In a new article in the Proceedings of the National Academy of Sciences, Duke University scientists Robert B. Jackson and William H. Schlesinger calculate what it would take to reduce American carbon dioxide output by 10%, comparing established carbon sequestration methods with efficiency improvements in transportation. They found that sequestration was less effective than anticipated, and vehicle efficiency increases proved a much better option. The article itself is behind a subscriber-only wall, but the abstract is available, as is a detailed news release from Duke and an article in Nature News. While their calculations are interesting, I think they're missing the bigger picture.
Jackson and Schlesinger look at carbon sequestration methods such as no-till agriculture, cropland retirement, and actively planting forests. While these don't have the experimental pizzaz of sequestration methods like direct geological injection of CO2, deep-ocean burial, or genetic engineering of plants to enhance carbon absorption (PDF), they have the distinct advantage of being presently-available and well-understood methods. Unfortunately, the advantage they don't have is utility: even aggressive use of no-till agriculture and cropland retirement would net only a 4% improvement in CO2 emissions; in order to reduce carbon output by 10%, Jackson and Schlesinger calculate that the United States would have to convert one-third of its croplands to carbon-storing forest plantations. While the idea of millions of acres of additional trees has some visceral appeal, the economic and social damage from the loss of so much agricultural land would be severe.
The 10% reduction in CO2 output could be much more readily achieved, Jackson and Schlesinger argue, via significant improvements in vehicle efficiency. They assert -- and here I really wish I could look at the original article, because I'd like to see the details of the argument -- that the US vehicle fleet fuel efficiency could be doubled with off-the-shelf technology. A doubling of efficiency would achieve the 10% reduction, as vehicle emissions currently make up 20% of total US CO2 output.
I have no doubt that improvements in vehicle efficiency are desperately needed; the recent California Air Resources Board decision to require a 25% reduction in vehicle CO2 output by 2009 and 34% by 2016 is a good step in that direction. However, an across-the-board cut of 50% with current technology just doesn't sound plausible to me, especially given that even the Union of Concerned Scientists -- hardly a bastion of fossil fuel enthusiasts -- argues that a 40-43% reduction would be achievable with the use of near-term advanced (not yet on the shelf) technologies. Both CARB and UCS suggest that current technology could produce a 25% reduction -- impressive, to be sure, but nowhere near enough to cut overall emissions by 10%.
There is also the question of whether there are other areas where significant short-term improvements in efficiency could have big CO2 reduction payoffs. Residential energy use is a likely candidate. In 2003, CO2 emissions from residential energy consumption in the US (see slide 14) amounted to 1,220 million metric tons, or about 21% of US energy-related carbon dioxide output, a figure that's roughly equivalent to what Jackson and Schlesinger's give as CO2 emissions from cars and light trucks. Many residences are woefully energy inefficient, with poor insulation, older appliances, drafty windows, and the like. The Rocky Mountain Institute estimates that most homes could easily be made up to 60% more energy efficient. It's surprising what can make a difference -- as we noted here in April, homes in warmer parts of the country can cut air conditioning use by up to 40% simply by painting their roofs white.
Jackson and Schlesinger's article supports the argument that significant emission cuts are possible with the right application of policy and technology, but it doesn't go far enough. We need to see a comprehensive study which looks at all of the anthrogenic sources of carbon dioxide emissions, from vehicles to energy production to industrial pollution, and compares the various mitigation possibilities. Such a study should look at technologies and techniques (such as alternative energy systems, building design, sequestration, etc.) that are both currently-available and still-experimental. The information is out there, scattered across myriad think tanks and government agencies -- we just need someone to put it all together. Any volunteers?
covers the vehicle stuff pretty thoroughly.
Look at the supply curve in there - nice chart of "equivalent price per barrel" and "number of barrels which could potentially be saved" - so you can say "for $15 a barrel, we could save 2m barrels a day" or whatever the actual figure it.
We need a chart like that for CO2 savings!
There is a very interesting article in Science, by Pacala and Socolow from Princeton, about this topic. It's also worth reading:
Stabilization Wedges: Solving the Climate Problem for the Next 50 Years with Current Technologies. S. Pacala and R. Socolow, Science 13 August 2004; 305: 968-972 [DOI: 10.1126/science.1100103]