How Many ‘Wedges’ Does It Take to Solve the Climate ‘Problem’?

by Marlo Lewis on January 11, 2013

in Blog, Features

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In An Inconvenient Truth (pp. 280-281), Al Gore enthused about a Science magazine study by Princeton economists Robert Socolow and Stephen Pacala. The study concluded that, “Humanity already possesses the fundamental scientific, technical, and industrial know how to solve the carbon and climate problems for the next half century.” Gore claimed the policies Socolow and Pacala recommend, “all of which are based on already-existing, affordable technologies,” could reduce emissions below 1970s levels.

But Gore could not know the solutions are “affordable,” because the authors did not attempt to estimate costs. The study basically shows that if political leaders can somehow coerce everybody to use less energy and adopt low- or zero-carbon energy technologies regardless of cost, they can significantly reduce emissions by 2054. We needed Princeton professors to tell us that?

If An Inconvenient Truth were a balanced presentation rather than a CGI-embellished lawyer’s brief, Gore would have mentioned that Socolow and Pacala’s (S&P) study was a response to an earlier analysis, also published in Science, by New York University Prof. Martin Hoffert and 17 colleagues.

Hoffert et al. found that all existing energy technologies “have severe deficiencies that limit their ability to stabilize global climate.” They specificially took issue with the UN IPCC’s claim that “known technological options” could stabilize atmospheric carbon dioxide (CO2) levels at 550 parts per million (ppm) or even 450 ppm over the next 100 years. Noting that world energy demand could triple by 2050, they found that zero-carbon technologies that can produce 100 to 300% of present world power consumption “do not exist operationally or as pilot plants.” Bottom line: “CO2 is a combustion byproduct vital to how civilization is powered; it cannot be regulated away.” They concluded that it is not possible to stabilize atmospheric CO2 concentrations and meet global energy needs “without drastic technological breakthroughs.”

I review this ancient history because Environmental Research Letters just published a study ‘updating’ (i.e. rebutting) the S&P analysis. The lead author is UC Irvine Prof. Steven Davis. One of three other co-authors is Martin Hoffert.

S&P estimated that seven ”stabilization wedges” could limit atmospheric CO2 concentrations to 500 ppm by 2054. The Davis team estimates it will take 19 and possibly 31 wedges to solve the climate ‘problem.’ In other words, the challenge is much more difficult than S&P believed.

But what, you may be wondering, is a “stabilization wedge”?

S&P depicted mankind’s emission trajectory on a graph. They estimated that if emissions could be held constant at 2004 levels, then atmospheric concentrations could be stabilized at 500 ppm in 2054. The area on the graph representing the growing gap between 2004 emissions and the projected increase in emissions over the next 50 years forms a triangle. S&P divide the triangle into seven wedges, each representing 1 gigaton of carbon (1 GtC) emissions in 2054 and 25 GtC in cumulative emissions over 50 years. Mankind could solve the climate ‘problem,’ S&P reasoned, by scaling up seven low- and zero-carbon technologies to the point where each avoids a cumulative 25 GtC by 2054.

Easier said than done! One of S&P’s strategies to achieve a stabilization wedge is to add double the current global nuclear capacity to replace coal-based electricity. However, although once predicted to be “too cheap to meter,” nuclear power is still not viable without subsidies and is not competitive with gas-fired electricity. The environmental movement, moreover, remains staunchly “no nukes,” and is unlikely to rethink its ideology in the post-Fukushima political climate.

Another strategy is to deploy carbon capture and storage (CCS) technology at coal power plants. Despite billions of dollars in government R&D support, no commercial-scale CCS coal power plant has been built. None today could operate without hefty subsidies. If hit with a carbon tax or a CO2 emissions standard, most utilities would find it cheaper to build new natural gas power plants than to build new coal plants with CCS.

A third S&P strategy is to increase wind capacity by 50 times relative to the mid-2000s, for a total of 2 million large windmills. The word boondoggle leaps to mind. If wind energy is such a great buy for consumers, why do 29 states have to mandate it? If it’s truly ’sustainable,’ why did the American Wind Energy Association (AWEA) assert that, despite enjoying government-guaranteed markets in more than half the states, the industry would crash unless Congress ponied up another $12.1 billion in special tax breaks?

