First North America carbon cycle report: continent responsible for 27 percent of global emissions, carbon sinks can't cope

For the first time, the U.S. Climate Change Science Program (CCSP) has published a report that quantifies North America’s net contribution of carbon to the atmosphere and catalogues sources and sinks of carbon on the continent. It finds a troubling imbalance: the continent’s carbon budget is increasingly overwhelmed by human-caused emissions. North American sources release nearly 2 billion tons of carbon into the atmosphere each year, mostly as carbon dioxide (graph 1, click to enlarge). Carbon 'sinks' such as growing forests remove less than a third of this amount, and may turn into new sources as climate changes. The findings have implications for the future of bioenergy on the continent.

This report serves an important function beyond being a critical part of the CCSP’s synthesis and assessment structure. It is also the first interagency State of the Carbon Cycle Report, which is a broadly conceived activity designed to provide accurate, unbiased, and policy-relevant scientific information concerning the carbon cycle to a broad range of stakeholders. It provides a baseline characterization of the North American carbon budget upon which future research and reports can build and refine. - Tony King, report team lead and staff scientist at the Energy Department’s Oak Ridge National Laboratory

The report titled The North American Carbon Budget and Implications for the Global Carbon Cycle analyzes the amounts of carbon emitted in the U.S., Canada and Mexico by industry sector, the amount absorbed naturally and how these amounts relate to the global carbon budget influenced by other regions of the globe, with particular attention given to characterizing the certainty and uncertainty with which these budget elements are known.

The report finds North America’s fossil fuel emissions represent approximately 27 percent of global emissions. The conversion of fossil fuels to energy, such as electricity generation, is the single largest carbon contributor, with transportation second but growing faster. The report details how the growth of vegetation blanketing North America absorbs carbon from the atmosphere.

Large imbalance between sources and sinks
The analysis points out a greater than three-to-one imbalance between the fossil fuel sources and the ability of vegetation to absorb carbon. This results in the large net release to the atmosphere (over one gigaton of carbon per year in 2003 - table 1, click to enlarge), but there is still some uncertainty in quantifying the North American sink compared to the carbon emission sources.

The carbon absorption by vegetation, primarily in the form of forest growth, is expected to decline as maturing forests grow more slowly and take up less carbon dioxide from the atmosphere.

Report authors find it unclear how rapidly this carbon storage 'sink' will decline and whether it might potentially become a source since changes in climate and atmospheric carbon dioxide could affect forest growth differently in different regions. Further warming, for example, could exacerbate drought, increasing carbon release through vegetation dieback and increased fire and insect disturbances:
energy :: sustainability :: biomass :: bioenergy :: biofuels :: climate change :: fossil fuels :: transportation :: greenhouse gas emissions :: carbon cycle :: carbon sinks :: forests :: North America ::

A variety of local, regional and national policy approaches could affect the overall North American carbon contribution. These include changing the rates of emissions through energy efficiency improvement, fuel switching to low carbon fuels (biomass), enhancing sinks in vegetation and soil, and implementing carbon capture and geological storage (CCS).

United States
Total United States emissions have grown at close to the North American average rate of about 1 percent per year over the past 30 years, but United States per capita emissions have been roughly constant.

Carbon intensity
The carbon intensity of the United States economy, which is the amount of carbon emitted per dollar of inflation adjusted GDP, has decreased at a rate of about 2 percent per year. The decline in the carbon intensity of the United States’ economy was caused both by increased energy efficiency, particularly in the manufacturing sector, and structural changes in the economy with growing contributions from sectors such as services with lower energy consumption and carbon intensity. The service sector is likely to continue to grow. Accordingly, carbon emissions will likely continue to grow more slowly than GDP.

Sectoral breakdown
The extraction of fossil-fuels and other primary energy sources and their conversion to energy products and services, including electricity generation, is the single largest contributor to the North American fossil-fuel source, accounting for approximately 42 percent of North American fossil emissions in 2003.

Electricity generation is responsible for the largest share of those emissions: approximately 94 percent in the United Sates in 2004, 65 percent in Canada in 2003, and 67 percent in Mexico in 1998. These are the latest years for which data are available.

More than half of the electricity produced in North America is consumed in buildings, making that single use one of the largest factors in North American emissions. In the United States, 67 percent is used in buildings.

In 2003, the carbon dioxide emissions resulting from energy consumed in United States buildings alone were greater than total carbon dioxide emissions of any country in the world except China. Energy use in buildings in the United States and Canada, including the use of natural gas, wood, and other fuels as well as electricity, has increased by 30 percent since 1990, corresponding to an annual growth rate of 2.1 percent.

In the United States, the major drivers of energy consumption in the buildings sector are growth in commercial floor space and increase in the size of the average home. Carbon emissions from buildings are expected to grow with population and income.

The report also characterizes in detail the uncertainty associated with these findings. Variability in physical processes, measurement error, and sampling error all contribute to uncertainty in quantifying elements of the North American carbon budget.

About the report and the CCSP
Authors were drawn from the broad scientific community and included scientists and researchers from academia, not-for-profit organizations, and governmental agencies. In addition, the process of developing this report involved stakeholders from various sectors who have an interest in managing carbon in the future.

Through this process, we are striving to ensure that the most relevant information about the carbon cycle is presented in a useful format for decision makers. - Lisa Dilling, assistant professor at University of Colorado, Boulder, and co-lead of the author team

All CCSP synthesis and assessment products are written as reports to U.S. Congress. Members of Congress have been briefed on the findings in Synthesis and Assessment Product 2.2. Also, all finalized synthesis and assessment products are signed by the secretaries of commerce and energy, as well as the president’s science advisor. National Air and Space Administration, NOAA, Department of Energy, National Science Foundation, U.S. Department of Agriculture, and U.S. Geological Survey provided funding for the report and/or support for federal agency authors in the development of SAP 2.2.

NOAA served as the lead agency for 2.2 for CCSP and administered the review, publication, and release of the report.

References:
U.S. Climate Change Science Program: North American carbon budget and implications for the global carbon cycle [Prototype State of the Carbon Cycle Report (SOCCR) focused on North America], Final Report, Synthesis and Assessment Product 2.2 [scroll down for chapters in *.pdf format] - November 2007.

Carnegie Institution for Science: First-ever State of the Carbon Cycle Report Finds Troubling Imbalance - November 14

National Oceanic and Atmospheric Administration: Government Science Panel Publishes Report on North America’s Carbon Budget - November 13, 2007