The earth is retaining more of the sun's energy than it is sending back into space, scientists say. That is the conclusion from a new simulation that takes into account such climate forcing variables as greenhouse gas and aerosol concentrations, land use and surface reflectivity, and that calculates global temperatures and other climate values for the atmosphere and the oceans. And a decade of measurements of the heat content of the oceans confirm the model's findings, its creators report in a paper published online Thursday by the journal Science.

James Hansen of NASA's Goddard Institute for Space Studies and his colleagues developed a model to simulate climate change between 1880 and 2003. The results indicate that our planet is absorbing a net amount of energy equal to about 0.85 watt per square meter. With no additional input, this imbalance could cause additional warming worldwide of 0.6 degree Celsius by the end of the century, the team reports, because the world's oceans take longer to respond to shifts in ratiation than the atmosphere does. In fact, another report published last month in Science determined that even if greenhouse gas emissions had stalled five years ago, global temperatures would still increase by about half a degree by the end of the century.

Hansen and his colleagues also analyzed data collected by floats deployed around the globe, ships traveling across the oceans and satellite altimetry measurements of sea level. "Warmer waters increase the likelihood of accelerated ice sheet disintegration and sea level rise during this century," Hansen says. The delay provides an opportunity to reduce the magnitude of climate change before it is fully realized, the authors argue, but appropriate action must be taken. "The most effective actions that we could take now are strong efforts to improve energy efficiency, employ renewable energies, and reduce air pollutants, especially fugitive methane, other ozone precursors, and black carbon (soot)," Hansen remarks. "[In] the long-run we will need either carbon-free power sources or we will need to capture and sequester CO2.