Trust in international agreements to limit future greenhouse gas emissions will depend on the ability of each nation to make accurate estimates of its own emissions, monitor their changes over time, and verify one another's estimates with independent information. Countries have the capability to estimate their carbon dioxide emissions from fossil-fuel use with sufficient accuracy to support monitoring of an international treaty, but accurate methods are not universally applied and the estimates cannot now be checked against independent data. Deployment of existing methods and technologies could, within five years, yield a capability to both estimate and verify carbon dioxide emissions from fossil-fuel use and deforestation—which comprise approximately three-quarters of greenhouse emissions likely covered by a treaty.
The Importance of Emissions Verification
Why is verification of greenhouse gases so important?
Dr. Stephen Pacala, who led the committee that developed this report, explains why it is critical to have reliable data on greenhouse gas emissions.
Agreements to limit future emissions of greenhouse gases are the focus of international negotiations, and with such accords will come the need to accurately estimate emissions and 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 identify ways to improve these capabilities.
The committee focused on human-made emissions of six greenhouse gases that have long lifetimes in the atmosphere and therefore will affect global climate for decades or even millennia to come: 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. Particular focus was given to CO2 because this greenhouse gas is the largest single contributor to global climate changes. Only data in the public domain were considered because public access and transparency are necessary to build trust in a climate treaty.
The committee examined three categories of methods for estimating greenhouse gas emissions: national inventories, atmospheric and oceanic measurements and models, and land-use measurements and models (Box 1). The first method is used by countries to estimate and report their emissions to the international community under the United Nations Framework Convention on Climate Change (UNFCCC); the second and third are research methods that could help verify self-reported estimates. The committee found that deploying existing methods and technologies could, within five years, yield a capability to estimate and verify carbon dioxide emissions from fossil-use and deforestation more accurately. As these types of emissions comprise about three-quarters of the greenhouse emissions likely to be covered by a treaty, these improved capabilities could provide useful support to international negotiations.
Figure 1. Select one of the options below to isolate developing or developed nations on the graph, or to restore the full graph:
Click here for developing countries
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To view both developing and developed countries together, click here.
Sources of greenhouse gas emissions in 2000. In general, energy production and use are the largest sources of emissions for developed countries; whereas agriculture and deforestation are generate the most greenhouse gases in developing countries. SOURCE: Data from the World Resources Institute.
Current methods produce emissions estimates with unacceptably high uncertainties; in some cases the uncertainties are larger than the expected emissions reductions over a treaty's lifetime (Table 1, downloadable here as a PDF file). However, it may not be necessary to accurately measure all greenhouse gases to support treaty monitoring and verification. Approximately 90% of global emissions covered by the UNFCCC (Box 1) are from energy and agriculture, forestry, and other land use, making these activities an obvious focus for monitoring. The majority of emissions are in the form of CO2 from fossil-fuel use, which can be estimated accurately (see box, "Sources of Greenhouse Gases," below).
Box 1: Current Methods for Estimating Greenhouse Gas Emissions
UNFCCC national inventories
Countries calculate emissions by multiplying levels of greenhouse gas-emitting activities—such as energy production and use; industrial processes and product use; agriculture, forestry, and other land use; and waste—by the corresponding rate of emission per unit of activity.Atmospheric and oceanic measurements (tracer-transport inversion)
Emissions of total human-made and natural sources and sinks of greenhouse gases are estimated using atmospheric and oceanic measurements of greenhouse gases and models of air and water flow.Land-use measurements and models
Satellite information on land-surface characteristics and change is converted into CO2, CH4 and N2O emissions estimates using biogeochemical models constrained by measurements of greenhouse gas exchange between the land and the atmosphere.
Recommendations
Strategic investments focused on the most important sources of greenhouse gases, the most abundant and longest-lived gases, and the highest emitting countries, could yield an improved ability to monitor and verify an international climate agreement within five years. The required investments are in three categories: strengthening national greenhouse gas inventories, improving independent estimates of fossil-fuel CO2 emissions, and improving independent estimates of fluxes from land use.
Strengthening National Greenhouse Gas Inventories
The UNFCCC framework will likely form the basis for a future climate agreement, because it has broad international support, and offers established mechanisms for preparing national inventories of emissions and incorporating new information and methods. However, the framework also has several shortcomings. For example, developing countries do not measure or report their emissions regularly, even though rapidly industrializing countries are among the world's highest emitters of greenhouse gases. Under the UNFCCC, developed countries produce detailed annual estimates of sources and sinks of six greenhouse gases using complex methods and country-specific data on emissions generating activities, and the resulting national inventories are subject to international review of methods and data sources. If applied, these rigorous methods allow countries to estimate CO2 emissions from fossil-fuel use with uncertainties of less than 10 percent. In contrast, developing countries are required to make only periodic estimates of CO2, CH4, and N2O, and the methods used to calculate emissions are simple, less accurate, rely only on global data, and are not reviewed. Financial and technical assistance will be required for developing countries to build the capacity to collect, analyze, and report emissions regularly.
extending regular, rigorous reporting and review to developing countries
extending the most stringent inventory methods to the most important greenhouse gas sources in each country
Costs could be kept down by using the most stringent, accurate methods to calculate emissions from only the largest sources of greenhouse gases in each country. Agriculture and deforestation activities produce the majority of emissions in most from developing countries (see Figure 1, above). Implementation of land cover mapping recommended below would reduce inventory costs for these countries.
