WASHINGTON - What would it take for the world to achieve a stable concentration of greenhouse gases in the atmosphere? A new report from the U.S. Climate Change Science Program examines the scenarios needed to stabilize carbon dioxide concentrations at 450 parts per million (ppm), 550 ppm, 650 ppm, and 750 ppm. The report also includes a reference scenario in which no new climate goals are set after the Kyoto Protocol expires and after the United States meets its greenhouse gas intensity goals, both of which are scheduled for 2012. Three different modeling groups independently examined each of the five scenarios, and the report compiles all of their results.
All the groups agreed on a basic finding of the report - to stabilize greenhouse gases in the earth's atmosphere will require a transformation of the global energy system, cutting fossil fuel use and reducing the growth in demand for energy. All of the scenarios found that greenhouse gas emissions cuts were achieved at the lowest cost by the electric power industry, using such technologies as renewable energy, nuclear power, and carbon dioxide capture and storage. Other sectors of the economy, such as buildings, industry, and transport, could mainly achieve emissions reductions through the use of energy efficiency; biomass energy and biofuels; electricity generated from low-carbon sources; and, when possible, carbon dioxide capture and storage.
Under the most stringent scenarios, greenhouse gas emissions begin to decline immediately or within a few decades, while the less stringent scenarios result in peak emissions late in this century or beyond, causing earth's atmosphere to increase its heat-trapping ability by as much as a factor of 2.5. In contrast, the reference scenario projects the heat-trapping ability of earth's atmosphere increasing by a factor of three to four by 2010 and trending upward, as economic growth outweighs improvements in energy efficiency. The report was coordinated by the U.S. Department of Energy (DOE).