title: Climate change impacts of US reactive nitrogen.
abstract: Fossil fuel combustion and fertilizer application in the United States have substantially altered the nitrogen cycle, with serious effects on climate change. The climate effects can be short-lived, by impacting the chemistry of the atmosphere, or long-lived, by altering ecosystem greenhouse gas fluxes. Here we develop a coherent framework for assessing the climate change impacts of US reactive nitrogen emissions, including oxides of nitrogen, ammonia, and nitrous oxide (N(2)O). We use the global temperature potential (GTP), calculated at 20 and 100 y, in units of CO(2) equivalents (CO(2)e), as a common metric. The largest cooling effects are due to combustion sources of oxides of nitrogen altering tropospheric ozone and methane concentrations and enhancing carbon sequestration in forests. The combined cooling effects are estimated at -290 to -510 Tg CO(2)e on a GTP(20) basis. However, these effects are largely short-lived. On a GTP(100) basis, combustion contributes just -16 to -95 Tg CO(2)e. Agriculture contributes to warming on both the 20-y and 100-y timescales, primarily through N(2)O emissions from soils. Under current conditions, these warming and cooling effects partially offset each other. However, recent trends show decreasing emissions from combustion sources. To prevent warming from US reactive nitrogen, reductions in agricultural N(2)O emissions are needed. Substantial progress toward this goal is possible using current technology. Without such actions, even greater CO(2) emission reductions will be required to avoid dangerous climate change.
authors.affiliation: Office of Research and Development, US Environmental Protection Agency, Durham, NC 27711, USA. pinder.rob@epa.gov
authors.forename: Robert W
authors.initials: RW
authors.lastname: Pinder
authors.forename: Eric A
authors.initials: EA
authors.lastname: Davidson
authors.forename: Christine L
authors.initials: CL
authors.lastname: Goodale
authors.forename: Tara L
authors.initials: TL
authors.lastname: Greaver
authors.forename: Jeffrey D
authors.initials: JD
authors.lastname: Herrick
authors.forename: Lingli
authors.initials: L
authors.lastname: Liu
mesh_terms: D000383:Agriculture; D000397:Air Pollution / Q000009:adverse effects* / Q000032:analysis; D002245:Carbon Dioxide / Q000737:chemistry*; D057231:Climate Change; D017753:Ecosystem; D005390:Fires; D008962:Models, Theoretical; D058458:Nitrogen Cycle; D009589:Nitrogen Oxides / Q000009:adverse effects* / Q000737:chemistry; D010126:Ozone / Q000737:chemistry; D013696:Temperature; D014481:United States
chemical_list: D009589:Nitrogen Oxides; D002245:Carbon Dioxide; D010126:Ozone