed at the Wilson Center by the National Center for Atmospheric Research‘s Brian O’Neill. Population is a significant factor in determining what can be expected as reasonable emission targets and the failure to include space for demographic assumptions is a significant short-coming.