Recent research has shown that once CO2 has been emitted to the atmosphere, it will take centuries for natural removal. Clearly, the longer we delay deep reductions in CO2, the greater the risk that total greenhouse gas emissions will exceed prudent limits for avoiding dangerous anthropogenic change. We evaluate the three possible technical approaches for climate change mitigation: emission reduction methods, post-emission draw down of CO2 from the atmosphere, and geoengineering. We find that the first two approaches are unlikely to deliver the timely reductions in CO2 needed, while geoengineering methods either deliver too little or are too risky. Given the deep uncertainties in both future climate prediction and energy availability, it seems safest to actively plan for a much lower energy future. We propose a general 'shrink and share' approach to reductions in both fossil-fuel use and carbon emissions, with basic human needs satisfaction replacing economic growth as the focus for economic activity. Only with deep cuts in energy and carbon can we avoid burdening future generations with the high energy costs of air capture. (C) 2009 Elsevier Ltd. All rights reserved.