Atmospheric levels of CO₂ have risen from preindustrial levels of 280 parts per million (ppm) to present levels of 375 ppm. Evidence suggests this observed rise in atmospheric CO₂ levels is due primarily to expanding use of fossil fuels for energy. Predictions of global energy use in the next century suggest a continued increase in carbon emissions and rising concentrations of CO₂ in the atmosphere unless major changes are made in the way we produce and use energy—in particular, how we manage carbon. One way to manage carbon is to use energy more efficiently to reduce our need for a major energy and carbon source—fossil fuel combustion. Another way is to increase our use of low-carbon and carbon-free fuels and technologies (nuclear power and renewable sources such as solar energy, wind power, and biomass fuels). Both approaches are supported by the U.S. Department of Energy (DOE). The third and newest way to manage carbon is through carbon sequestration.

Carbon sequestration refers to the provision of long-term storage of carbon in the terrestrial biosphere, underground, or the oceans so that the buildup of carbon dioxide (the principal greenhouse gas) concentration in the atmosphere will reduce or slow. In some cases, this is accomplished by maintaining or enhancing natural processes; in other cases, novel techniques are developed to dispose of carbon. DOE's Office of Science is focusing its carbon sequestration efforts on:

• Sequestering Carbon in Underground Geologic Repositories: Geosciences research related to understanding the geophysics and geochemistry of potential reservoirs appropriate for subsurface sequestration of carbon dioxide.
• Enhancing the Natural Terrestrial Cycle: Identifying ways to enhance carbon sequestration of the terrestrial biosphere through CO₂ removal from the atmosphere by vegetation and storage in biomass and soils.
  Current Projects
• Carbon Sequestration in the Oceans: Enhancing the net oceanic uptake from the atmosphere by fertilization of phytoplankton with nutrients, and injecting CO₂ to ocean depths greater than 1000 meters.
• Sequencing Genomes of Micro-organism for Carbon Management: Sequencing the genomes of microbes that produce fuels such as methane and hydrogen or aid in carbon sequestration, to allow an evaluation of their potential use to produce, for example, methane or hydrogen from either fossil fuels or other carbonaceous sources, including biomass or even some waste products.

Understanding how carbon dioxide "sinks" perform so we can enhance the ongoing natural processes, and developing innovative new processes, may add powerful new measures to carbon management options.