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Should the world's nations sign a treaty limiting their climate-altering gas emissions, it would be essential for them to be able to monitor one another's carbon dioxide output.

Such a tool is under development by a University of Utah-led research team, which has shown it can detect changes as small as 15 percent in a region's emissions.

That's a far cry from the 5 percent target recommended by the scientific community, but the findings provide a crucial proof of concept, according to James Ehleringer, a U. biology professor who coauthored a new study demonstrating the method.

"This is the first attempt to assess the degree of confidence we can have in existing models," Ehleringer said. "With improved monitoring we can get to the National Research Council's goal."

Michael Schmidtz, acting executive director of ICLEI: Local Governments for Sustainability, called the new measurement tool "a big step forward."

"Anything that allows for more direct measurements is an important tool," he said.

ICLEl, whose 550 U.S. members are local governments looking for best-practices tools for addressing environmental issues they face, encourages inventories of greenhouse gas emissions. Utah members include Salt Lake City, Park City, Summit County and St. George.

Schmidtz said the inventories and the measurements together strengthen communities in a variety of ways, including helping to cut pollution and save energy costs.

He noted that local governments are often on the front lines when it comes to dealing with the impacts of climate change, such as extreme weather. Last year, there were 14 weather events that logged damages exceeding $53 billion and caused 99 federally designated disasters.

Ehleringer began monitoring greenhouse gas emissions a decade ago when he set up a network of stations around the Salt Lake Valley. The network now yields the world's largest publicly available data set of carbon concentrations in an urban airshed.

For the new study, his team pulled carbon dioxide data from three monitoring stations, at the U., in downtown Salt Lake City and in Murray; from weather stations; and satellite data indicating which areas are covered by homes, trees, agricultural lands and other geographic features.

"The primary motivation for the study was to take high-quality data of atmospheric CO2 in an urban region and ask if you could predict the emissions patterns based on CO2 concentrations in the air," Ehleringer said. "The idea is, can you combine concentration information — CO2 in the air near the ground — and weather patterns, which is wind blowing, and mathematically determine emissions based on that information."

While the tool would put states and nations on notice that their emissions are being measured, Ehleringer also contends that it could wield a "carrot effect."

"If you want to be a 'green city' it provides verification that can help attract investment. It says, 'This is a sustainable feature of our city,' " he said.

Ehleringer's team included Kathryn McKain and Steven Wofsy of Harvard University, and Thomas Nehrkorn and Janusz Eluszkiewicz of Atmospheric and Environmental Research Inc.

The Utah part of the research was funded by the U.S. Department of Energy, while the co-authors were funded by NASA, the National Science Foundation and "the U.S. intelligence community."