Could UN climate pact work? This is one way we'd actually know.

From southern California's Mt. Wilson to San Clemente Island off of the coast, scientists have stitched together a network of regional sensors to help answer a key question arising from the new United Nations climate agreement:

How can we independently measure greenhouse gas emissions to help countries transparently meet their reduction goals?

The network is part of the Megacities Carbon Project – a pilot effort to audit greenhouse-gas emissions using satellites, aircraft, and ground-based sensors. The goal is not to police and punish. Instead, the system is designed to help see if carbon-emission control efforts are working and, if not, where efforts need to be strengthened.

Independent verification as a punitive activity in climate agreements “is a thing of the past. We're no longer trying to do a gotcha,” says Riley Duren, one of five United States researchers leading the Megacities Carbon Project, which is operating in Los Angeles, Paris, and Sao Paulo.

In Los Angeles, the effort has been running full time for about two years and already is meeting with success. For instance, a key sensor on Mt. Wilson has shown that methane emissions in Los Angeles range from 18 to 61 percent higher than the state Air Resources Board had estimated. The board has since adjusted its estimate, says Mr. Duren, who also is the chief systems engineer for the Earth Sciences Directorate at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, Calif.

The Megacities Carbon Project is one of about 16 urban greenhouse-gas monitoring experiments underway around the world. These efforts have varying degrees of maturity, says Duren. The ultimate goal, however, is to weave them into a broader, expandable network that develops common tools and techniques others can adopt.

The project also is crafting ways to share measurements in an open, transparent way. That is consistent with Article 13 of the climate pact reached in France last weekend, which among other elements, calls for nations to report emissions and update their progress "in order to buld mutual trust and confidence and to promote effective implementation."

The article represents “a significant step forward” compared with the 1997 Kyoto Protocol, according to Jennifer Morgan, who heads the climate program at the World Resources Institute, an environmental think tank in Washington.

The need is highlighted by China's recent acknowledgement that it had underreported its carbon dioxide (CO2) emissions from burning coal by 17 percent, notes Mavendra Dubey, a climate researcher at Los Alamos National Laboratory.

The Megacities Carbon Project is focusing on the globe's larger cities – those with a population of at least 10 million – because megacities are the sources for about 70 percent of greenhouse-gas emissions from burning fossil fuels and other human activities. Moreover, cities, as well as states and provinces, have become increasingly active in setting out plans to curb emissions. This makes them ideal laboratories for projects that monitor emissions for diagnostic reasons, rather than punitive ones.

In Los Angeles, project researchers are tracking emissions using sensors located at 13 sites throughout the Los Angeles basin and in a handful of locations outside the basin. The sensor on Mt. Wilson is a prototype that, in a smaller version, could be installed on large satellites that constantly have the same hemisphere of Earth in view. The researchers also use data from instrument-bearing aircraft as well as from NASA's Orbiting Carbon Observatory 2 satellite and Japan's GOSAT, which also measures greenhouse gases.

Other technologies could help. For instance, scientists have turned to virtual supercomputers on the cloud to process vast amounts of remote-sensing data. The cost is a pittance compared with owning, maintaining, and upgrading stand-alone supercomputers.

“Until now, if you wanted to do very large-scale climate science, you'd pretty much have to be a national government with control of a national lab with some giant gold-plated supercomputers,” says Steve Brumby, chief technology officer for Descarte Labs, a year-old commercial startup that specializes in analyzing remote-sensing data.

In less than a day of cloud supercomputing, for example, Descarte Labs converted LANDSAT satellite images NASA has accumulated since 1972
and stored on the cloud into a coherent sequence of scenes. The sequence could be used for more detailed, continuously updated analyses of trends
in corn production in the US, urban sprawl, or shifts in vegetation that would affect the global carbon cycle.

At least initially, some countries might not welcome aircraft overflights or the installation of ground-based sensors, researchers acknowledge. That's a sensitivity that must be respected, the new climate agreement acknowledges. In those cases, satellite data may be the best approach for tracking progress while allowing those countries to gain confidence in the nonpunitive nature of the independent data-collecting efforts.

Meanwhile, the World Meteorological Organization has been working on a draft proposal to set up a system to gather and distribute data from greenhouse-gas monitoring efforts.

“The good news is that everybody agrees that climate change is a problem,” says Los Alamos’s Dr. Dubey. “Now we have to verify and monitor – not punitive, but to build capacity and evidence that we're moving in the right direction.”

A global monitoring network, he says, “certified and bought by the world, with common methods, would be ideal.”