A carbon emission wedge is defined as emission of 25 Gigatons (25 billion metric tons) of carbon over 50 years, shaped as a wedge that starts at zero in 2010 and grows steadily to 1 Gigaton of Carbon emission per year (GtC/y) in 2060. The total emission of the linearly increasing 0 to 1 GtC emissions over 50 years is the average of 1/2 x 1 GtC/y x 50 years = 25 GtC total.
Robert Socolow and Stephen Pacala of Princeton defined a wedge in 2004 in Science, 13 August 2004, p. 968. They pointed out that 7 wedges of emission reduction would be needed to stabilize emissions starting then at 7 GtC per year for 50 years. Now, emissions have grown to 10 GtC per year, and 9 wedges of reduction of new power demand would be needed for stabilization at the present 10 GtC/y in 50 years.
In an investigation of what it would take to reduce emissions of carbon to essentially zero in 50 years, Steven J. Davis of UC Irvine, along with Long Cao, Ken Caldeira, and Martin I Hoffert have published an Open Access paper entitled Rethinking Wedges in Environmental Research Letters, 8 (2013) 011001. (Its approaching 2000 downloads, so people are rethinking.) They project that emissions would grow to 31 GtC/y by 2060, including increased emissions by China and Russia, which is a growth of 12 extra GtC/y by 2060 over even the Socolow and Pacala paper’s 9 GtC/y. Even to achieve stabilization at the present 10 GtC/y, 12 new wedges of reduction called Hidden wedges would be needed, by reducing the carbon intensity (amount of carbon needed to produce a dollar of GDP) by 1% a year.
Once the 12 + 9 = 21 wedges are achieved for stability at the present level, we want to accomplish the goal of reducing greenhouse gases to essentially zero and not exceed the total global warming of 2° C that the United Nations are focused on. Since we would have stabilized at the present 10 GtC/y, to reduce this to essentially zero would require a final 10 wedges of reduction. This is actually pretty simple arithmetic. I can’t legitimately reprint their figure here. Just imagine a paper fan with 31 front folds held sideways:
As long as you are imagining, imagine how we are going to find 31 wedges of emission free energy, each one of which is equal to 10% of what we are emitting now. Sensibly, the authors conclude “An integrated and aggressive set of policies and programs is urgently needed to support energy technology innovation across all stages of research, development, demonstration, and commercialization.” Being at a university, I would also call for training a vast segment of STEM students to be able to carry this out, as well as students in biology and earth system science to understand how the earth works in the relevant fields of response and adaptation.
