When it comes to monitoring carbon dioxide in the atmosphere, a key element of any coherent strategy to reduce emissions, there are things we know and things we don’t know. Ground-based monitoring stations in places like Antarctica and Hawaii give a good picture of the overall levels of CO2 in the air.
It’s more difficult, however, to determine precisely where the increasing carbon dioxide levels are coming from. This will become more important in the effort to see if countries are living up to their commitments made at COP21.
At present, the process depends on self-reporting. Each country rolls up their best estimates of how much carbon they emitted, based on how much fuel was sold and presumably burned. This is difficult to reconcile with the ground-based concentration measurements, because the amount of carbon absorbed by the oceans and forests must be factored in.
This is clearly imperfect considering that, for example, last year China admitted to under-reporting the amount of coal it burned by as much as 17 percent.
Better solutions are on their way. Space-based carbon monitoring satellites are already up and running. One U.S. satellite, OCO-2, already orbits the Earth every 99 minutes, as does a Japanese satellite called GOSAT. These satellites are able to more precisely pinpoint emissions from countries, states and even cities. But each of them will only cover a relatively narrow swath of the Earth’s surface.
China expects to launch two more such satellites in the coming months, which will help fill in the coverage area, though full coverage is still a long way off.
Says John O. Niles, executive director of the Carbon Institute: “Space-based monitoring of CO2 is the most powerful reality check against governments self-reporting their CO2 inventories and fluxes.”
A complete system would require at least three satellites in low-Earth orbit and three in geostationary orbit. The European Union proposed such a system under its Copernicus program. This ambitious program will be expensive and will likely face objections by countries that don’t want satellites snooping on them.
In the meantime, more modest programs are helping to fill in the gaps. NASA recently launched a new aircraft-based carbon monitoring system called ACES, which utilizes LIDAR (light detection and ranging) and operates at night, which is helpful, since the satellite-based system operates only in daylight.
Add to this a set of new ground-based laser technologies. One of these, GreenLite, developed by Harris Corp., can measure sources within a city by mounting lasers and reflectors on the rooftops of skyscrapers. This will allow emission sources to be pinpointed precisely. The system can also provide an overall picture of the city’s emissions, said Eric Webster, Harris’ vice president and director of environmental systems, “As you watch the monitor screen throughout the day, you can actually see the city ‘breathe CO2’ as rush hour comes and goes and power plants respond to peaks in demand.”
Harris demonstrated the system in Paris during the COP21 climate talks.
OCO-2 Image courtesy of NASA