By JOHN M. BRODER
Even if the United States takes no explicit action to regulate greenhouse gases, emissions of carbon dioxide and other climate-altering substances will grow slowly over the next two decades, not returning to 2005 levels until 2027, according to a new projection from the Energy Information Administration, the research branch of the Energy Department.
Carbon dioxide emissions fell by 3 percent in 2008 and 7 percent in 2009, largely because of the recession. But even as economic activity picks up, emissions will grow at a modest pace because of growing use of renewable technologies and fuels, improved energy efficiency, slower growth in demand for electricity and the growing substitution of natural gas for coal in power production, the agency reports in its annual energy outlook.
The E.I.A. projects that energy-related emissions will not reach six billion metric tons, the 2005 level, until 2027, and will then rise by an additional 5 percent by 2035, reaching 6.3 billion metric tons. United States population and energy use will rise in that period, meaning that per-capita carbon dioxide emissions will fall.
Those figures assume that Congress and future administrations take no aggressive action to reduce greenhouse gas emissions and that coal will remain the dominant source of electricity generation. The outcome could be different if the country moves more quickly to renewable fuel sources or if economic growth is faster or slower than projected.