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Atmospheric Sciences & Global Change
Research Highlights

August 2007

PNNL Scientists, Computer Model Make Key Contributions to Major Climate Report

MiniCAM one of three models used to analyze greenhouse gas emissions

Scenarios of Greenhouse Gas Emissions and Atmospheric Concentrations
Global-Change Scenarios
The recent two-part report is the second in a series of 21 Synthesis and Assessment products commissioned by the U.S. Climate Change Science Program.

In July, the U.S. Climate Change Science Program released a new report that provides a long-term, global reference for greenhouse gas stabilization scenarios and an evaluation of the process by which scenarios are developed and used. The report shows that stabilizing the concentration of carbon dioxide—the most important greenhouse gas released by human activities—requires global emissions to peak in the 21st century and then decline indefinitely thereafter. Pacific Northwest National Laboratory's integrated assessment model, MiniCAM was one of three models used to analyze emissions scenarios.

"This report is the first major assessment of the energy, economic, and land-use implications of stabilizing global change," said PNNL scientist Jae Edmonds, a co-author for the report. He added that the report is also the first major assessment since the Special Report on Emissions Scenarios, published in 2000 by the Intergovernmental Panel on Climate Change, to "extensively review the forces shaping the next century's global energy and economic system."

Along with Edmonds, Leon Clarke and Hugh Pitcher, all PNNL scientists at the Joint Global Change Research Institute, co-authored sections of the report. In addition, Clarke was the leader for the overall study. Titled "Scenarios of Greenhouse Gas Emissions and Atmospheric Concentrations, and Review of Integrated Scenario Development and Application," the report is presented in two parts.

Part A, "Scenarios of Greenhouse Gas Emissions and Atmospheric Concentrations," uses model-generated scenarios to evaluate four alternative stabilization levels of greenhouse gases in the atmosphere and the implications to energy and the economy for achieving each level. Part B, "Global-Change Scenarios: Their Development and Use," examines how scenarios have been developed and used in global climate change applications, evaluates the effectiveness of current scenarios, and recommends ways to make future scenarios more useful.

Edmonds and colleagues at the Joint Global Change Research Institute originally developed and continue to refine the MiniCAM. It was chosen as one of three "integrated assessment" models used to develop the scenarios evaluated in Part A of the report. Integrated assessment models are analysis tools that combine information pertaining to economic, energy and climate variables across various scientific disciplines, time, and spatial scales. According to Edmonds, each of the three modeling teams brought important relative strengths to the assessment.

"One of the MiniCAM's relative strengths was its representation of energy technology," said Edmonds. "It contains detailed representations of energy technology in energy supply, energy transformation—like electricity or hydrogen—energy use, such as in buildings, industry, and transportation, and agriculture and land use."

Part A of the report uses a reference case with no new measures instituted to limit emissions, plus four scenarios that assume widespread development and deployment of alternatives to fossil fuels over the next century. All three modeling teams ran the same stabilization experiments; however, each team made its own choices about demographics, basic economic drivers to the economy, energy technology, and atmospheric processes.

With a focus on technology development, the MiniCAM shed light on the importance of major technology systems that included carbon dioxide capture and storage, biotechnology, nuclear energy, wind energy, solar energy, power generation, building energy use, industrial energy use, and transportation technology.

Edmonds explained that energy technology is a major determinant of the cost of stabilizing climate change, and MiniCAM provided unique insights due to its emphasis in this area. One of these insights was the importance of valuing carbon in natural systems at the same level as fossil fuel carbon (see sidebar).

Another insight, gained from examining the variation in greenhouse gas prices across the three modeling teams, was the importance of technology development and availability in the post-2050 timeframe. The state of these capabilities will be heavily dependent on related investments in the coming decades.

"Insights like these are very difficult to obtain without an integrated approach that links knowledge about the energy system, agriculture and land use, and atmospheric processes," said Clarke.

Part B of the report, which examines the development and effectiveness of the scenarios, concludes that useful scenarios require a blend of scientific knowledge with judgment and speculation. To support diverse climate-related decisions, the authors advocate greater transparency about the assumptions and reasoning underlying scenarios, including more explicit statements of developers' probability judgments. They also recommend an expanded capacity to commission, disseminate, document, and evaluate scenarios and related decision-support tools.

Acknowledgments: Authors involved in Part A of the report include: Leon Clarke, James Edmonds, and Hugh Pitcher, all of the Pacific Northwest National Laboratory and Joint Global Change Research Institute, a partnership with the University of Maryland; Henry Jacoby and John Reilly, Massachusetts Institute of Technology; and Richard Richels, Electric Power Research Institute.

For Part B, authors include Edward Parson, University of Michigan; Virginia Burkett, U.S. Geological Survey; Karen Fisher-Vanden, Dartmouth College; David Keith, University of Calgary; Linda Mearns, National Center for Atmospheric Research; Hugh Pitcher, Pacific Northwest National Laboratory; Cynthia Rosenzweig, NASA Goddard Institute for Space Studies; and Mort Webster, Massachusetts Institute of Technology.

This report was coordinated by the U.S. Department of Energy, one of 13 federal agencies that make up the Climate Change Science Program. The Climate Change Science Program was established in 2002 to integrate federal research on global environmental change at 13 federal agencies, and to provide the nation with science-based knowledge to manage the risks and opportunities of change in the climate and related environmental systems. For more information on this report and the program, visit the Global Change Research Program.

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Bioenergy - a careful balance between nature and energy demand

As the name suggests, bioenergy is derived from crops grown for their energy content.  They are a hydrocarbon, like oil, gas, or coal, but unlike their fossil fuel cousins, they derived their carbon very recently from the atmosphere. Thus, when it is burned for fuel, the net carbon dioxide concentration in the atmosphere remains largely unchanged.

As the attractiveness of bioenergy relative to fossil fuels grows, so does the demand for land. That increasing demand for land creates pressure to take lands out of unmanaged ecosystems—like tropical forests—to use for managed systems such as crops, livestock, and forests, as well as biofuels.

Enormous amounts of carbon are tied up in forests and soils. Deforesting such lands to bring them under cultivation for bioenergy releases the previously stored carbon into the atmosphere. One hundred years of carbon accumulation in soils and forests could be put into the atmosphere overnight.

If the carbon tied up in forests and soils are not valued at the same rate as carbon in the fossil fuels, too much land will be deforested, and not enough land will be used to store carbon in soils and forests. Taken to the extreme, this could lead to massive deforestation and both a climate and environmental disaster.