Image credit: NOAA Great Lakes Environmental Research Laboratory
Perspectives essay, co-authored with the executive director of the Pacific Institute for Climate Solutions, Sybil Seitzinger. Published July, 2017.
Nitrogen compounds, mainly from agriculture and sewage, are causing widespread eutrophication of estuaries and coastal waters (1). Rapid growth of algal blooms can deprive ecosystems of oxygen when the algae decay, with sometimes extensive ecological and economic effects. Nitrogen oxides from fossil fuel combustion also contribute to eutrophication, and nitrous oxide, N2O, is an extremely powerful greenhouse gas (GHG). On page 405 of this issue, Sinha et al.confirm that climate change is worsening nitrogen pollution, notably coastal eutrophication (2). The results highlight the urgent need to control nitrogen pollution. Solutions may be found by drawing on decarbonization efforts in the energy sector.
Increased precipitation and greater frequency and intensity of extreme rainfall events will see increased leaching and run-off—or nitrogen loading—in many agricultural areas in the United States. Sinha et al. show that, in the Mississippi-Atchafalaya River Basin, a business-as-usual emission scenario leads to an 18% increase in nitrogen loading by the end of the 21st century, driven by projected increases in both total and extreme precipitation. To counter this, a 30% reduction in anthropogenic nitrogen inputs in the region would be required. Farmers here already are trying to achieve a 20% loading reduction target imposed by the U.S. Environmental Protection Agency (EPA), requiring a 32% reduction in nitrogen inputs to the land. To offset the climate-induced boost to nitrogen pollution in addition to meeting this target would thus require a 62% reduction in nitrogen inputs, a colossal challenge for any farmer.
As Sinha et al. show, regions with historically substantial rainfall, high nitrogen inputs, and projected robust increases in rainfall are most likely to experience increased coastal nitrogen loading (2). This includes great swaths of east, south, and southeast Asia, India, and China—regions where coastal eutrophication already occurs.
Solutions to coastal eutrophication and climate change are closely intertwined. To stay below a 2°C increase in global average temperature will require attaining net zero GHG emissions soon after mid-century (3). To achieve this goal, fossil fuel combustion must plummet, thus also reducing production, deposition, and consequent eutrophication due to nitrogen oxides associated with fossil fuel combustion. However, nitrogen and carbon GHG emissions from agriculture (such as N2O and CH4) are some of the most difficult to reduce. In the energy sector, humanity needs to perform one action: Stop burning fossil fuels. And, at least in principle, there are clean-energy alternatives. In agriculture, many different actions are required. There is no alternative to eating.
Nevertheless, we can begin to structure our thinking about solutions for the sector in a way that mirrors the fuel-switching solutions for other GHG sources—a rule of thumb that everyone from policy-makers to farmers, communities, and even children can comprehend and help put into practice.