Tracking the Carbon Footprints of Megacities - They're Watching the Skies in LA

Cities are a major contributor to global anthropogenic greenhouse gas emissions, and increasingly policy is targeting the transportation sector as a means of curbing these emissions.  But the practice of determining exactly how much carbon dioxide, methane, carbon monoxide, and other greenhouse gasses (GHG) are being emitted is still primitive.

 The Megacities Carbon Project aims to change that, using the latest scientific advances in atmospheric monitoring to discover what's really in the air.  Doing so will allow cities to accurately determine if, and how, well their policies are working to curb global warming.




Of the many goals pursued by urban transportation policy, addressing climate change has recently become a major priority.  Rising global atmospheric levels of carbon dioxide recently peaked past 400 parts per million, and the trend shows no sign of stopping.  Cities are increasingly taking on a role as policy leaders in this domain, as many national government (especially the United States) have been slow to act.  Cities are also a natural focus for carbon-reduction plans, as they are the single largest contributor to greenhouse gas (GHG) emissions.  Depending on how power plants are accounted for, cities are responsible for between 50% and 70% of all anthropogenic GHG emissions.  This is despite the fact that cities generally have less emissions on a per-capita basis. Transportation is a large contributor to these emissions, and as such many cities have developed GHG policy and reduction goals that explicitly focus on the transportation sector.

Any policy initiative aimed at reducing GHG emissions (usually Carbon Dioxide, or CO2) is a step in the right direction, but the truth is that our understanding of urban GHG emissions is still very limited.   A sparse network of monitoring stations measures ambient levels of GHG in the pristine atmosphere, such as the station in Hawaii that recorded the record 400 ppm.  And although the chemical relationships that create them are well defined, the story of how GHG end up in the air is complicated by the complexities of atmospheric dynamics and actual emission patterns.

But wait, you may be saying, I hear about carbon footprints all the time.  Metro, for instance, tells us that the Portland region is responsible for 31 million metric tons of CO2 equivalent, 25% of which is from non-freight transportation. CO2 equivalent accounts for the atmospheric fate of all greenhouse gas emissions, including methane and carbon monoxide, and converts them to the amount of CO2 that has similar "global warming potential." These GHG inventories are generated from "bottom-up" energy accounting.  Though helpful for characterizing the impacts of a city on a broad scale, they don't provide the spatial or temporal resolution to provide detailed feedback for policy evaluation.  Additionally, the uncertainties in these (often annual) inventories can be quite large.

The Megacities Carbon Project, is working toward detailed, directly measured, global monitoring of GHG emissions.  Organized by NASA's Jet Propulsion Laboratory (JPL), the project aims to learn how megacities (over 10 million population) emit and distribute greenhouse gasses.  Pilots are underway in Los Angeles and Paris. Using satellites, aircraft fly-bys, high-elevation scanner installations, building mounted monitors, and mobile vans, the project is gathering information on emissions and atmospheric dynamics at scales ranging from street-level to continental.  In Los Angeles, a monitor atop Mt. Wilson scans the city every few minutes from desert to ocean, measuring GHG levels at approximately two dozen points.  In Paris, a similar monitor is mounted atop the Eiffel Tower.

Although the program has been operating for almost a year, the full monitoring network is not yet deployed and calibrated.  Once it is, the data sets will be released online for anyone to use at will.  The program researchers say they expect the data to be valuable to independently verify how well the cities are doing in their lofty carbon reduction goals.  Los Angeles, in the Green LA Plan, is trying to reduce their emissions by 35% from 1990 levels in 2030.  Paris is aiming for a 25% reduction (vs. 2004) by 2020.  Although there are many challenges yet to be overcome, researchers are optimistic about the program's potential.  It will help to increase understanding of urban atmospheric behavior and will begin to create a link between the basic science and an operational monitoring framework that can inform policy.  Who knows, perhaps by next year we will know exactly how much carbon CicLAvia kept out of LA's skies.

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JPL Mega Cities Carbon Project:
http://megacities.jpl.nasa.gov

Cities' contribution to global warming: notes on the allocation of greenhouse gas emissions:
Environment and Urbanization October 2008 vol. 20 no. 2 539-549
http://eau.sagepub.com/content/20/2/539

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Thanks to Brett Lezon for editorial assistance.