A release from NAS explains that agreements to limit emissions of greenhouse gases are currently the focus of international negotiations, and with such accords will come the need to accurately estimate these emissions and monitor their changes over time. Stephen Pacala, chair of the committee that wrote the report from Princeton University said, "For any international agreement to limit greenhouse gas emissions, it would be essential for each country to monitor its own emissions and to provide a transparent capability for any nation to check the values reported by another. This would give nations confidence that their neighbors are living up to their commitments."
Under the United Nations Framework Convention on Climate Change (UNFCCC), countries are currently required to estimate their greenhouse gas emissions by identifying human activities that cause emissions, and then multiplying each activity by its rate of emissions. The level of uncertainty in these self-reported estimates depends on each country's institutional and technical capabilities. The committee focused on carbon dioxide because it is the largest single contributor to global climate change and is thus the focus of many mitigation efforts. Estimates of emissions of greenhouse gases other than carbon dioxide are likely to remain relatively uncertain, the report says.
The report indicates that because UNFCCC procedures have broad international support and can estimate carbon dioxide emissions from fossil fuels with reasonable accuracy, they will likely continue to be the primary way to monitor emissions under any new climate treaty. "But the reporting system has shortcomings. Developing countries do not provide regular, detailed emissions reports, for example, and independent data to check self-reported emissions is limited. In addition, there are large uncertainties in estimates of the carbon dioxide and other greenhouse gases released into or removed from the atmosphere because of changes in land use, such as deforestation or reforestation."
The report recommends ways to overcome these weaknesses and indentifies methods that could improve both self-reported estimates and other nations' ability to verify them. The Committee said, "Regular, rigorous reporting and review should be extended to all countries. And the most stringent and accurate methods for calculating greenhouse gas emissions should be used for the largest emissions sources in each country, which in some cases may be deforestation and agriculture rather than fossil-fuel use." They said that financial and technical assistance will be required for developing countries to build an ongoing capacity to collect, analyze, and report emissions information regularly. The Committee indicates that significant improvements in the accuracy of the inventories from 10 of the highest-emitting developing countries, such as China and India, could be achieved for approximately $11 million over five years.
The report says that enabling independent verification of countries' self-reported estimates will require additional atmospheric measurements and improved models to predict the movement of greenhouse gases in the atmosphere. It recommends that new monitoring stations be established near cities and other large local emissions sources. In addition, NASA should build and launch a replacement for the Orbiting Carbon Observatory, which failed at launch in February 2009. Such an observatory could monitor carbon dioxide emissions from cities and power plants and attribute them to individual countries; no other satellite has its critical combination of abilities, including high precision, a small footprint, and an ability to sense carbon dioxide near Earth's surface.
Using improved methods, fossil-fuel carbon dioxide 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 carbon dioxide emissions next to fossil-fuel use, and for growth of new forests, which is an important "sink" for reducing carbon dioxide. The report recommends that to aid efforts to understand how greenhouse gases are affected by land use, a working group should be established to produce publicly available global maps of land use and land cover change at least every two years, using Landsat and high-resolution satellite imagery. In addition, an interagency group with broad participation from the research community should design a program to improve ways to estimate how agriculture, forestry, and other land uses affect emissions of carbon dioxide, nitrous oxide, and methane.
The report also recommends that the isotope carbon-14 should be measured in the carbon dioxide already collected at atmospheric sampling stations. Carbon-14 is present in living organisms but not in fossil fuels, so it provides a way to discern whether carbon dioxide is generated from fossil-fuel or non-fossil-fuel sources. These measurements could be made by the National Oceanic and Atmospheric Administration (NOAA), a national laboratory, or a university at a cost of approximately $5 million to $10 million per year.