The size and scope of actions necessary to address climate change can cause paralysis and inaction. In the absence of public policy, emissions would grow to around 60 billion metric tons of carbon dioxide by the middle of this century from current emissions of roughly 30 billion metric tons per year. In order to achieve climate stabilization, most analysis recommends an emission reduction target of 50% to 100% by 2050 from today's levels. Politically, there has been progress. The United States House of Representatives recently passed the climate and energy bill, known as the American Clean Energy and Security Act. The incredible difference between the do-nothing, status quo trajectory and these targets can be daunting. This month on EarthTrends we will give an overview of the most commonly discussed technologies and practices that get us from here to there as well as a consideration of the associated costs of implementing these solutions.

The concept of a stabilization wedge was proposed by researchers at the Carbon Mitigation Initiative (CMI) to break up the overwhelming challenge of combating rising emissions into manageable pieces. CMI produced a graph with two cases of emission projections: a business-as-usual trajectory AND a climate stabilization trajectory. See Graph A on Figure 1 below. Each "wedge" represents a method of reducing carbon emissions by 1 billion metric tons per year by 2050. See Graph B on Figure 1.

Figure 1: Stabilization Wedges

The area between the business as usual line and the emission target line represented by the green triangle is the necessary amount of carbon reduction. It is known as the stabilization triangle. This triangle can then be divided up into theoretical slices know as stabilization wedges. A stabilization wedge is a technology or practice representing 1 GtC/year of emission reduction by mid-century which could be scaled commercially today. Cumulatively, one wedge over the roughly 50 year period represents 25 GtC of reduced carbon emissions.

Source: S. Pacala and R. Socolow, 2004

Wedges help us understand and assess the options for mitigating carbon dioxide emissions. Some technologies and practices have the potential to be multiple wedges, although no one wedge has the potential to solve the whole problem. This notion prevents a common desire to believe in a single silver bullet to solve the problem. Rather, it encourages the solution to be viewed as "silver buckshot."

The goal and assumptions of a stabilization analysis determine the number of wedges necessary. The emissions target, the baseline business-as-usual scenario and the year action is initiated affect the number of wedges to achieve the desired climate goal. Forecasts show a range of 7 to 14 wedges necessary for stabilization depending on these goals and assumptions. It should also be noted that the implementation of one wedge may impact the emission reduction potential of another. For example, as emissions are reduced from decarbonizing electricity generation, the emissions benefit from energy efficiency is reduced.

Since the time of the original stabilization wedge analysis in 2004, some wedges have fallen out of favor. Excitement about hydrogen as a transportation fuel has been tempered by advances in battery cycles for plug-in hybrids. And there continues to be concerns regarding the true emission profiles of biofuel crops.

A recent assessment by the IEA, Energy Technology Perspectives 2008, offers 17 technologies across 8 categories shown in Figure 2 below. The IEA does not present this as a stabilization wedge analysis with a corresponding 1 billion tC/year reduction by 2050. However, the analysis does show a clear pathway using technologies and practices that create "wedges" of climate mitigation over time.

Figure 2: IEA Projected Emissions

Note: Emissions are in Gt of CO2, not Gt of C.

Source: International Energy Agency, 2008

The Stabilization Wedges

Demand-Side Efficiency
Energy efficiency is often the first option discussed for emission reductions because the economic benefits can be cost-effectively realized. Each of the following alternatives reduces emissions by 1 GtC/year by mid-century:

• Increase fuel efficiency from 30 mpg to 60 mpg for the 2 billion cars that will be on the planet;
• Decrease car travel for the 2 billion 30-mpg cars from 10,000 to 5,000 miles per year through investments in mass transit, urban planning and telecommuting; or
• Implement efficiency measures that cut energy use by one-fourth in buildings and appliances.

A different assessment asserts that a wedge can be produced from combined heat and power. Also known as cogeneration, this method increases the efficiency of power production by using the waste heat to heat buildings and water supplies.

EarthTrends contains the following data products related to efficiency:
Energy Overview 2005
Energy Consumption by Sector 2005
Energy Consumption: Total energy consumption per capita
Electricity: Electricity consumption per capita
Energy Consumption: Residential energy consumption per capita
Transportation: Road sector energy consumption
Transportation: Road sector energy consumption per distance traveled
Transportation: Motor gasoline consumption per capita
Transportation: Diesel oil consumption per capita

Renewables
Decarbonising the electricity supply through implementation of renewable energy technology is another approach to achieve emission reductions. Stabilization wedges exist in the following technologies:

• Add 2000 GW of peak wind capacity to displace electricity from coal;
• Add 2000 GW of peak solar photovoltaic capacity to displace electricity from coal;
• Displace current transport fuels with hydrogen fuel from the electrolysis of water using wind power of 4000 GW; or
• Add 250 million hectares of land for biofuels. This is roughly 100 times the current production of ethanol in Brazil or the U.S. and would consume about one-sixth of the world’s current cropland.

Another analysis states 3 wedges could be obtained from concentrated solar power. It also shows that another 2000 GW wedge of wind for direct electrification of plug-in hybrids can displace 4000 GW of wind for the production of hydrogen fuel.

The use of biofuels as an emission mitigation strategy remains contested due to land-use change issues. For example, the US Environmental Protection Agency is in the process of determining which biofuels will qualify under the Renewable Fuels Standard mandate. Under this mandate, the biofuel must reduce emissions by 20 percent to qualify as a renewable fuel although some quantities are exempt from this test.

