The climatic benefits of nitrogen additions to terrestrial ecosystems are offset by increased nitrous oxide emissions, reports a study published online this week in Nature Geoscience. Additions of reactive nitrogen to terrestrial ecosystems have more than doubled since 1860 as a result of human activities.

Sonke Zaehle and colleagues used a terrestrial biosphere model to examine the impact of human nitrogen additions to terrestrial ecosystems on climate. They show that nitrogen inputs accounted for about one fifth of the carbon sequestered by terrestrial ecosystems between 1996 and 2005, and for most of the increase in global nitrous oxide emissions in recent decades. They conclude that nitrogen-induced reductions in radiative forcing due to carbon sequestration are offset by nitrous oxide emissions.