Alternative Climate Wedges

This page explores alternative approaches to climate change mitigation focused on recognizing and embracing limits to growth. Your comments and suggestions are greatly appreciated!

In addition to the general discussion below, I develop six "alternative wedges" at greater length here: Air Travel Wedge, Carbon Tax Wedge, Economic Growth Wedge, Luxury Wedge, Population Reduction Wedge, Vegetarian Wedge

The Problem

There is a curious disconnect in climate change discourse, between explanations of the causes of global climate change (GCC) and discussions of possible solutions. On the one hand, it is widely acknowledge that the primary causes of climate change are economic and demographic growth. As the 4th Assessment Report from the Intergovernmental Panel on Climate Change (IPCC) succinctly puts it: “GDP/per capita and population growth were the main drivers of the increase in global emissions during the last three decades of the 20th century . . . At the global scale, declining carbon and energy intensities have been unable to offset income effects and population growth and, consequently, carbon emissions have risen” (Climate Change 2007: Mitigation (2007), Technical Summary, p.107). On the other hand, most proposals for climate change mitigation take population growth and economic growth as givens, beyond the realm of policymaking, and focus instead on technological efficiency improvements as the sole means of reducing green house gas emissions.

Climate scientists speak of the “Kaya Identity”: the four primary factors which determine overall greenhouse gas emissions. They are economic growth/per capita, population, energy used to generate each unit of GDP, and greenhouse gases generated per unit of energy. Over the past four decades, improvements in energy and carbon efficiency have been overwhelmed by increases in population and wealth. Here are the numbers, again according to the IPCC: “The global average growth rate of CO2 emissions between 1970 and 2004 of 1.9% per year is the result of the following annual growth rates:

population + 1.6%,

GDP/per capita + 1.8%,

energy-intensity (total primary energy supply (TPES) per unit of GDP) – 1.2%,

and carbon-intensity (CO2 emissions per unit of TPES) – 0.2%.” (ibid.)

Crucially, the IPCC’s projections for the next several decades see a continuation of these trends. More people living more affluently mean that under “business as usual,” despite expected technical efficiency improvements, greenhouse gas emissions will increase between 25% and 90% by 2030, relative to 2000 (ibid., p.111). If we allow this to occur, it will almost surely lock in global temperature increases of more than two degrees Centigrade over pre-industrial levels, exceeding the threshold beyond which scientists speak of potentially catastrophic climate change. Following this path would represent a moral catastrophe as well: the selfish over-appropriation and degradation of key environmental services by the current generation to the detriment of future ones, by rich people to the detriment of the poor, and by human beings to the great detriment of the rest of the living world.

A reasonable person reading the IPCC report and subsequent scientific literature on climate change would likely conclude that we are bumping up against physical and ecological limits. Given the dangers of catastrophic GCC, a prudent and moral response might be: “Wow! This is going to be hard. We need to start working on this problem with all the tools at our disposal. Increasing energy and carbon efficiency, to be sure. But also decreasing the pursuit of affluence and overall consumption; and stabilizing or reducing human populations. Maybe in the future we can grow like gangbusters again, maybe not. But for now, we need to make fewer demands on nature and see if even our current numbers are sustainable over the long haul. After all, our situation is unprecedented—7 billion people living or aspiring to live in modern, industrialized economies—and there is no guarantee that we aren’t already in ‘overshoot’ mode.”

Such convictions would only be strengthened by considering further evidence of global ecological degradation from the recent Millennium Ecosystem Assessment (MEA), including the depletion of important ocean fisheries, accelerating soil erosion, ongoing species extinctions throughout the world, the growth of immense “dead zones” at the mouths of many great rivers, and more. According to the MEA, humanity is currently degrading or utilizing unsustainably fifteen of twenty-four key ecosystem services.

However, neither GCC nor any of these other problems have led to a widespread re-evaluation of the goodness of growth. Regarding GCC, we have seen a near-total focus on technological solutions by politicians, scientists, the general public, and even environmentalists. I contend that this is a serious mistake. Because business as usual with respect to consumption and growth almost surely cannot avoid catastrophic GCC or meet our other global ecological challenges, we need to consider a broader range of alternatives that include slowing or ending growth. Failure to do so, will likely mean failure to avoid catastrophic global climate change.

