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Verifying Greenhouse Gas Emissions: Methods to Support International Climate Agreements Summary The world’s nations are moving toward agreements that will bind us together in an effort to limit future greenhouse gas emissions. With such agreements will come the need for all nations to make accurate estimates of greenhouse gas emissions and to monitor their changes over time. In this context, the National Research Council convened a committee of experts to assess current capabilities for estimating and verifying greenhouse gas emissions and to identify ways to improve these capabilities. This report is focused on the greenhouse gases that result from human activities, have long lifetimes in the atmosphere and thus will change global climate for decades to millennia or more, and are currently included in international agreements. These include carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), hydrofluorocarbons (HFCs), perfluorinated hydrocarbons (PFCs), and sulfur hexafluoride (SF6)—all of which are covered by the United Nations Framework Convention on Climate Change (UNFCCC)—and chlorofluorocarbons (CFCs), which are covered by the Montreal Protocol. The report devotes considerably more space to CO2 than to the other gases because CO2 is the largest single contributor to global climate change and is thus the focus of many mitigation efforts. Only data in the public domain (available to all without restriction or high cost) were considered because public access and transparency are necessary to build trust in a climate treaty. The report concludes that each country could estimate fossil-fuel CO2 emissions accurately enough to support monitoring of a climate treaty (see Table S.1). However, current methods are not sufficiently accurate to check these self-reported estimates against independent data (e.g., remote sensing, atmospheric measurements) or to estimate other greenhouse gas emissions. Strategic investments would, within 5 years, improve reporting of emissions by countries and yield a useful capability for independent verification of greenhouse gas emissions reported by countries. Table S.1 shows that by using improved methods, fossil-fuel CO2 emissions could be estimated by each country and checked using independent information with less than 10 percent uncertainty. The same is true for satellite-based estimates of deforestation, which is the largest source of CO2 emissions next to fossil-fuel use, and for afforestation, which is an important sink for CO2. However, self-reported estimates of N2O, CH4, CFC, HFC, PFC, and SF6 emissions will continue to be relatively uncertain and we will have only a limited ability to check them with independent information. METHODS FOR ESTIMATING GREENHOUSE GAS EMISSIONS The report examines three categories of methods for estimating greenhouse gas emissions: national inventories, atmospheric and oceanic measurements and models, and land-use measurements and models. Under the UNFCCC, countries are required to inventory the human activities that cause greenhouse gas emissions, such as fossil-fuel consumption or forestry, and then multiply each activity level by its rate of emissions (emission factor). Uncertainties in the self-
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Verifying Greenhouse Gas Emissions: Methods to Support International Climate Agreements TABLE S.1 Current and Near-Term Capabilities for Estimating National Anthropogenic Greenhouse Gas Emissions Gas Major Sectors or Activities Method Current Uncertainty for Annual Emissionsa Possible Improvements in 3-5 Years Uncertainty of Improved Methods CO2 Total anthropogenic UNFCCC inventory 1 (developed countries)b Adopt most accurate methods in all countries 1 CO2 Fossil-fuel combustion UNFCCC inventory 1-2 (developed countries) Adopt most accurate methods in all countries 1 CO2 Fossil-fuel combustion Atmospheric measurements and models 4-5 Develop improved tracer-transport inversion through new observations (14CO2, additional ground stations, Orbiting Carbon Observatory [OCO] replacement) and data assimilation 1-3 (annual) 1-2 (decadal change) CO2 Large local sources (e.g., cities, power plants) Atmospheric measurements and models 5 Develop and deploy a CO2 satellite program, including an OCO replacement, new in situ measurements in cities, and a research program to guide network design and satellite validation 2 (annual) 1 (decadal change) CO2 Agriculture, forestry, and other land-use (AFOLU) net emissions UNFCCC inventory 1-4 (developed countries) Adopt most accurate methods and activity data; improved emission factors through research and comprehensive ecosystem inventories 1-3 CO2 AFOLU Atmospheric measurements and models 5 Develop improved tracer-transport inversion through new satellite and in situ observations 4-5 CO2 AFOLU Land-use measurements and models 2-4 Develop improved observations, data assimilation, and models with ecosystem research 2-3 CO2 Deforestation and degradation source, afforestation sink Land-use measurements and models 2-4 (forest area change) 3-4 (emissions) Develop improved observations, Landsat continuity, data assimilation, and models with ecosystem research 1-2 (forest area change) 2 (emissions) CH4 Total anthropogenic UNFCCC inventory 2-3 (developed countries) Adopt most accurate methods and activity data and improved emission factors through research 1-3 CH4 Total anthropogenic Atmospheric measurements and models 3-5 Develop improved tracer-transport models, new satellite and in situ observations, and improved emission models through research 2-3 CH4 Energy, industrial processes, and waste UNFCCC inventory 1-5 (developed countries) Adopt most accurate methods and activity data and improved emission factors through research 1-2 CH4 AFOLU UNFCCC inventory 2-4 (developed countries) Adopt most accurate methods and activity data and improved emission factors through research 2-3 N2O Total anthropogenic UNFCCC inventory 2-5 (developed countries) Adopt most accurate methods and activity data and improved emission factors through research 2-4 N2O Total anthropogenic Atmospheric measurements and models 4-5 Develop improved tracer-transport and emission models, additional observations 3-5 N2O Energy and industrial processes UNFCCC inventory 3-5 (developed countries) Adopt most accurate methods and activity data and improved emission factors through research 3-4 N2O AFOLU UNFCCC inventory 2-5 (developed countries) Adopt most accurate methods and activity data and improved emission factors through research 2-4 CFCs, PFCs, HFCs, and SF6 Industrial processes UNFCCC inventory 1-4 (developed countries) Adopt most accurate methods in all countries 1-3
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Verifying Greenhouse Gas Emissions: Methods to Support International Climate Agreements Gas Major Sectors or Activities Method Current Uncertainty for Annual Emissionsa Possible Improvements in 3-5 Years Uncertainty of Improved Methods CFCs, PFCs, HFCs, and SF6 Industrial processes Atmospheric measurements and models 4-5 Develop gridded inventories, improved tracer-transport inversion, and measurement of correlated variations of gases 2-5 NOTES: 1 = <10% uncertainty; 2 = 10-25%; 3 = 25-50%; 4 = 50-100%; 5 = >100% (i.e., cannot be certain if it is a source or sink). Ranges represent emission uncertainties in different countries (e.g., 1-3 means that uncertainties are <10% in some countries, 10-25% in some, and 25-50% in others). Uncertainty levels correspond to two standard deviations. Shaded rows are the self-reported values; unshaded rows are the independent checks on the self-reported values from independent methods. aUncertainties for the magnitudes of decadal changes in national emissions can be computed from the numbers in the table using standard statistical methods. Decadal changes (the cumulative change in emissions over 10 years) are reported in the rows requiring OCO measurements because early estimation biases will be reduced in calculation of a decadal change. The uncertainty of a trend is reported as a percentage of the emissions at the beginning of the decade. bBased on 2006 data reported by five developed countries (Denmark, Greece, Portugal, the United States, and Poland) with a range of institutional capabilities for compiling inventories. In countries where AFOLU sources dominate energy and industrial sources, the uncertainties for total anthropogenic emissions would be much higher. reported national inventories depend on the data and methods used to create them, which in turn depend on each country’s institutional and technical capabilities. In many developed countries, uncertainties are reported to be less than 5 percent for national CO2 emissions from fossil-fuel use (Table S.1), which is the dominant source. With the exception of a few minor sources in the industrial sector, uncertainties are much higher for other greenhouse gases and sources and vary greatly by country. Uncertainties for the net CO2 emissions from agriculture, forestry, and other land uses and for emissions of CH4, N2O, PFCs, HFCs, CFCs, and SF6 from all sectors can be less than 25 percent in some countries and greater than 100 percent in others. The second method for estimating greenhouse gas emissions, called tracer-transport inversion, is based on atmospheric and/or oceanic measurements of the gases and mathematical models of air and water flow. Tracer-transport inversion estimates the net sum of anthropogenic and natural sources and sinks. Uncertainties inferred from tracer-transport inversions are less than 10 percent for the net global CO2 flux to the atmosphere but greater than 100 percent for anthropogenic CO2 fluxes at national scales (Table S.1). These large uncertainties arise because of the small size of the anthropogenic signal relative to the large and uncertain natural cycles of emissions and uptake, errors in the reconstruction of atmospheric transport, and the paucity and limited distribution of observations. Tracer-transport estimates of emissions of N2O, CH4, and the synthetic fluorinated gases are currently too uncertain to verify national emissions. The third method estimates emissions of CO2, CH4, and N2O using methods that are conceptually similar to those used for UNFCCC inventories, but can be made using independent information on land cover. It can be used to estimate emissions from both natural sources and land-use activities, such as agriculture and forestry. Satellite imagery provides the remote information on land surface characteristics and change. This information is converted into estimates of emissions using biogeochemical models constrained by measurements of greenhouse gas exchange between the land and the atmosphere. Satellite imagery is particularly useful for constraining forestry activities and can be used to determine the area of deforestation and forest degradation. The total annual change in forest area has an uncertainty of 10-25 percent in northern forests and up to 100 percent in tropical forests (Table S.1). Uncertainties in emissions from deforestation, reforestation, and forest degradation are high for both annual values and trends, ranging from 25 to 100 percent, because of uncertainties in parameters used to translate deforested area into CO2 emissions. Land remote sensing can also be used to estimate agricultural emissions by identifying the areas using certain agricultural practices, such as paddy rice. Annual uncertainties in CH4 emissions from rice production are 25-50 percent, and uncertainties in N2O emissions from synthetic fertilizer use and manure production are 50-100 percent.
