as the core of a monitoring and verification system. Procedural verification by an independent international body would be supplemented by independent and transparent checks on fossil-fuel combustion and deforestation, which together are responsible for about three-fourths of all UNFCCC greenhouse gas emissions. Targeted research would ultimately lead to improved monitoring and verification of all greenhouse gases.

Realistic near-term goals are to reduce uncertainties of fossil-fuel CO2 emissions to less than 10 percent in annual, national inventories and to provide checks on these emissions, especially from large, high-emitting countries—such as the United States, China, or India—using independent methods that are equally accurate. Although national inventories of AFOLU emissions are currently relatively inaccurate, a realistic near-term goal is to reduce uncertainties of AFOLU CO2 emissions and to be able to estimate remotely the most important activities that cause these emissions (deforestation, afforestation, and forest degradation) with <10 percent uncertainty. In contrast, fundamental research is needed before it will be possible to estimate national emissions of N2O, CH4, and the synthetic fluorinated gases with reasonable accuracy using independent methods. The need for fundamental research is especially evident in the high uncertainties for emissions of CH4 and N2O from all important AFOLU sources, even for estimates from improved inventory methods.

In addition to improving estimates of AFOLU emissions, the satellite surveys and inventory improvements recommended in this report would allow monitoring of individual projects aimed at creating carbon sinks to offset emissions. The ecosystem inventories would provide the baselines against which an offset project could demonstrate its effect on carbon uptake, which is necessary because carbon fluxes to and from ecosystems fluctuate with the weather and other factors. They would also provide a means for monitoring natural sinks and sources on unmanaged land.

An additional benefit of the proposed expansion of the system to monitor greenhouse gases is that it would enhance our ability to monitor and study natural carbon sinks on land and in the oceans. The natural sinks are not counted in UNFCCC inventories, but they currently absorb about half of greenhouse gas emissions (approximately evenly divided between land and oceans). Because they are so large, changes in the natural sinks could weaken the impact of a treaty. The proposed additions to atmospheric sampling, inventories, and tracer-transport inversion would significantly improve our ability to monitor and study the natural sinks.

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