Late last year, in my "Dirty Coal, Clean Future" story, I discussed the famous "wedge" concept of what it would take to reduce global carbon emissions and thus stabilize the concentration of CO2 in the atmosphere. (That story was mainly about US-China efforts to use coal in less damaging ways -- efforts that are plowing ahead in China but now are largely being zeroed-out on the U.S. side for budgetary reasons.) The story said about the wedges:

>>Isn't "clean energy" the answer? Of course--because everything is the answer....

The best-known illustration of the need for an all-fronts approach is the "carbon wedge" analysis from the Carbon Mitigation Initiative at Princeton. Its premise is that to keep the carbon-dioxide level from going into the 500s, or twice its pre-industrial-age level, over the next 50 years, the world collectively will need to reduce its carbon-dioxide emissions by a total of about 26 billion tons per year. (Technically, CMI measures its goals in billions of tons of carbon contained within the carbon dioxide. For clarity, I've converted the figures.) To reach that total, CMI proposes seven "stabilization wedges" of a little less than 4 billion tons of carbon dioxide each. A 4-billion-ton "wedge" through efficiency efforts of all kinds; another wedge of that size through renewable power; another through avoiding deforestation and changing agricultural practices. Eventually it adds up. "There are many good options," Julio Friedmann, a geologist at Lawrence Livermore National Laboratory, told me soon after I first met him in Beijing two years ago. "But there are no unlimited options. Each is limited by cost, limited by scale, limited by physics and chemistry, limited by thermodynamics."<<

The scientist most associated with wedge analysis, Robert Socolow of Princeton, has just published a new paper saying that wedge-style thinking still applies. Unfortunately, he says, we now need two extra wedges-worth of carbon saving, for a total of nine, rather than the original seven, because that much more time has gone by without getting started. The revised illustration with caption, via Climate Central, shows how the wedge effect would have looked if it had started at the time of his original paper, in 2004 and how the trends look now.


The 2004 "wedges" paper assumed that the objective of global mitigation would require a flat emissions rate for 50 years, followed by a falling rate. Making the same heroic assumption today would result in substantial additional emissions.
To spell it out: the longer we wait, the harder it gets. John Mecklin, of the Bulletin of Atomic Scientists, says more about the implications -- as Socolow of course does in his new essay (also available here). That's all I have time for at the minute, but this is important.