Tuesday, September 13, 2011
As part of introducing my climate change class to mitigation, we play Stephen Pacala and Robert Socolow's Stabilization Wedge Game. It works well, but it requires some updating.
A little background: In 2004, Pacala and Socolow (P&S) published an important article in Science that conceptualized the world’s need to reduce greenhouse gas emissions as the task of choosing wedges, where each wedge is a strategy or technology that would avoid the emission of 25 gigatons of carbon (or about 92 gigatons of CO2) over a 50 year period. P&S posited that seven wedges would be necessary to stabilize the atmospheric concentration of carbon dioxide below 500 ppm. They set forth 15 wedge possibilities: for example, doubling the fuel efficiency of the world’s cars; increasing by 50 times our current solar power generation capacity; and eliminating tropical deforestation. To make the ideas in the article accessible to all, they developed the Stabilization Wedge Game, in which groups discuss wedge options and choose which seven they want. (And don’t miss the hilarious music video below!)
I started using the game in my climate change law class in 2008, and it has worked well with some necessary updating. In 2009, the authors themselves updated the game. Because emissions had grown since 2004, the game was updated to require that players choose eight wedges rather than seven. In my class, we still play the game with eight, but it is important to know that other scientists have found that many more wedges will actually be needed. Joe Romm has blogged that we need 12 to 14 wedges in four decades to keep CO2 concentrations under 450 ppm. In 2010, another article in Science argued that P&S were too conservative in their baseline assumptions and that 18 to 25 wedges are actually needed.
Also, it is not just the number of wedges, but also the substance of wedges that requires updating. Here are the changes that I made this year, drawn primarily from blog posts here, here and here by Joe Romm at Climate Progress.
1) I eliminated several of the original wedges, namely Carbon Capture and Storage (CCS) Hydrogen, CCS Synfuels, and Wind Hydrogen. CCS and hydrogen technologies have not turned out to be as feasible as the authors thought. I retain the wedge that involves CCS from traditional fossil fuel plants.
2) I added the following 4 wedges:
Forest storage: A wedge is gained by replanting forests over an area the size of the continental US;
Wind for vehicles: A wedge is gained by installing 2000 GW of wind capacity to power plug-in hybrids and electric vehicles. This amount is about 40-times the wind capacity we have today;
White roofs: Turning all of the world’s roofs and pavements “light” over the next 20 years provides an albedo change that offsets about a wedge-worth of emissions;
Concentrated solar power (solar thermal electric): A wedge requires 2000 GW. Currently about 1.2 GW are online worldwide, see list of plants worldwide.
If you want to use this game in your classes, you might also be interested in a previous post of mine on the Teaching Climate Law blog with some further ideas for discussion after the game is played.
- Lesley McAllister