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Stephen Pacala

15 October 2005
Stephen Pacala

In the August 2004 issue of Science, Stephen Pacala and Robert Socolow of Princeton's Carbon Mitigation Initiative published a paper identifying 15 existing technologies that could each prevent 1 billion tons a year worth of carbon emissions by 2054. Pacala and Socolow have created a graph that divides the problem into the seven 1 billion-ton-per-year "wedges" which are required to halt the rise in greenhouse gas emissions, and stabilize the concentration of carbon dioxide in the atmosphere at 500 parts per million (ppm) (see figures below).

Their findings provide a strong counter to the argument that major new technologies need to be developed before significant mitigation of emissions can begin.

The existing mitigation technologies highlighted in their article include:

  • Doubling fuel efficiency of 2 billion cars from 30 to 60 mpg
  • Decreasing the number of car miles traveled by half
  • Using best efficiency practices in all residential and commercial buildings
  • Producing current coal-based electricity with twice today's efficiency
  • Replacing 1400 coal electric plants with natural gas-powered facilities
  • Capturing and storing emissions from 800 coal electric plants
  • Producing hydrogen from coal at six times today's rate and storing the captured CO2
  • Capturing carbon from 180 coal-to-synfuels plants and storing the CO2
  • Adding double the current global nuclear capacity to replace coal-based electricity
  • Increasing wind electricity capacity by 50 times relative to today, for a total of 2 million large windmills
  • Installing 700 times the current capacity of solar electricity
  • Using 40,000 square kilometers of solar panels (or 4 million windmills) to produce hydrogen for fuel cell cars
  • Increasing ethanol production 50 times by creating biomass plantations with area equal to 1/6th of world cropland
  • Eliminating tropical deforestation and creating new plantations on non-forested land to quintuple current plantation area
  • Adopting conservation tillage in all agricultural soils worldwide

Although their current study did not examine the costs of scaling up each of the 15 possible technologies, Pacala and Socolow point out that implementing the measures would likely generate economic benefits, including creating new industries, reducing the U.S. dependence on foreign oil and lessening the need for other pollution-control expenses associated with burning coal and other fossil fuels.

Pacala and Socolow's research is part of the Carbon Mitigation Initiative (CMI), a project in the Princeton Environmental Institute funded by $20 million in grants from BP and Ford Motor Co.

The Climate Group interviewed Stephen Pacala to learn more about the CMI's work on practical solutions for mitigating greenhouse gas emissions.

Which of the 15 wedges would you prioritize initially?

There are two ways to answer that question. If you talk to almost any economist they will say that you have to put a price on carbon so that the market can decide which wedges to prioritize, based on which are the cheapest options. However, if one were designing a long-term sustainable solution, there would be some wedges that you would stress over others.

Some of the wedges we identified in the paper are temporary measures, such as conservation tillage in agricultural soils and forest planting. This is because eventually the soils will run out, or you will run out of places to plant forest. These options will only provide one wedge, and will have to be replaced with something after they are used up. On the other hand, if you reduce demand through increased energy efficiency, this is a permanent measure. This is because there is a market incentive that once the efficiency improvements exist they will stay in place forever. For long term policy, some of the wedges are better than others because of their permanence.

Personally, more than anything I want the climate problem solved. For this reason, I believe that we need to use everything at our disposal. We need to do it because it is the cheapest way to do things but also because when the field becomes open, there are many more stakeholders who develop and recognize a vested interest in tackling this problem.

So far we have vested interests weighing very heavily in this debate who think they are going to lose by reducing their greenhouse gas emissions. What we need now are vested interests on the other side to add their voices. For me the smorgasbord of wedges has a number of advantages: it has the virtue of pragmatism, it has the virtue of lowest cost, and it has the virtue that it brings together the largest possible coalition.

Are there wedges that didn't make it into the paper?

For efficiency improvements we had only three examples and there were many more we could have added in. It is amazing how much of a wedge you get just out of replacing the remaining incandescent light bulbs with compact fluorescents. Also the number of options for biological sequestration is really large so they were not all included.

