Rivers and streams in the United States are releasing significantly more carbon dioxide into the atmosphere than previously thought -- enough for a car to drive back and forth to the moon 3.4 million times each year, a new study finds.Scientists find that carbon, after decomposing from plants, is discharged into streams and rivers and then outgassed as carbon dioxide (CO2) into the atmosphere at a rate equal to a car burning 40 billion gallons of gasoline, according to the U.S.-funded study by David Butman and Peter Raymond of the Yale School of Forestry and Environmental Studies. The study appears in the current issue of the journal Nature Geoscience.FOLLOW:  Green House on Twitter"These rivers breathe a lot of carbon. They are a source of carbon dioxide, just like we breathe out carbon dioxide and like smokestacks emit carbon dioxide," Butman said in announcing the findings. "This has never been systematically estimated from a region as large as the United States."The authors, who analyzed data from samples of more than 4,000 rivers and streams throughout the United States, said climate warming will bring more rain and snow. They said this precipitation will increase carbon flowing into waterways and being released into ...