While it doesn't get the same amount of press as carbon dioxide, nitrogen pollution ranks among the major environmental and public health challenges we face today - and conventional agricultural production is mostly to blame. We recently spoke with David Kanter about the problems caused by nitrogen pollution and how we can better manage this critical resource. David, an Assistant Professor in the Department of Environmental Studies at New York University, is in the process of developing a project with Jeffrey Sachs, director of The Earth Institute at Columbia University, focused on translating the emerging science on nitrogen pollution into actionable policy recommendations to ensure more efficient use of nitrogen fertilizer.
Tell us about your background/expertise.
I'm half Swedish, half English and grew up in Belgium. As a teen I got caught up in the excitement around dealing with climate change. I liked how it needed an interdisciplinary perspective. So I studied Chemistry and Law in undergrad (at University of Bristol in the UK) and worked for Greenpeace during that time and afterwards in the lead up to the 2009 Copenhagen talks. My focus there was on the Montreal Protocol, the international ozone agreement (and probably the most successful international environmental agreement ever), and how it could be used to help fight climate change.
I wanted to study that issue more during my PhD at Princeton (in the Science, Technology and Environmental Policy program at the Woodrow Wilson School for Public and International Affairs), and a few months after I started a paper came out showing that nitrous oxide was not only the third most important greenhouse gas, but also the largest remaining threat to the ozone layer. Nitrous oxide is also an important part of the nitrogen cycle. So a central question of my PhD became "how and to what extent could the Montreal Protocol control nitrous oxide"? Answering that question forced me into the complexities of the nitrogen cycle, and that's when I started thinking more broadly about nitrogen pollution and how to address it.
Nitrogen pollution is one of the major domestic and global environmental problems we face today. Tell us why?
Nitrogen pollution is a unique environmental issue. On the one hand, nitrogen is an essential resource: it's the fundamental building block of proteins, amino acids and DNA, and it fuels photosynthesis - in short, it's central to life itself. Moreover, our ability to manufacture nitrogen fertilizer at an industrial scale (known as the Haber-Bosch process) has allowed us to vastly increase global food production without an equivalent increase in the amount of land used to grow it. Today, half the world's population is fed with food grown using industrially manufactured nitrogen fertilizer (the remainder uses manure and nitrogen-fixing legumes such as soybeans). However, here's the problem: about half the nitrogen that we put on our agricultural land is lost to the environment. And the unique chemistry of the nitrogen cycle means that one atom of nitrogen can easily travel between different forms, each with a specific impact on the environment and human health.
Reducing meat consumption across society as a whole would do more to reduce nitrogen losses than most measures.
For example, one atom of nitrogen may start out in fertilizer, before being emitted as ammonia and contributing to air pollution; it may then be deposited into a waterway as nitrate, polluting aquatic ecosystems and creating coastal dead zones; that same atom of nitrogen can then be transformed into nitrous oxide, exacerbating climate change and stratospheric ozone depletion. This phenomenon is commonly referred to as the nitrogen cascade, and illustrates how nitrogen pollution contributes to a suite of environmental and human health impacts. A recent study of all the major environmental threats we face (climate change, fresh water pollution, etc.) classified nitrogen pollution as one of only two issues (the other being biodiversity) where humanity has already exceeded a safe operating space, or planetary boundary.
It should also be noted that while agriculture accounts for about 80 percent of the nitrogen pollution problem, the remaining 20 percent comes from non-agricultural sources such as transportation, fossil fuel burning and wastewater.
How does our food system factor in to this global problem? Where are we specifically seeing our inefficient use of nitrogen fertilizer play out?
So while it's true that about half of the nitrogen we put on our agricultural land is lost to the environment, that number masks a lot of variation across different countries and foodstuffs. For example, corn is the single largest consumer of agricultural nitrogen in the US. And meat production is a much more inefficient user of nitrogen than crop production. Of the 50 percent that is taken up by crops, only 10 percent is recovered in chickens, 5 percent in pigs and 3 percent in beef. And then certain countries use much more fertilizer than is required, often driven by artificially low fertilizer prices as a result of government subsidies. For example, a recent survey of over 4,000 wheat farmers in China showed them applying close to 200 kilograms of nitrogen per hectare on average, more than double the US average. Fruit and vegetable farmers were applying over 500 kilograms of nitrogen per hectare on average. Such high application rates inevitably lead to excess nitrogen in the soil, which is the main source of the nitrogen pollution problem in agriculture.
What can be done to address nitrogen pollution from the agricultural sector?
The goal of addressing agricultural nitrogen pollution is simple (even if the implementation is not): we need to better synchronize when nitrogen is in the soil, with when plants actually need it. And there are several strategies for doing that; some work within our current system of industrial agriculture; others require a more fundamental transformation of how we produce food.
One strategy for our current system involves farmers learning how to better manage nitrogen themselves: either splitting up fertilizer application over the course of the growing season instead of dumping it on all at once; or using GPS and other technologies to identify more precisely what parts of their land need more nitrogen instead of applying the same amount everywhere. Another strategy is to use new products known as enhanced-efficiency fertilizers, which either delay the release of nitrogen in the soil or make it stay in the soil for a longer period of time, increasing the likelihood that it will get taken up by a crop. When it comes to meat production, there are a number of feeding practices that can improve the nitrogen conversion from feed to meat, and products that can be applied to manure once it's in storage or on the field that reduce nitrogen losses.
