
Carbon Dioxide and Climate Change
Related to the image of the world at night is the point sources of carbon dioxide emissions. Note that the locations are mostly in the developed nations with a strong presence from China and India.

The bulk of our energy-related pollution comes from electricity generation and transportation. For example look at the U.S. data.

Overall, we still expect to see carbon dioxide levels decreasing for the US in the short term. Hot summers (lots of air condensation), cold winters, and world economic productivity will influence emissions. Of issue is whether carbon dioxide sequestration will have a role to play in reducing the rate of growth of CO2 in the atmosphere in the future (perhaps). Fuel switching is the leading contributer to this reduction (shale gas replacing coal), but as we have seen, much of the international growth in electricity is likely to come from the cheapest, available source: coal.

Some nations have already enacted policies that have resulted in carbon dioxide emission reductions. Below is the artistic representation of the Sleipner natural gas platform in the North Sea off the coast of Norway. The rig is extracting natural gas, but like other natural gas wells, will also contain carbon dioxide. Separating and releasing the carbon dioxide is common, however, a carbon tax in Norway makes this expensive. Thus, they sequester the carbon dioxide in a deep saline aquifer under the ocean but above the gas field. With >10 years of experience >10 million toms of carbon dioxide have been stored. This is one of the few large-scale sequestration sites currently in operation. To put this in perspective: a 500 MW coal-fired power plant will generate nearly 4 million tons of CO2 per year.

There are a variety of large-scale point sources of carbon dioxide that could provide an opportunity for sequestration (or in the terminology of the day: carbon capture and storage). These could be electric utilities, cement manufacturing, refineries, ethanol production facilities, and others. If you would like more information on geologic sequestration see the Geologic Sequestration Atlas. The image below shows large-scale point sources of carbon dioxide and the location of deep saline aquifers as well as oil and natural gas fields, and coal basins (some of the coal being too deep to mine and a potential sequestration site). Generally, we have good location citing between sources and sinks. Yet it is unclear how significant a role CCS will be in the future. It will not be enough by itself, to reduce carbon dioxide emissions back to previous levels.


For a look at how the U.S. might meet reduction goals (we are not sure what these reduction goals might be, and it will likely be a moving target):
Workers at Princeton suggested a 7 "wedges" strategy to meet 2004 carbon dioxide emission levels (it now seems that many nations will find the Kyoto reductions out of reach). "Very roughly, stabilization at 500 ppm requires that emissions be held near the present level of 7 billion tons of carbon per year (GtC/year) for the next 50 years, even though they are currently on course to more than double." There are 15 options, any 7 of which combined would provide the stabilization. View Introduction to the Wedges from Princeton University for additional information.

The 15 Options
Option 1: Improved fuel economy
Option 2: Reduced reliance on cars. A wedge would also be achieved if the average fuel economy of the 2 billion 2054 cars were 30 mpg, but the annual distance traveled were 5000 miles instead of 10,000 miles.
Option 3: More efficient buildings
Option 4: Improved power plant efficiency. This can be achieved through gasification of coal, oxy-combustion, and other approaches.
Option 5: Substituting natural gas for coalescent from natural gas has fewer CO2 emissions
Option 6: Storage of carbon captured in power plants
Option 7: Storage of carbon captured in hydrogen plants
Option 8: Storage of carbon captured in synfuels plants (carbon capture and storage)
Option 9: Nuclear fission
Option 10: Wind electricity
Option 11: Photovoltaic electricity
Option 12: Renewable hydrogen
Option 13: Biofuels
Option 14: Forest management
Option 15: Agricultural soils management. This is essentially terrestrial carbon capture, increased carbon in the soil.
None of these are easy fixes, each is a grand challenge alone. Together 7 of these will be a grand, grand challenge!
The full paper is: Pacala, S.; Socolow, R., Stabilization wedges: Solving the climate problem for the next 50 years with current technologies. Science 2004, 305 (5686), 968-972.
A word on the Kyoto Protocol. After Australia ratified the protocol in 2008, the U.S. stands alone as a participant who has signed but not ratified the Protocol. The Protocol became active in 2005 when the necessary number of participants (covering a certain percentage of the greenhouse gas emissions) had ratified it. How we move forward is not necessarily tied to the Kyoto Protocol. It will certainly be interesting to see how far we deal with CO2 and how quickly.