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Verifying Greenhouse Gas Emissions: Methods to Support International Climate Agreements FIGURE S.1 Global anthropogenic greenhouse gas emissions and activities covered by the UNFCCC for 2004. These gases include CO2, CH4, and N2O, as well as HFCs, PFCs, and SF6 (the F-gases). The emissions of each gas are weighted by its 100-year global warming potential. Note that including short-lived greenhouse agents (e.g., ozone precursors) or decreasing the time horizon over which the global warming potential is calculated will decrease the fractional importance of fossil-fuel CO2. SOURCE: Figure 1.1b from IPCC (2007b), Cambridge University Press. Although uncertainties in emissions estimates are high overall, it may not be necessary to obtain accurate measurements of all greenhouse gases to support treaty monitoring and verification. The majority of anthropogenic greenhouse gas emissions covered by the UNFCCC are in the form of CO2, primarily from fossil-fuel use (~74 percent in 2004; Figure S.1) and secondarily from deforestation (estimates range from 12 to 22 percent), making these two activities an obvious focus for monitoring. FRAMEWORK FOR ESTIMATING AND VERIFYING GREENHOUSE GAS EMISSIONS The UNFCCC framework for reporting national emissions comprises three main elements: An internationally negotiated and accepted capability to monitor national, anthropogenic emissions of the most important greenhouse gases, Independent review by an international body to determine whether appropriate procedures and methods are being used to prepare national inventories, to identify inconsistencies within and between reports, and to take action if problems are uncovered, and An established mechanism through the Intergovernmental Panel on Climate Change (IPCC) to incorporate new information and strengthen inventory methods. Because fossil-fuel CO2 emissions can be estimated with reasonable accuracy using UNFCCC inventory methods (Table S.1) and because of the broad international support for the reporting framework, UNFCCC procedures have been, and will likely continue to be, the primary means for monitoring and verifying greenhouse gas emissions and reductions under a new international climate treaty. However, the current system has shortcomings for this purpose: Developing countries do not provide regular, detailed emissions reports. The availability of independent data against which to check self-reported emissions is limited. Estimates of CO2 emissions from land use, as well as emissions of other greenhouse gases, have uncertainties that are greater than the expected emissions reductions over a treaty’s lifetime. The committee’s recommendations are aimed at overcoming these weaknesses and improving the capability to estimate and verify greenhouse gas emissions in support of a climate treaty. Although some will take many years to implement, most will yield results within a few years. RECOMMENDATIONS The committee’s recommendations fall into three broad categories: (1) strengthening national greenhouse gas inventories, which will likely remain the core of a global monitoring and verification system; (2) improving the ability to independently and remotely estimate national, annual fossil-fuel CO2 emissions and to monitor emission trends; and (3) developing the capability to make accurate estimates of national CO2, N2O, and CH4 emissions and CO2 removals from sinks
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Verifying Greenhouse Gas Emissions: Methods to Support International Climate Agreements from agriculture, forestry, and other land uses, and to independently check self-reported estimates of CO2 emissions from deforestation, reforestation, and forest degradation. Strengthened National Greenhouse Gas Inventories The two recommendations below are intended to improve the accuracy of national inventories and facilitate comparison with independent methods. The first recommendation would extend reporting of UNFCCC inventories to every country, and the second would increase the spatial and temporal resolution of emission estimates. Recommendation. UNFCCC parties should strengthen self-reported national emissions inventories by working toward Extending regular, rigorous reporting and review to developing countries, and Extending top-tier (most stringent) IPCC methods to the most important greenhouse gas sources in each country. UNFCCC reporting guidelines differ for developed (Annex I) and developing (non-Annex I) countries. Annex I countries report annual estimates for all anthropogenic sources and sinks of six greenhouse gases (CO2, CH4, N2O, SF6, PFCs, and HFCs) and a time series of annual estimates going back to 1990. In contrast, non-Annex I countries are required to produce only a periodic inventory of CO2, CH4, and N2O at the sector (i.e., energy; industrial processes and product use; agriculture, forestry, and other land use; waste) level, without a detailed source breakdown. Most developing countries have produced only one national inventory to date. Financial and technical assistance will be required for developing countries to build an ongoing capacity to collect, analyze, and report emissions information regularly. Significant improvements in national inventories from 10 of the largest emitting developing countries (e.g., China, India) could be achieved at relatively modest cost (about $11 million over 5 years). Countries choose among three tiers of methods for calculating emissions and removals of greenhouse gases. The lowest-tier methods (Tier 1) are simple and use default values for emission