Carbon Cycling and Sequestration
Understand Biosystems’ Climate Impacts and Assess Sequestration Strategies
The Climate Change Challenge
The United States is committed to understanding the factors that influence climate change, reducing uncertainties in assessments of climate change, and developing strategies to mitigate change. Microbes in the earth’s oceans and soils play a major role in the cycling of carbon and other elements. GTL seeks to understand this role to be able to predict the impacts of climate change on microbes and their responses to the resulting ecosystem shifts. This knowledge also will provide the basis for developing and assessing strategies for ocean- and soil-based carbon sequestration.
Mission Science Goals and Challenges
Mission Science Goals: Understand the microbial mechanisms of carbon cycling in the earth’s ocean and terrestrial ecosystems, the roles they play in carbon sequestration, and how these processes respond to and impact climate change. Develop methods to relate genome-based microbial ecophysiology (functionality) to the assessment of global carbon-sequestration strategies and climate impacts.
Challenges: We are just beginning to understand the genetic and functional diversity of ocean and terrestrial ecosystems. They potentially contain millions of microbial species organized in extensive communities. We must understand both the global and molecular mechanistic behaviors of these large systems.
Atmospheric greenhouse gas (GHG) concentrations have been increasing for about 2 centuries, mostly as a result of human (anthropogenic) activities, and now are higher than they have been for over 400,000 years. As shown in the Simplified Representation of the Global Carbon Cycle, about 6 billion tons (gigatons) of carbon are released into the air by human activity each year, three-quarters from the burning of fossil fuels and the rest from deforestation and other changes in land use, with a small amount from cement production. Although the effects of increased levels of CO2 on global climate are uncertain, many agree that a doubling of atmospheric CO2 concentrations, predicted for the middle of this century by the Intergovernmental Panel on Climate Change (IPCC), could have a variety of serious environmental consequences.
Global climate change is a long-term energy and environmental challenge requiring major investments in targeted research and development. Gaining a greater knowledge of how carbon cycles through ecosystems is a critical element of the national strategy to understand climate and potential changes that might occur due to anthropogenic greenhouse gases and to develop solutions to reduce future increases in CO2 (the most important GHG) and other GHGs. Understanding how climate affects both natural and managed “pools” (e.g., forest, agriculture lands) of carbon stored in global ecosystems and how these carbon “sinks” influence atmospheric concentrations of CO2 will be important in reducing uncertainty in climate models and in understanding the long-term sequestration capacity of those pools (Carbon Sequestration 1999).
The Role of Microbes
Natural processes also contribute to the storage and cycling of carbon. The stability and sequestration of vast pools stored in oceanic and terrestrial environments depend, in part, on the microbial world.
According to the American Society of Microbiology (King et al. 2001), “Microbes, responsible for transforming many of earth’s most abundant compounds, cannot be ignored in the search for scientific solutions to adverse global changes. . . . Both the ubiquity of microbes and the delicacy of environmental balances contribute to [the planet’s] sensitivity to disturbances in the microbial world.”
Microbial energy transfer and material processing in the biosphere have been transforming the earth for over 3 billion years and influencing climate on a global scale (Staley et al. 1997). Extremely diverse ocean and terrestrial microbial communities serve fundamentally different roles in the carbon cycle as primary photosynthetic producers of biomass in the ocean biological “pump” and as carbon and nutrient managers and decomposers in terrestrial systems. Microbes cycle immense volumes of carbon in the process of recycling most of earth’s biomass: They can fix CO2 by light-driven (photoautotrophy) and geochemically driven (lithoautotrophy) reactions, generate methane, produce CO2 as they decompose organic matter, precipitate carbonate minerals, and catalyze the polymerization of plant polymers into recalcitrant pools of carbon in soil.
The DOE mission of global carbon management requires that we achieve a comprehensive understanding of terrestrial and marine microbial communities so we can learn the role that these communities play in carbon sequestration. We then must find ways to enhance their capabilities to develop microbe-based strategies for capturing and sequestering atmospheric CO2 and to assess the potential effectiveness and adverse ecological impacts of proposed carbon-sequestration technologies. Microbial systems also have great potential as sensitive indicators of environmental change.
Natural cycles of carbon in the environment involve exchanges many times greater than anthropogenic emissions. While anthropogenic emissions threaten to change the globe’s climate gradually, secondary effects on natural ecosystems and disturbance of their much larger atmospheric exchanges could result in even larger shifts. Knowing the effects of anthropogenic emissions on natural cycles is important as part of the complete picture of carbon management on a global scale.
Investigating and understanding these ecosystems require probing numerous complementary functionalities in thousands of species and millions of genes, involving hundreds of thousands of proteins. In brief, goals and challenges in this mission follow.
Carbon Cycling and Sequestration: Goals and Impacts
- Improved understanding of key feedbacks and sensitivities of biological and ecological systems and accelerated incorporation into climate models will reduce uncertainties in assessments of climate change.
- Knowledge of the carbon cycle will allow evaluation of carbon-sequestration strategies and alternative response options.
- Development of sensors and monitoring techniques and protocols will allow use of these sensitive ecosystems as sentinels for the effects of climate change.
Terrestrial Microbial Communities
Text adapted from Genomics:GTL Roadmap: Systems Biology for Energy and Environment, U.S. Department of Energy Office of Science, August 2005. DOE/SC-0090.
