Rethinking Wedges: We Need A Lot of Clean Energy To Stabilize Near 2°C Warming So We Better Start Deployment ASAP

A new study underscores the point that we need to start deploying every last bit of carbon-free energy starting ASAP to have a reasonable chance of avoiding catastrophic levels of carbon pollution. But the paper, “Rethinking wedges,” suffers from two flaws.

First while it asserts “Current climate targets of 500 ppm and 2°C of warming” require “deploying tens of terawatts of carbon-free energy in the next few decades,” it seems to use this to argue for more research and development, rather than massive deployment. In fact, while everyone agrees we need to spend more on R&D, it’s our much vaster underspending on deployment that is launching us headlong toward catastrophe. And, of course, deployment is the best driver of innovation (as I discuss here).

Second, the paper appears to confuse what a wedge is and then compounds that confusion by introducing the concept of “hidden wedges,” which I don’t believe is a meaningful concept (if you understand what a wedge really is). The fact is that we probably need 1o to 20 terawatts of carbon-free energy over the next 50 years to have a shot at 450 ppm or lower — but a fair chunk of that can be efficiency and conservation (as I discuss here).

In any case, the need for massive deployment of carbon-free energy starting now is one that has been made by countless independent analyses. Even the traditionally staid and conservative the International Energy Agency explained three years ago that “The world will have to spend an extra $500 billion to cut carbon emissions for each year it delays implementing a major assault on global warming.”


A 2011 report found that “California can achieve emissions roughly 60% below 1990 levels with technology we largely know about today if such technology is rapidly deployed at rates that are aggressive but feasible.” A recent report by PricewaterhouseCoopers finds we’re headed to 11°F warming and even 7°F requires “Nearly Quadrupling The Current Rate Of Decarbonisation.”

The abstract of this new study by Davis, Cao, Caldeira, and Hoffert, to be published Wednesday in Environmental Research Letters asserts:

Stabilizing CO2 emissions at current levels for fifty years is not consistent with either an atmospheric CO2 concentration below 500 ppm or global temperature increases below 2C. To achieve these targets, solving the climate problem requires that emissions peak and decline in the next few decades, and ultimately to near zero. Phasing out emissions over 50 years could be achieved by deploying on the order of 19 ‘wedges’, each of which ramps up linearly over a period of 50 years to ultimately avoid 1 GtC/yr of CO2 emissions. But this level of mitigation will require affordable carbon-free energy systems to be deployed at the scale of tens of terawatts. Any hope for such fundamental and disruptive transformation of the global energy system depends upon coordinated efforts to innovate, plan, and deploy new transportation and energy systems that can provide affordable energy at this scale without emitting CO2 to the atmosphere

This notion of needing 19 wedges to go to zero emissions in 50 years is very compatible with my analysis a few years ago that we need 12–14 wedges squeezed into four decades to take emissions down some 50% by 2050.

But of course I conclude, as do the original inventers of the wedge concept, that any hope for deploying so many wedges so rapidly depends crucially upon … rapid deployment, rather than R&D! See also “The breakthrough technology illusion.”


This ERL paper is a response to the original 2004 wedges paper by Princeton Professors Socolow and Pacala. The ERL authors (mistakenly) believe that “An unfortunate consequence of their paper, however, was to make the solution seem easy.” In fact, no serious analyst I know came to that view. Quite the opposite.

A 2007 Keystone report concluded that just one wedge of nuclear power “would require adding on average 14 plants each year for the next 50 years, all the while building an average of 7.4 plants to replace those that will be retired” — plus 10 Yucca Mountains to store the waste. Socolow himself often pointed out that one wedge of carbon capture and storage would require a flow of CO2 into the ground equal to the current flow of oil out of the ground.

So no, it was never going to be “easy.” Socolow has made that point to anyone who would listen to him — and I’ve interviewed him a number of times: See my May 2011 post, Socolow reaffirms 2004 ‘wedges’ paper, urges aggressive low-carbon deployment ASAP and my September post, Socolow Re-Reaffirms 2004 ‘Wedges’ Paper, Urges ‘Monumental’ Levels of Clean Energy Deployment ASAP.

What he and Pacala were trying to demonstrate was not that it would be easy but rather that it could be done using existing or near-term technology and that we had to start deploying immediately. The title of the paper was “Stabilization Wedges: Solving the Climate Problem for the Next 50 Years with Current Technologies.”

It is baffling that this new paper simultaneously asserts we need far more wedges than Socolow does — in part because we have delayed deployment for so long — and then concludes that means R&D is the big missing piece in our climate strategy. Indeed, the article asserts “After eight years of mostly delay, the action now required is significantly greater.” But then it focuses its recommendations on innovation and R&D, not on how we start the mass deployment ASAP.

Again, everyone thinks we need more R&D, but it is the deployment gap that is 10 times larger and far much more problemmatic. Indeed, if we increased R&D by a factor of 10 but left deployment the same, we would certainly fry our agricultural system and destroy modern civilization. If we increased carbon-free deployment by a factor of 10 but left R&D the same, we would at least have a serious shot at not destroying a livable climate. Obviously we should do both, but the deployment is far more important and for more urgent


It also appears to me the ERL paper confuses what a wedge is — a very common problem. That leads the authors to overstate how much carbon-free power is needed — a problem exacerbated by their failure to discuss or even mention energy efficiency or conservation, both of which will likely be major contributors to addressing the climate problem over the next 50 years. It also leads the authors to introduce the concept of “hidden wedges, which I believe is not a meaningful term (as they define it). Explaining how and why the authors were confused cannot be done simply or quickly. I’ll explain it as best I can in a later post — although readers who are keenly interested can get the gist of it by reading this 2008 post, “Is 450 ppm politically possible? Part 2.5: The fuzzy math of the stabilization wedges.” The key point is that Socolow and Pacala basically defined their original wedges in the power sector as requiring about three quarters more power than they in fact needed — if the goal is to deliver 1 GtC/yr of CO2 savings 50 years from now by replacing existing coal plants. More later.