factors. Tier 2 methods are similar but use country-specific emission factors and other data, and Tier 3 methods incorporate complex approaches and models of emission sources. Universal application of top-tier methods would significantly reduce uncertainties in reported emissions but would also significantly increase costs. Thus, at a minimum, top-tier methods should be used for the most important greenhouse gas sources in each country. Recommendation. Annex I countries should develop and implement standardized methods for preparing and publishing inventories that are gridded at spatial and temporal resolutions appropriate for the particular greenhouse gas and source. Because the atmosphere is not well mixed at country scales, spatially and temporally heterogeneous emissions imply complex variations in the greenhouse gas abundances both at the surface and in the atmospheric column. Independent estimates of national emissions based on tracer-transport models require some prior knowledge of the pattern of emissions. Many Annex I countries are compiling spatially and temporally resolved greenhouse gas emissions, but a standard method for producing gridded measurements does not yet exist. Gridded inventories would provide information at spatial and temporal scales better matched to the dynamics of the atmosphere and thus facilitate comparisons of reported emissions with atmospheric methods. They would be particularly useful for checking reported HFC, PFC, CFC, SF6, and fossil-fuel CO2 emissions. The optimal sampling scheme will vary among emissions sources and greenhouse gases and must balance cost and complexity against value. Independent Estimation of Fossil-Fuel CO2 Emissions Independent verification of the self-reported fossil-fuel CO2 emissions of individual countries will require additional atmospheric measurements and improved tracer-transport estimates of emissions. The density and coverage of measurements would be improved (1) by establishing new stations near cities and other large local sources and in sparsely sampled regions and (2)
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Verifying Greenhouse Gas Emissions: Methods to Support International Climate Agreements by deploying a CO2-sensing satellite. Measurements of radiocarbon (14C) would enable fossil-fuel CO2 emissions to be separated from non-fossil-fuel sources and sinks. Together, the new measurements and the gridded inventory estimates in Annex I countries would provide the information necessary to reduce errors in the transport models and to overcome the noise from the natural variability of the biosphere. Information derived from all sources could be synthesized in a data assimilation system to produce accurate estimates of anthropogenic CO2 emissions and trends at national scales. The three recommendations that follow represent critical components of this larger effort that could be deployed within 3 years. Recommendation. The National Aeronautics and Space Administration (NASA) should build and launch a replacement for the Orbiting Carbon Observatory (OCO). Most fossil-fuel emissions emanate from large local sources such as cities and power plants. These large sources increase the local CO2 abundance in the atmosphere by 1-10 parts per million (ppm), a signal that is significantly larger than the signal from natural sources and sinks. NASA’s Orbiting Carbon Observatory, which failed on launch in February 2009, would have had the high precision (1-2 ppm) and small sampling area (1.29 × 2.25 km) needed to monitor these large local sources and to attribute their CO2 emissions to individual countries. No other satellite has its critical combination of high precision, small footprint, readiness, density of cloud-free measurements, and ability to sense CO2 near the Earth’s surface. The OCO was designed to study natural CO2 sources and sinks. It would have demonstrated the technology for estimating CO2 emissions from space but would have had two limitations for a climate treaty. First, with a revisit period of 16 days, it would have sampled only 7-12 percent of the land surface, enabling only a small percentage of large local emissions sources to be monitored. Second, it would have had a 2-year lifetime, providing only baseline data against which to measure future trends. A replacement for OCO launched in the first few years of the coming decade and a subsequent mission at the decade’s end should be able to determine if trends in the number and average intensity of CO2 “domes” over a country’s cities and power plants are consistent with reported fossil-fuel emissions. A replacement mission is expected to cost about the same as the original, $278 million. Recommendation. Extend the international atmospheric sampling network: To research the atmospheric domes of greenhouse gases over a representative sample of large local emitters, such as cities and power plants, and To fill in underrepresented regions globally, thereby improving national sampling of regional greenhouse gas emissions. The atmospheric sampling network, coordinated by the World Meteorological Organization’s Global Atmospheric Watch (GAW) and operated by the National Oceanic and Atmospheric Administration (NOAA) and agencies in other countries, comprises approximately 150 stations around the world that measure a host of greenhouse gases from the ground, ocean surface, and air. The stations in the network were purposely located away from large local emitters to minimize contaminating the signal from natural sources and sinks with the signal from fossil-fuel combustion. However, adding ground stations or aircraft to