it will take a massive mobilization to make progress. Hoffert explains: In a 2010 Science article, Hoffert also suggested that 18-25 wedges may be necessary to achieve the goal, given the higher rates of emission growth that have occurred since the original study, even if no new sources were added beginning in 2010. In June 2008, Joseph Romm argued in Nature magazine that "If we are to have confidence in our ability to stabilize carbon dioxide levels below 450 p.p.m. emissions must average less than 5 GtC per year over the century. This means accelerating the deployment of the... wedges so they begin to take effect in 2015 and are completely operational in much less time than originally modelled by Socolow and Pacala." A final criticism is that the Wedge Game focuses on technological fixes rather than fundamentally challenging the endless growth economy that is at the heart of global climate change. The 2007 IPCC reports state clearly that economic and demographic growth are the fundamental drivers of global climate change. Yet of the fifteen wedges developed by Pacala and Socolow, only one—halving the number of miles driven by the world's automobile fleet—might be considered a "demand reduction" wedge. None of their wedges treat population reduction. References Environmental education video games