It is a painful lesson of our time that the things we depend on to make our lives more comfortable can also kill us. Our addiction to fossils fuels is the obvious example, as we come to terms with the slow motion catastrophe of climate change. But we are addicted to nitrogen, too, in the fertilizers that feed us, and it now appears that the combination of climate change and nitrogen pollution is multiplying the possibilities for wrecking the world around us.
A new study in Science projects that climate change will increase the amount of nitrogen ending up in U.S. rivers and other waterways by 19 percent on average over the remainder of the century — and much more in hard-hit areas, notably the Mississippi-Atchafalaya River Basin (up 24 percent) and the Northeast (up 28 percent). That’s not counting likely increases in nitrogen inputs from more intensive agriculture, or from an increased human population.
Instead, Stanford University researcher Eva Sinha and her co-authors simply took historical records of nitrogen runoff as a result of rainstorms over the past few decades, recorded by the U.S. Geological Survey. Then, assuming for the sake of argument that there will be no change in the amount of nitrogen being added to the environment, they calculated how much additional nitrogen would be leached out of farm fields and washed down rivers solely because of extreme weather events and increased total rainfall predicted in most climate change scenarios. The bottom line: “Anticipated changes in future precipitation patterns alone will lead to large and robust increases in watershed-scale nitrogen fluxes by the end of the century for the business-as-usual scenario.”
But the business-as-usual scenario is of course already in trouble, even without climate change. Headlines have tended to fixate on the Gulf of Mexico “dead zone” produced by nitrogen flushed down the Mississippi River from the cornfields of the upper Midwest. (This year’s “dead zone” is the largest ever, the National Oceanic and Atmospheric Administration announced last week.) But the problem is already much broader than that, says senior author Anna M. Michalak, also of Stanford, citing a series of recent incidents caused by nitrogen pollution. Last summer, for instance, a 33-square-mile algae bloom caused Florida to declare a four-county state of emergency. Another closed the Dungeness crab fishery along half of the Washington State coast last year and affected other fisheries as far south as Mexico.