EarthTrends contains the following data products related to renewable energy:
Energy Consumption by Source: Solar, wind, and wave
Agriculture and Food
CO2 Emissions by Source: Cumulative emissions from land use change

Other Energy Solutions
The CMI also offers other wedges related to electricity production:

• Fuel switching, i.e., changing from coal to natural gas by replacing 1400 GW of coal power plants (at 50% efficiency) with natural gas power plants;
• Add 700 GW of nuclear power, which is about twice the current capacity; or
• Produce electricity from coal at 60% efficiency assuming twice as much electricity from coal will be necessary in the future.

EarthTrends contains the following indicators related to electricity production:
Energy Consumption by Source 2005
Carbon Dioxide Emissions by Source 2005
Energy Consumption by Source: Coal and coal products
Energy Consumption by Source: Natural gas
Energy Consumption by Source: Nuclear

Forest and Soil Management
Deforestation reduces the Earth's ability to sequester carbon because crops, grasslands and drylands generally store less carbon than forested areas. This reduction in carbon sequestered as biomass means an increase in atmospheric CO2 concentrations. Additionally, trees have many positive effects regarding climate change adaptation such as reduced desertification and improved watershed conservation. There has been significant research and discussion on land-use emissions as mentioned above. The following practices create a half wedge according the 2004 analysis at CMI:

• Decrease tropical deforestation to zero;
• Reforesting or afforesting approximately 250 million hectares in the tropics or 400 million hectares in the temperate zone; or
• Establish 300 million hectares of new tree plantations.

Also, a whole stabilization wedge can be obtained by applying conservation tillage to all cropland globally.

EarthTrends contains information on land use in the Forests, Grasslands and Drylands topic area.

Carbon Capture Storage (CCS)
CCS is any technology that can be used to capture CO2 from the point source and then transport it to appropriate locations and inject it into deep subsurface geological formations for isolation from the atmosphere. The CMI also foresees many wedges available with the use of CCS:

• Use CCS for 800 GW from coal power plants or 1600 GW from natural gas power plants;
• Use CCS while producing 250 million metric tons of hydrogen per year from coal or 500 million metric tons of hydrogen per year from natural gas; or
• Use CCS at synfuel plants producing 30 million barrels of synfuel a day from coal.

Other
Some suggest another wedge through albedo management of surfaces. Most of the sun's energy arrives as short-wave energy that can penetrate the Earth's atmosphere. It is then absorbed by the Earth's surface and radiated as long-wave energy which mostly gets absorbed in the atmosphere by the greenhouse effect. By reflecting a portion of this energy as short-wave energy before it is absorbed by Earth's surface, we can reduce some of the energy that becomes heat. This short-wave reflectance can be achieved by making pavement, rooftops, and even cars white or other "cool" colors.

Cost
There is no explicit discussion of cost in the stabilization wedge analysis. McKinsey & Company have created a GHG abatement cost curve to determine costs of specific abatement technologies and strategies. Notice that efficiency measures actually create negative costs (aka savings), while CCS technologies are some of the more expensive methods for reducing carbon dioxide emissions.

Figure 3: GHG Abatement Cost Curve

For larger image click here

The curve in Figure 3 depicts a stabilization analysis by using a myriad of approaches that are likely to available by 2030. This curve shows on the y-axis the cost per metric ton of carbon dioxide equivalent abated for each technology and practice. Those technologies and practices that are below the x-axis represent benefits and are usually efficiency measures. The higher cost technologies are represented by the right side of the graph and contain many of the CCS applications. If you subtract the area of the curve below with x-axis with the area above the x-axis you obtain the total cost in 2030 to achieve the stabilization target.

Source: McKinsey and Company, 2009

Why aren’t these economically beneficial technologies and practices being exploited in the real world? Some economists would argue that implementation costs, such as transaction and program costs, are not being included in the price. Additionally, across the billions of investment decisions that have to be made, market imperfections exist. These include information deficiencies about savings opportunities as well as weak incentives for the production of energy efficient goods and services since producers do not obtain the long-term economic benefits of their use. Availability of capital for these investments and shorter payback periods, especially in current market conditions, are also barriers to adoption. (McKinsey and Company, 2009)

McKinsey and Company estimates that the cost to implement all possible abatement technologies and practices would be between €200 and €350 billion (US$285 to $500 billion) a year by 2030 which would be 0.4 % of the forecasted Gross World Product (GWP) in 2030. (McKinsey and Company, 2009) Another estimate by IEA forecasting to 2050 (depicted for the scenario in Figure 2), approximates a cost of 1.1% of GWP each year from now until 2050. This averages to about $1.1 trillion per year. It is important to note that their analysis states that "this expenditure reflects a re-direction of economic activity and employment, and not necessarily a reduction of GDP." (OECD/IEA, 2008)

There are many alternatives amongst the possible wedges to be chosen and there is no lack of technological and management fixes to the problem of climate change. As the Executive Director of IEA states, "the primary scarcity facing the planet is not of natural resources nor money, but time. We will need to start putting our words and commitments into actions. Delay is no longer an option. It is time to act."

Related Links
Stabilization Wedges: Solving the Climate Problem for the Next 50 Years with Current Technologies
International Energy Agency Technology Perspectives 2008, Scenarios and Strategies to 2050
Pathways to a Low-Carbon Economy: Version 2 of the Global Greenhouse Gas Abatement Cost Curve
Carbon Mitigation Initiative