The Wedge Approach

Of the many possible examples of mainstream approaches to climate change mitigation that we might consider, let us look at one of the most comprehensive, rigorous, and influential, Stephen Pacala and Robert Socolow’s “wedge” approach, first presented in “Stabilization Wedges: Solvingthe Climate Problem for the Next 50 Years with Current Technologies,Science 305 (2004): 968–972. Recent research and even a downloadable version of the “Carbon Mitigation Wedge Game” can be found at the website for the Carbon Mitigation Initiative.The wedge approach is a heuristic designed to help compare alternative mitigation schemes. Pacala and Socolow’s stated goal, in the face of numerous mitigation proposals and skepticism about whether any of them could succeed, was to provide a practical road map of choices that could facilitate successfully addressing the problem of GCC.

Each wedge in Pacala and Socolow's “stabilization triangle” repre­sents a technological change which, fully implemented, would keep one billion metric tons of carbon from being pumped into the air annually, fifty years from now. It would also prevent twenty-five billion metric tons of carbon from being released during the intervening fifty years. The authors figure eight such wedges would have to be implemented to keep atmospheric carbon from doubling and pushing past potentially catastrophic levels during this period. In order to fully address GCC, in the next fifty years, humanity would have to move to an economy where human carbon outputs did not exceed carbon uptakes in natural systems. The wedge approach buys us time and (allegedly) begins the transition toward such an economy.

Pacala and Socolow provide fifteen possible “wedges.” These include: doubling the fuel economy of the world auto fleet; replacing coal plants generating 1,400 gigawatts of power with natural gas plants; implementing carbon capture and storage at coal plants generating 800 gigawatts or at natural gas plants generating 1,600 gigawatts; deploying 2 million 1-megawatt-peak windmills (50 times current capacity); and substituting biomass fuel for fossil fuel by using 250 million hectares (1/6 of world cropland!) for ethanol production.

A strength of the wedge approach is that it allows us to specify the costs and benefits of different courses on climate action and thus choose intelligently between them. So far this has mostly meant asking which wedges are cheapest economically. But the approach could also allow us to compare alternatives based on environmental impacts, equitable sharing of costs and benefits, dangers of unintended side-effects, whether the alternatives increase or decrease humanity’s immoral hogging of resources that other species need to survive, or whatever criteria we deem relevant.

A weakness of the wedge approach, as it has been developed so far, is that the wedges proposed focus almost exclusively on technological fixes and efficiency gains. Not that there’s anything wrong with such efforts. But given that the primary causes of global climate change are unremitting economic and demographic growth, it makes sense to consider “alternative wedges” that target consumption reductions, population stabilization, and the moderation of economic growth itself.

Like most discussions of climate change, the wedge approach as developed to date simply takes for granted that our goal should be to accommodate more consumption by more people with less environmental impact. This goal is impossible to meet. Endless growth is impossible in a finite physical system, such as planet Earth. Our failure to consider limits to growth seems likely to lead to catastrophic GCC and to further delay in humanity’s necessary transition to ecological sustainability.


My paper “Beyond Business as Usual: Alternative Wedges to Avoid Catastrophic Climate Change and Create Sustainable Societieswas a first effort to formulate alternative wedges which recognize limits to growth. These wedges include eating-less-meat wedges, aviation wedges, carbon tax wedges, decreasing luxury consumption wedges, population stabilization wedges, and economic growth reduction wedges. Other papers which help develop these alternatives include "Reducing Consumption to Avert Catastrophic Global Climate Change: The Case of Aviation," "Climate Ethics and Population Policy: A Review of Recent Philosophical Work," Population growth and climate change: Addressing the overlooked threat multiplier and “The Potential Environmental Impacts of EU Immigration Policy: Future Population Numbers, Greenhouse Gas Emissions and Biodiversity Preservation.”

I present these wedges as a supplement to Pacala and Socolow’s techno-efficiency wedges, not as an (exclusive) alternative to them. In fact, I think the best mix of measures to prevent catastrophic climate change—best in terms of their justice, efficiency, and contribution to genuine sustainability—will include a mix of efficiency improvements and policies to reduce consumption, production and population.

These alternative wedges are works in progress, with some more well-worked-out than others. In the sub-pages below, I present some of my most recent calculations and thoughts regarding them. I would greatly appreciate any comments or criticisms. Feel free to write to me at

In the end, the case for deploying these alternative wedges rests on complex empirical and ethical judgments. But so, I think, does the case for not deploying them and instead focusing primarily on techno-fixes, the currently favored approach.