measure emissions from power plants and cities would enable the network to monitor both types of signals. New measurements of relevant trace gases (e.g., greenhouse gases, isotopes of carbon), their biological fluxes, and meteorological variables would be made at locations radiating from the center of each large emitter. This research initiative would yield data needed to calibrate satellite measurements of large local emitters (see previous recommendation), demonstrate an independent capability to monitor large local emitters from ground stations and aircraft, and document long-term shifts in fossil- versus non-fossil-fuel sources in urban and industrial regions. An initial goal could be to deploy instruments at a statistical sample of large emitters (e.g., 5-10 within a research budget of $15 million to $20 million per year) in the United States, but international partners would ideally extend the effort in other countries. The GAW network is capable of achieving the sub-ppm precision in CO2 measurements necessary
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Verifying Greenhouse Gas Emissions: Methods to Support International Climate Agreements to detect the atmospheric signal from widespread but unconcentrated sources, such as land-use fluxes. It also provides an opportunity to make concurrent measurements of other gases that are needed to derive total carbon emissions from a region. However, huge areas of the planet are not adequately sampled by this network. For example, there are only a few sites in Africa and South America. Expanding the GAW network to observe the variations in greenhouse gas abundances in countries with the highest emissions would greatly improve the independent verification of emissions through tracer-transport modeling. Expanding the network to obtain frequent vertical profiles from aircraft and balloons would constrain atmospheric transport and allow more meaningful comparisons with satellite retrievals of column-averaged CO2 than ground-based measurements alone. Negotiators should work toward participation in the cooperative network by all major emitting countries and by groups of neighboring smaller countries. Implementing this recommendation will require financial assistance and capacity building to aid the poorest countries that dominate the most undersampled regions. Recommendation. Extend the capability of the CO2 sampling network to measure atmospheric 14C. Estimating fossil-fuel CO2 emissions from tracer-transport inversion is complicated by poorly understood natural emissions of CO2 that fluctuate and can be as large as or larger than those from fossil-fuel sources. Adding 14C measurements to the atmospheric sampling stations that measure CO2 (CO2 sampling network) would provide an unambiguous means to differentiate between the CO2 from fossil-fuel and non-fossil-fuel sources because modern organic material contains radiocarbon from cosmic rays and bomb tests, but the 14C in fossil fuels has long since decayed away. It would also provide key measurement constraints to improve tracer-transport inversions. The 14CO2 measurements would enable fossil-fuel use to be estimated at subcontinental scales with uncertainties low enough to be useful for verifying self-reported emissions. The 14CO2 measurements could be made at a small incremental cost (~$5 million to $10 million per year for 10,000 measurements, including half in the United States). This initiative could be undertaken by NOAA, which maintains the CO2 sampling network and has the facilities and expertise to collect and process the samples; by the Department of Energy, which operates a suitable accelerator mass spectrometer at Lawrence Livermore National Laboratory; or by another national laboratory or a university capable of making the measurements at the required precision. International partners could help extend this capability to other countries, providing a more global capability for verifying fossil-fuel emissions. Implementation of the recommendations to enhance atmospheric sampling and UNFCCC inventories should lead to rapid improvements in monitoring and verification. Rigorous inventories in all countries, added in situ stations, a replacement for OCO, and the 14CO2 measurements would increase the number of high-resolution greenhouse gas measurements by orders of magnitude, improve transport models, and significantly reduce errors associated with natural emissions. The loss of any one of these measurement systems would increase the uncertainty for tracer-transport inversion, making the uncertainty in the emissions estimates greater than the 10-year reductions likely required under an international treaty. Independent Estimation of Fluxes from Land-Use Sources and Sinks Emissions and removals from land use are highly uncertain both because of uncertainty in the levels of activities such as deforestation or forest planting and because of uncertainty in the emissions per unit of activity. Implementation of the first recommendation below would provide useful estimates of land-use activity levels that could be used to check self-reported values in UNFCCC inventories and also enable more accurate land-use emissions reporting from developing countries. The second recommendation would deliver improved estimates of the emissions per unit of activity. Recommendation. Establish a standing group to produce a global map of land-use and land cover change at least every 2 years. This will require a commitment to maintaining the continuous availability, in the public domain, of Landsat (or an equivalent satellite) and high-resolution satellite imagery.
