A recent paper published in the Journal Nature by Dean et al. provides an interesting and compelling argument that a significant source of atmospheric CO2 has been underestimated by carbon budget models. The study, Old carbon routed from land to the atmosphere by global river systems looks at the origin of the CO2 released by river water into the atmosphere and concludes that the amount of ancient (millennia old) CO2 is higher than has been used in the current carbon cycle models.