Sources of Greenhouse Gases
Global human-caused greenhouse gas emissions for 2004, categorized by the activity that generated them, covered by the United Nations Framework Convention on Climate
Change (UNFCCC). The gases are weighted by their potential to contribute to global warming over 100 years.
SOURCE: Figure 1.1b from IPCC (2007b), Cambridge University Press.
Emissions of CH4 and N2O are primarily produced by agricultural activities. Uncertainties for these gases are high and are likely to remain so for several years. Emissions of CO2 from fossil-fuel use and deforestation account for the majority of greenhouse gases covered by the UNFCCC. If the recommendations in this report are implemented, both emission sources could be estimated and verified accurately enough to support an international treaty within five years.
Improving Independent Estimation of Fluxes from Land-Use Sources and Sinks
Measurements of emissions and absorption of CO2, CH4, and N2O from land-use activities such as agriculture and forestry currently have the highest uncertainties in national inventories, commonly greater than 100 percent. Satellite imagery provides an independent check on the activities that create the largest CO2 emissions from land use. Publicly-available Landsat imagery, supplemented with high-resolution imagery which can distinguish areas undergoing logging and forest degradation even down to detecting single trees, could be used to create a gridded map that would allow countries to validate land-use emissions anywhere in the world. Such a map would also help developing countries improve estimates of their dominant emissions source.
Establish a standing group to produce a global map of land use and land cover change at least every two years. This will require a commitment to maintaining the continuous availability, in the public domain, of Landsat and high-resolution satellite imagery
Natural emissions of CO2, CH4, and N2O can interfere with the detection of human-made emissions. Research on the natural cycles of these gases and on CO2 emissions caused
by deforestation and forest degradation, CH4 emissions from rice paddies and cattle, and N2O emissions from fertilizer application would yield long-term improvements in
the accuracy of emissions caused by land use.An interagency group, with broad participation from the research community, should design a research program to improve methods for estimating agriculture, forestry, and other land-use emissions of CO2, CH4, and N2O.
Improving Independent Estimation of Fossil-fuel CO2 Emissions
Measurements of atmospheric abundances of greenhouse gases could be used to independently verify self-reported emissions estimates; however, these measurements currently have uncertainties of 100% or more at national scales. This is because the transport of emissions through the atmosphere is not well understood, large and incompletely understood background fluctuations of natural emissions obscure the fraction of emissions caused by human activities, and the observing network is sparse, often missing the urban areas and large industrial sources which generate most emissions. Implementation of the recommendations below would help improve understanding of the transport of emissions through the atmosphere, overcome the background noise generated by the natural variability of the atmosphere, sample the large urban and industrial sources, and provide the capability to verify self-reported estimates of fossil-fuel CO2 emissions.
The National Aeronautics and Space Administration should build and launch a replacement for the Orbiting Carbon Observatory
The abundance of CO2 in the atmosphere is highest over emission sources and disperses within a few tens of kilometers. CO2 created by large local sources such as cities
and power plants could have been detected by NASA's Orbiting Carbon Observatory, which failed on launch in February 2009. This satellite offers higher precision
and a smaller sampling area that any CO2-sensing satellite already in use, and also offers the ability to sense CO2 near Earth's surface—qualities needed to monitor
large local sources and to attribute their CO2 emissions to individual countries. The two-year mission would demonstrate that it is possible to monitor large local sources
of CO2 from space and also provide baseline atmospheric data against which to measure future trends.Extend the international atmospheric sampling network to research greenhouse gas emissions 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
Large local sources could also be monitored using atmospheric sampling stations deployed on the land surface. Most stations in the international atmospheric
sampling network were deliberately located far from cities and power plants in order to better observe the natural cycles of greenhouse gases. However, adding stations
in or around large sources of emissions would provide data for monitoring as well as for "ground-truthing" CO2 measurements from the Orbiting Carbon Observatory—that
is, provide ground data to interpret the satellite measurements. In addition, large areas of the planet, such as Africa and South America, have few measurement stations.
Adding atmospheric sampling stations to the undersampled countries with the highest emissions would greatly improve capabilities to independently verify self-reported
emissions estimates.Extend the capability of the CO2 sampling network to measure atmospheric radiocarbon
Measurements of radiocarbon (C14) in the CO2 samples already being collected would allow fossil-fuel CO2 emissions to be separated from non-fossil fuel
emissions—modern organic material contains radiocarbon from cosmic rays and bomb tests, but the radiocarbon in fossil fuels has long since decayed away.
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. Within a few years of their
implementation, the above steps would establish rigorous annual national inventories of greenhouse gas emissions, enabling every country to estimate the largest sources
of emissions—CO2 from fossil-fuel use and deforestation—to 10% uncertainty. They would also provide independent and transparent checks on emissions from these sources with the same accuracy. Finally, targeted research would ultimately lead to improved monitoring and verification of all greenhouse gases.