The primary criterion for inclusion was that the technologies had to already be deployed at the industrial scale. However, hydrogen production from coal was one exception. There is no big industrial example that makes hydrogen and sequesters the CO2, but the pieces for this technology are already in place. An enormous amount of hydrogen is currently being produced in industrial facilities using the chemistry of carbon capture, which stores the captured CO2 under pressure in tanks. All you would have to do would be to turn the pipe over and inject the CO2 into the ground, a practice which has been in place for over 40 years as part of enhanced oil recovery.

What wedges are the least worth pursuing, and would it be the ones with the shortest lifetimes, ie. the forestry and agriculture projects?

I actually think those are among the ones that are the most worth pursuing. Right now I see one titanic obstacle to climate change mitigation, and that is the United States (US) government. If the US government were leading the charge, then everyone else would be in its slipstream and we would have this problem solved. In the US, the agricultural sector is incredibly powerful. On the issue of climate change, farm state senators need to see something that will be of value to their constituents, and that is where agricultural soils really come to the fore. If we can convince a few representatives from a few states that this is in the interest of their constituents, it could help tip the debate in the US.

I personally think nuclear is a non-starter. In the article we were not trying to choose sides, only to point out the mitigation technologies that are already in place. However, I cannot imagine that in this era of concerns about terrorism that we are going to start the production of fissionable material all over the world. It is disingenuous when the Bush administration says that the way to solve this problem is through coal and nuclear. Clean coal through carbon capture is fine if it can be made to work. But if you actually injected all of the CO2 produced in the United States (1.5 billion tonnes) the entire country would jack up in the air by 1mm/year. You don't have to be a scientist to know that is not sustainable. If you try to solve even one wedge of this problem with nuclear, it would require a doubling in the amount of nuclear power deployed. Solving the problem entirely with nuclear means increasing deployment by a factor of 10, and if you calculate how many of these plants would have to be in countries like Sudan and Afghanistan, you are just not going to do it.

Why did you choose the goal of stabilization at 500ppm?
*current atmospheric concentration of CO2 is 380ppm

What I know from my work on climate modeling is that the earth's system has positive feedback, which mean that if you change anything in your model, the results on the climate system become completely unpredictable. Whenever you are dealing with a system with positive feedback, especially when you live in the system, it is very dangerous to push it around. I think the reason that so many scientists are concerned about climate change is specifically because they don't understand it.

CO2 is dangerous, and I would like to see it reigned in at the lowest possible level. Choosing 350ppm is impractical because we have already passed it. There is a big debate between 450 and 550ppm, the green corporations talk about 550ppm and the green NGOs talk about 450ppm. However, I don't know enough to discriminate between the two in any hard terms. No one knows what difference 50ppm makes so if you say 500 +/- 50 you are able to split the difference.

How does 500ppm goal fit in with the 60% reduction goal by 2050 that the Intergovernmental Panel on Climate Change (IPCC) suggests and that the UK government has committed to?

Very roughly in order to stabilize atmospheric concentrations at 500ppm we have to cap global emissions over the next 50 years at current levels. Given that the developing world is growing at a furious pace, emissions from industrialized countries are going to have to decrease. So if you take the last 30 years of economic growth in developed and developing countries and forecast it into the future, in order to cap atmospheric concentrations, you roughly have to reduce emissions in the developed world 50-60% on 1990 levels.

In order to achieve the 7 wedges, and stabilization at 500ppm, how much will require regulation, and how much can be accomplished through voluntary measures?

If oil prices were to stay at historic levels, then implementing all of the wedges would require regulatory action. However if oil prices continue to rise, and demand from China continues to grow, then we are likely to see a widening of the gap between emissions and GDP growth (as took place during the energy crisis in the 1970s), and a substantial fraction of the efficiency will be paid for by increased prices.

How did the idea for this research originate?

We came to this understanding by working with people from the different facets of the problem, and it became really obvious that we lacked the intellectual capital on solutions to the problem. The work that the Intergovernmental Panel on Climate Change (IPCC) is doing with their integrated assessments is very important. But the problem is that they are so integrated that it is really difficult for a skeptic to become convinced by them. What we need are some simple typologies so it becomes easy for people to envision a solution.

If you can just give people the zero order knowledge in each of the areas that they need - on the science, the technology, the economics, and the policy - then people will begin to see that we can solve this problem. Instead of being uneasy about it they will be able to envision solutions, and once they start envisioning solutions, especially if you are a competitive person, it is energizing, and you want to do something.

Wedge 1

Wedge 2

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