Another strategy is to increase ethanol production 50 times. Subsequent research indicates that land conversions induced by ethanol production emit more CO2 than the petroleum displaced by ethanol consumption. Besides, even if ethanol were a low-carbon fuel, the scale up proposed – biomass plantations covering “an area equal to about one-sixth of the world’s cropland” – would intensify the already perilous fuel vs. food tradeoff and decimate millions of acres of forest and other wildlife habitat.

In the new study, “Rethinking Wedges,” Davis et al. note that since S&P was published in 2004, ”annual emissions have increased and their growth rate has accelerated, so that more than seven wedges would now be necessary to stabilize emissions.” More importantly, stabilizing emissions at current levels for 50 years would not be enough to limit CO2 concentrations to 500 ppm and, thus, avoid ‘dangerous anthropogenic interference,’ defined by climate negotiators as a warming of 2°C or more.*

So what would “solve the carbon and climate problem,” according to Davis et al.? You guessed it — “sharply reducing CO2 emissions over the next 50 years,” indeed, deploying enough wedges to achieve “near-zero emissions.” They estimate:

Given the current emissions trajectory, eliminating emissions over 50 years would require 19 wedges: 9 to stabilize emissions and an additional 10 to completely phase-out emissions. And if historical, background rates of decarbonization falter, 12 ‘hidden’ wedges will also be necessary, bringing the total to a staggering 31 wedges.

Figure explanation (from Davis et al. 2013): Idealization of future CO2 emissions under the business-as-usual SRES A2 marker scenario. Future emissions are divided into hidden (sometimes called ‘virtual’) wedges (brown) of emissions avoided by expected decreases in the carbon intensity of GDP by ~1% per year, stabilization wedges (green) of emissions avoided through mitigation efforts that hold emissions constant at 9.8 GtC y beginning in 2010, phase-out wedges (purple) of emissions avoided through complete transition of technologies and practices that emit CO2 to the atmosphere to ones that do not, and allowed emissions (blue). Wedges expand linearly from 0 to 1 GtC y from 2010 to 2060. The total avoided emissions per wedge is 25 GtC, such that altogether the hidden, stabilization and phase-out wedges represent 775 GtC of cumulative emissions.

What it means is that you can’t get there from here without fundamental technology breakthroughs — exactly what Hoffert et al. concluded in 2002. Over the next four decades the world will need multiple terawatts (trillions of watts) of new energy. None of the existing zero-carbon energies is up to the challenge:

CCS has not yet been commercially deployed at any centralized power plant; the existing nuclear industry, based on reactor designs more than a half-century old and facing renewed public concerns of safety, is in a period of retrenchment, not expansion; and existing solar, wind, biomass, and energy storage systems are not yet mature enough to provide affordable baseload power at terawatt scale. Each of these technologies must be further developed if they are to be deployed at scale and at costs competitive with fossil energy.

Filling up 31 wedges will require “deploying tens of terawatts of carbon-free energy in the next few decades.” That will entail “a fundamental and disruptive overhaul of the global energy system.” In short, “Current technologies and systems cannot provide the amounts of carbon-free energy needed soon enough or affordably enough to achieve this transformation.”

Davis et al. recommend an “aggressive set of policies” to “support energy technology innovation across all stages of research, development, demonstration, and commercialization.”

But if existing zero-carbon technologies cannot affordably be scaled up to meet current and projected global energy needs, how likely is it that technologies either not yet invented or as yet prohibitively expensive can affordably replace the world’s fossil-fuel infrastructure? And aren’t there significant risks to public health and welfare from policies “aggressive” enough to implement a “disruptive overhaul” of the energy infrastructure that supports the lives and livelihoods of billions of human beings? Rethinking Wedges is a mix of realism and wishful thinking, environmental precaution and regulatory recklessness.

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* Here Davis et al. follow the self-anointed ‘scientific consensus.’ For an alternative assessment of climate sensitivity (how much warming results from a given increase in CO2 concentrations), see Chip Knappenberger’s Lower Climate Sensitivity Estimates: Good News, Another Lower Climate Sensitivity Estimate (with Pat Michaels), and Climate Sensitivity Going Down. For an alternative assessment of climate change impacts, see Indur Goklany’s Trapped Between the Falling Sky and the Rising Seas: The Imagined Terrors of the Impacts of Climate Change.

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