With the passage of CoP21, the world is leaving a relatively inactive stage and entering a second stage characterized by broad-based efforts to reduce greenhouse gas emissions. A third stage of reductions will almost certainly be required. This should chart a feasible path to a stabilized climate and put in place the necessary policy architecture for following that path, marking a global tipping point where effective climate change mitigation is no longer a goal but an accepted fact, with broad implications for behaviour and decision-making, not least a massive reduction in the resources allocated to prospecting for new fossil fuel reserves. A clear proximate operational challenge for achieving this tipping point involves effective implementation of country Intended Nationally Determined Contributions (INDCs) with attendant information needs. Looking further ahead, four key research frontiers are presented, focused on achieving this tipping point and entering the third stage of emissions reductions.