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Verifying Greenhouse Gas Emissions: Methods to Support International Climate Agreements Landsat imagery provides an independent check on the activities that create the largest CO2 emissions from agriculture, forestry, and other land use. Estimates of global land use and land cover must be made often enough to detect important changes, such as forest clearing or planting (e.g., 1-2 years in most forests). Although individual Landsat scenes are publicly available, regular production of a gridded map of the world would allow country-specific information to be extracted on a routine basis. Such a map would enable countries to validate land-use emissions and would provide a basis for improving land-use inventories in developing countries. The maps could be produced by the U.S. Geological Survey—which has a long history of creating, distributing, and archiving Landsat products—NASA, or a university. For the satellite platforms, either NASA has to keep a successor to the Landsat Data Continuity Mission in its mission queue or another agency will have to maintain the capability. The moderate-resolution (30 m) imagery should be supplemented with statistical samples of high-resolution (1 m) imagery to monitor logging, forest degradation, and certain agricultural practices (e.g., rice cultivation). Such high-resolution data could be obtained either by adding the capability to the Landsat platform or by acquiring unrestricted targeted samples from government or commercial satellites. Without this medium- and high-resolution imagery, we will lose our capability to check the dominant source of agriculture, forestry, and other land-use (AFOLU) CO2 emissions. Recommendation. An interagency group, with broad participation from the research community, should undertake a comprehensive review of existing information and design a research program to improve and, where appropriate, implement methods for estimating agriculture, forestry, and other land-use emissions of CO2, N2O, and CH4. Methods for producing greenhouse gas inventories evolve as more is learned about how to measure and translate activities into emissions. Improvements to U.S. inventory methods could eventually become part of UNFCCC reporting through the established process managed by the IPCC. The most important component to improve is agriculture, forestry, and other land-use emissions of CO2, N2O, and CH4, which have the greatest uncertainties in the national inventories, primarily because of high uncertainty in emission factors. Continued research on the biogeochemical cycles of these gases is needed, especially on the CO2 emissions caused by deforestation and forest degradation, CH4 emissions from rice paddies and cattle, and N2O emissions from fertilizer application. Research is also needed on the natural cycles of CO2, N2O, and CH4 because natural emissions interfere with the detection of anthropogenic signals. This research has to be supported by ecosystem flux observations and ecosystem inventories. For example, eddy covariance towers measure the exchange of carbon between vegetation and the atmosphere at more than 100 sites in the United States. The towers provide valuable information on trends in ecosystem responses to management and climate, and a subset could be maintained to support verification research at relatively low cost (~$100,000 per station per year). As with fossil fuels, gridded inventories of emissions from agriculture, forestry, and other land use would facilitate cross-checks with other kinds of measurements recommended above. Currently, the only intensive U.S. ecosystem inventory focuses on forests (the U.S. Department of Agriculture’s [USDA’s] Forest Service Inventory and Analysis program). Making annual measurements of all the major carbon pools and their trends in other ecosystems—including croplands, pastures, and nonforested natural ecosystems—would greatly reduce their emissions uncertainties, which are commonly greater than 100 percent. The cost of a comprehensive ecosystem inventory would likely be substantially less than the cost of USDA’s forest inventory ($65 million per year), which includes more field sites (more than 100,000 plots) than are necessary for greenhouse gas monitoring. IMPLICATIONS FOR AN INTERNATIONAL CLIMATE AGREEMENT International agreements to limit future greenhouse gas emissions will require that countries be able to monitor and verify emissions as well as removals by sinks. Within a few years of their implementation, the above recommendations would establish rigorous annual national inventories of greenhouse gas emissions
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Verifying Greenhouse Gas Emissions: Methods to Support International Climate Agreements 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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