Ralph Keeling, the director of an acclaimed Scripps program that keeps track of the amounts of carbon dioxide and oxygen in the atmosphere, has renewed his plea for public support of the research, which has suffered from flagging federal grants. "The Scripps CO2 and O2 measurements now face severe funding challenges," Keeling wrote in a letter posted on Dec. 24. "The situation is most urgent for the O2 measurements. These measurements have been supported for decades through proposals submitted every few years to the federal agencies. The value of these measurements is not questioned, but federal funding for these programs has never been so tenuous." The work at Scripps Institution of Oceanography at UC San Diego has led to many findings beyond just showing how much carbon dioxide and oxygen are in the air at any given moment, although that measurement has generated the most headlines—such as when carbon dioxide levels surpassed 400 parts per million, more than at any time in human history.