Reactive nitrogen in the environment and its effect on climate change

Humans have doubled levels of reactive nitrogen in circulation, largely as a result of fertilizer application and fossil fuel burning. This massive alteration of the nitrogen cycle affects climate, food security, energy security, human health and ecosystem services. Our estimates show that nitrogen currently leads to a net-cooling effect on climate with very high uncertainty. The many complex warming and cooling interactions between nitrogen and climate need to be better assessed, taking also into account the other effects of nitrogen on human health, environment and ecosystem services. Through improved nitrogen management substantial reductions in atmospheric greenhouse gas concentrations could be generated, also allowing for other co-benefits, including improving human health and improved provision of ecosystem services, for example clean air and water, and biodiversity.

► Humans have doubled levels of reactive nitrogen in circulation, largely as a result of fertilizer application and fossil fuel burning. ► Initial quantifications of the effect of Nr on climate show that there is a small net cooling effect of −0.24 W m−2, with high uncertainty. ► The many complex warming and cooling interactions between nitrogen and climate need to be better assessed. ► Policies should be focused to both reduce effects on climate and environmental and human health impacts. ► This requires an integral and multi-disciplinary approach including: multi-source/actor, multi-pollutant, multi-problem, multi-benefits, multi-receptor, multi-effect, multi-scales, etc.