The Earth's Climate — Rethinking "Rethinking Wedges"

Rethinking Wedges is a paper which appeared recently in the journal Environmental Research Letters (Vol. 8, No. 1, January-March, 2013). I was going to title this post Is Humanity Fucked?, but chose to refrain from such vulgar sensationalism. While the title I chose is faithful to the subject matter, the title I did not use is more faithful to its spirit.

I will have to go through a complex argument, so I hope you have the time and patience to follow the text. Let's get right to it. We shall require two technical terms, one from the paper and one of my own devising. First, what is a climate stabilization wedge?

In 2004, Pacala and Socolow published a study in Science arguing that 'humanity can solve the carbon and climate problem in the first half of this century simply by scaling up what we already know how to do'. Specifically, they presented 15 options for stabilization wedges that would grow linearly from zero to 1 Gt [gigaton, = 10¹² kilograms] of carbon emissions avoided per year over 50 years.

The solution to the carbon and climate problem, they asserted, was to deploy the technologies and/or lifestyle changes necessary to fill all seven wedges of the stabilization triangle. They claimed this would offset the growth of emissions and put us on a trajectory to stabilize atmospheric CO₂ concentration at 500 ppm if emissions decreased sharply in the second half of the 21st century.

Implementing any stabilization wedge presents a considerable, daunting challenge for humanity. You can read the original paper (pdf) to see what I mean.

The target for avoiding dangerous climate change in Pacala and Socolow (2004) was 500 ppm (parts-per-million) of CO₂ in the atmosphere, with a concomitant warming of 2 °C. This allows us to define the term fucked.

Humanity is fucked if there is no hope of avoiding a climate regime which makes the Earth uninhabitable for large, big-brained, bipedal, primates like Homo sapiens. Such an outcome will eventually come to pass if CO₂ in the atmosphere exceeds 500 ppm (parts-per-million) with a concomitant increase in the Earth's surface temperature of 2 °C or more with respect to the pre-industrial conditions. (Other sufficient conditions, for example, the wholesale destruction of marine ecosystems, would fulfill this definition as well, but I am not concerned with those subjects today.)

Let us now go through the logic of Rethinking Wedges. I have left out a lot of unnecessary detail which is available in the paper itself.

1.  The authors assume the IPCC's (SRES) A2 marker scenario, which is a high-growth/high-emissions scenario going forward in the 21st century (but not nearly the highest). Why did they choose A2?

In the first half of this century, the A2 scenario is near the center of the plume of variation of the SRES emissions scenarios. Indeed, actual annual emissions have exceeded A2 projections for more than a decade. During this period, strong growth of global emissions has been driven by the rapid, carbon-intensive growth of emerging economies, which has continued despite the global financial crisis of 2008–9. For these reasons we believe that, among the SRES scenarios, A2 represents a reasonable 'business-as-usual' scenario. [See the figure below].

2.  The authors ran the HadCM3L climate model (from the Hadley Center of the UK Met Office) in combination with the A2 scenario, which demonstrated that Pacala and Sololow's original seven wedges are no longer adequate to avoid the fucked target.

Outcomes under A2 and with 9 stabilization wedges. Not even 9 wedges will do the trick with respect to CO₂ in the atmosphere (ppm, left frame), but the temperature increase comes in below 2 °C (right frame, blue line). But also note the orange and blue vertical bars showing the standard 2-sigma margin of error. It is possible we would see a 2 °C warming even if we implement 9 stabilization wedges.

3.  The authors conclude that CO₂ emission must peak and decline within the next 20 years. Emissions must be reduced to zero by 2060 (second graph below).

4. To accomplish the required peak and decline, and the subsequent phase-out, the authors conclude that we must implement 19 wedges, not 7 as Pacala and Sololow originally thought in 2004.

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.