While these approaches are by no means "easy" to implement (otherwise they would have been already), they do not require a fundamental transformation of the agricultural system. Examples of strategies that require such a transformation involve better integration of livestock and crop production, such that the nitrogen excreted from one source (livestock) can be immediately used by another (crops), further reducing the potential for losses along the nitrogen cascade. Polyface Farm, made famous by Michael Pollan's book "The Omnivore's Dilemma" is a popular example of this. More broadly, reducing meat consumption across society as a whole would do more to reduce nitrogen losses than most measures (see below on the role of consumers). Other more transformative options include massively increasing the acreage devoted to legumes, which can fix their own nitrogen from the atmosphere and reduce the need for fertilizer.
Tell us about the research you are involved in and the project you have helped to develop to assist policymakers in tackling the nitrogen pollution problem.
The common thread throughout my research is trying to translate the emerging science on nitrogen into actionable policy recommendations. So I've been working with legal scholars to identify the most promising legal pathways for managing nitrous oxide in the US, and quantifying the economic and environmental impacts of following them. I'm also part of a new initiative involving around a hundred or so scientists and policy experts that's trying to develop an IPCC-equivalent for nitrogen - a science platform for policy-makers concerned about nitrogen. And the project I'm most excited about is focused on using local teams of experts in regions across the world to set targets for reducing nitrogen pollution and develop strategies and policies to achieve those targets that are best-suited to those regions. The ultimate goal is to have regionally distinct pathways for reaching the planetary boundary for nitrogen, giving policy-makers a clearer path forward.
What grade would you give the US in addressing this problem?
Probably a B minus. US policy on certain isolated aspects of the nitrogen issue have been successful. For example, emissions of nitrogen oxides (important air pollutants) from cars and power plants have decreased substantially over the past two decades thanks to the Clean Air Act. In the agricultural sector, however, even though fertilizer application rates have stabilized and crop yields have increased (indicating an increase in the efficiency of nitrogen use), nitrogen losses have remained stubbornly high. There are still massive dead zones in the Gulf of Mexico and the Great Lakes every year due to nitrogen leaching which is a major driver of toxic algal blooms; ammonia emissions are still impacting local air quality across the US; and nitrous oxide is still responsible for about six percent of the US carbon footprint.
More could be done, but unfortunately almost all of US agricultural policy focused on the environment is voluntary. Instead of more stringent regulatory instruments, the US relies on incentive-based systems that only a small proportion of US farmers participate in. This limits the potential for reducing nitrogen pollution from agriculture in the US. One policy option would be to apply the fuel-efficiency standard approach that President Obama used for the automobile industry on the fertilizer industry. So instead of telling farmers to use more of product A instead of B, or to learn practice X instead of Y, the fertilizer industry (which is dominated by just four companies in North America) would be mandated to increase the proportion of enhanced efficiency fertilizers in their products. Such a policy would be easier to implement and monitor, as we would be focusing on four fertilizer companies, rather than millions of farmers.
Is there a role for the general public/consumers to play?
Yes, there are several things that the general public can do - some to do with personal lifestyle choices, others related to political engagement. Perhaps the most important thing an individual consumer can do is to reduce their meat consumption, given how inefficient the livestock sector is in using nitrogen. There are already several compelling reasons to reduce meat consumption, whether it's because of the climate impacts, the threats to biodiversity or the ethics of it. Nitrogen adds yet another dimension to the argument.
Reducing food waste is also important. A recent investigation by the Guardian newspaper suggested that about 50 percent of the food bought in the US was wasted. So we're essentially flipping a coin right now as to whether the food we buy ends up in our bodies. We need to improve on that front, particularly given that the UN Food and Agricultural Organization says we need to double food production by 2050 in order to feed the world's growing population.
In terms of political engagement, the Paris Climate Agreement recently called for the world to stay "well below" a two degree Celsius global temperature increase. If we're to have any shot at that, all greenhouse gases need to be on the table, not just carbon dioxide. This includes nitrous oxide. And my work has shown that, when done well, the indirect benefits of reducing nitrous oxide (from reduced nitrate losses, and emissions of ammonia and nitrogen oxides) often outweigh the direct climate and ozone benefits.
Who do you look to for inspiration/who inspires you?
I particularly admire people who can act as "knowledge brokers" between academia and the policy world - which is harder than it looks. Someone who has the credibility in academic circles, who is well regarded, publishes in good journals etc. but has the ability to distill complex information and communicate it in a way that is clear, compelling and relevant to policy-makers' concerns. That's a rare combo, to be able to move seamlessly between those two very different worlds.
For climate change you have people like Steve Schneider (who unfortunately passed away several years ago), Michael Oppenheimer, Heidi Cullen and Bob Watson. The most compelling science communicator in my mind across all fields is Neil deGrasse Tyson (Director of the Hayden Planetarium in NYC). I think we're still looking for someone like that for nitrogen.
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