We have learned much about the workings of natural sinks like the oceans and terrestrial plants, but are just beginning to understand how their behavior might change as atmospheric CO2 concentrations rise. Organic carbon buried in sediments as coal, natural gas, and oil over literally hundreds of millions of years is being consumed as a result of human activities and returned to the atmosphere as carbon dioxide (CO2) on a time scale of a few centuries... Because of anthropogenic emissions, atmospheric CO2 has climbed to levels that are presently more than 30% higher than before the industrial revolution,1,2 as seen...