The original 7 wedges can not stabilize the amount of CO₂ in the atmosphere at or  below the desired target (500 ppm) because total emissions have increased at a rapid rate over the last decade, mainly due to rapid industrialization in the "emerging" economies, particularly China.

5.  The authors conclude that current technologies and systems can not provide the amounts of carbon-free energy required to support the A2 growth scenario.

Filling this many wedges while sustaining global economic growth would mean deploying tens of terawatts of carbon-free energy in the next few decades.

Doing so would entail a fundamental and disruptive overhaul of the global energy system, as the global energy infrastructure is replaced with new infrastructure that provides equivalent amounts of energy but does not emit CO₂.

Current technologies and systems cannot provide the amounts of carbon-free energy needed soon enough or affordably enough to achieve this transformation.

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. No matter the number required, wedges can still simplify and quantify the challenge.

And that concludes our summary of Rethinking Climate Wedges.

Commentary

The first thing we are struck by is that the authors urge the adoption of an "integrated and aggressive set of policies" starting now while making two crucial assumptions: 1) current energy technology will not cut the mustard; and 2) the world will likely follow the A2 economic growth/CO₂ emissions scenario. But if these assumptions are valid, there is no hope whatsoever that tens of terrawatts of carbon-free energy can be deployed in the next 2 decades. Not a snowball's chance in Hell. That is the painful lesson of recent experience since Pacala and Socolow's 2004 paper. Therefore, under these assumptions, we are entitled to conclude that humanity is fucked, in the sense defined above.

Despite this unhappy and unavoidable conclusion, the proposed solution urges humanity to do more of the same thing which has obviously not worked up to now (deployment of alternative energy sources, more technological innovation in energy systems). Thus the thinking of these scientists is constricted in a way that demands explanation. There is only one plausible path to salvation, which the authors never consider—the A2 economic growth scenario must be sacrificed if humanity is to avoid being fucked. And at this late date, halting and reversing humanity's energy demands may not solve the climate problem either.

Otherwise, humanity is Waiting For The Miracle.

To be fair, the authors may indeed have thought about the problems accompanying endless growth. There are two broad possibilities.

1.  These scientists are indeed aware that pursuing the A2 growth scenario (or something like it) is the fundamental problem. In this case, there are 3 possibilities—

• The authors don't think it is appropriate for them to suggest that economic growth must be restrained.
• The authors don't think anyone would take them seriously if they made such a suggestion.
• The authors think it simply doesn't matter what they think about economic growth because the issue is out of their hands.

2. These scientists are blissfully unaware that striving for endless economic growth on a finite planet is the fundamental problem, and impossible to boot.

There is no way to know what's going on in the authors' heads, but I strongly suspect that possibility #2 (cluelessness) reflects their thinking on the subjects of growth, climate and energy. Perhaps we should ask them.

In order, the authors of Rethinking Wedges are—

Steven Davis, lead author, Department of Earth System Science, University of California, Irvine, Irvine, CA 92697, USA.  E-mail: [email protected]

Long Cao, Department of Earth Sciences, Zhejiang University, Hangzhou, Zhejiang Province, 310027, People's Republic of China. E-mail: [email protected]

Ken Caldeira, Department of Global Ecology, Carnegie Institution of Washington, Stanford, CA 94305, USA. E-mail: [email protected]

Martin I. Hoffert, Department of Physics, New York University, New York, NY 10003, USA. E-mail: [email protected]

Bear in mind that the issue on table is whether humanity is fucked or not.

You can ask them if you like, and direct them to this post. I have better things to do.

 

Comments

[John D]

It's amazing how many people think we can have limitless growth as soon as we get to 'clean energy'. I am convinced that if we found a way to produce free clean energy tomorrow we would still find a way to extinct ourselves. We would cut down every forest we could find and build McMansions and shopping malls. The world's population would grow until we were sitting on top of each other. And of course we could go to war with limitless firepower.

In the end, it all comes down to the false paradigm of infinite growth. Even smart scientists don't want to go against this religion.