Negotiating an international agreement to fight climate change is hard enough. But for the past several years, scientists have warned that verifying whether countries meet their pledges to cut greenhouse gas emissions could be even harder.
Current U.N. rules require countries to submit national emissions inventories. But the data are self-reported and not required annually from all countries, and there is not always independent information to verify it.
The issue, politically sensitive for many nations, was a bone of contention for the United States and China at U.N. climate talks last year in Cancun, Mexico, although negotiators eventually agreed to develop a global monitoring system.
Now a new government-funded study suggests researchers are getting closer to being able to independently verify an individual nation's CO2 output.
Researchers at Harvard University, the University of Utah and the National Center for Atmospheric Research say they were able to accurately measure carbon dioxide emitted in Salt Lake City using ground stations, weather and land-use data, and a computer model.
Information on the amount of carbon dioxide in the air came from a network of sensors that has kept tabs on Salt Lake City since 2002 with stations placed throughout the metro area, including one on top of a mountain in nearby Snowbird.
The scientists fed information about Salt Lake City's estimated CO2 emissions and local weather conditions into a model that simulated how atmospheric conditions would mix and distribute the gas. Then they compared the model results with the observations from the CO2 sensor network.
Their results, published this week in the Proceedings of the National Academy of Sciences, show the model estimates came within 15 percent -- or less -- of Salt Lake's actual CO2 emissions.
Going from the country to cities
"The take-home message is that the technology is not the limiting step in terms of acquiring this information," said study co-author Jim Ehleringer, an urban ecologist at the University of Utah. "Cities or countries have the capacity to describe their emissions in a very quantitative and testable way."
The new study's 15 percent margin of error is higher than the 5 percent called for by the National Academy of Sciences in a recent report. But Ehleringer said the work is an important step toward developing an international system that can track CO2 emissions country by country.
Although scientists have measured atmospheric CO2 levels for decades, the current network of ground stations, observatories, aircraft and other instruments emerged during an era when researchers were trying to answer questions about the total amount of carbon dioxide in the atmosphere.
The best way to do that was placing monitoring equipment far from population centers, where CO2 streaming from power plants, automobiles and other infrastructure could skew attempts to determine the average global level of CO2.
But these days, with many scientists are focused on tracking greenhouse gases produced by human activities at national, regional and local scales, the current monitoring network doesn't measure up.
A satellite measure for outliers?
Now the race is on to create a system that could aid the enforcement of a new climate treaty. Doing so should be a priority for the world's governments, science academies from 15 countries said last week.
"The ability to accurately estimate greenhouse gas sources and sinks is a prerequisite for international agreements or national emission reduction programs to be effective," the academies said in a joint statement.
But while the new study suggests there's a way to improve monitoring of CO2 emissions, there's not always a will.