How do we measure agricultural sustainability?
The idea that the US agricultural system is broken and getting steadily worse is often treated as self-evident in environmental circles. After all, the environmental impacts of US agriculture are massive. Farming spans 40% of US land and produces 9% percent of our greenhouse gas (GHG) emissions.
But this reasoning confuses scale with sustainability. Measures of total impacts are determined not just by how farmers produce food, but also by how much they must produce to meet consumer demand. The impacts of US farming are huge in large part because we produce a lot of food — the total value of US agricultural production has increased by over 125% since 1961 and is around 11 times greater than the UK’s total value of production.
Nonetheless, such statistics are often proffered as conclusive evidence that US farming is broken and in need of a revolution, with critics often calling for mass adoption of specific practices such as organic farming, cover cropping, or grass-fed cattle grazing. But a fixation with practices supplants an empirical approach to the question of whether the impacts of US agricultural production are indeed headed in the wrong direction.
If we care about agricultural sustainability, we should care enough to measure it, holding constant confounding trends that say nothing about the environmental performance of food production itself. We can accomplish this by tracking intensity measures. Unlike total impacts, intensity measures — the environmental impact or quantity of inputs per unit of agricultural production — isolate the environmental performance of farmers and other agricultural producers.
Once we hone in on the environmental intensity of agricultural production, we can see that US farmers have steadily been improving for the last half-century.
However much better we might think agricultural sustainability would be in a radically different vision of food production, intellectual honesty dictates that we acknowledge what has actually been occurring, and that the further improvements we desire would continue or accelerate, rather than reverse, the historical trajectory.
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Among many dramatic improvements in US environmental intensity, reductions in land use intensity — the amount of land used to produce each unit of food — stand out. Since 1961 the amount of land required to grow a ton of wheat has fallen by nearly 50 percent, and we’ve witnessed similar trends for corn, soy, and rice. Growing more food on less land means less forestland converted to farmland and less greenhouse gas emissions released in the process. And land-use change pressures are an immediate concern — in the absence of yield gains, WRI predicts that agriculture’s global land footprint would expand by 3.3 billion hectares by 2050. Because US agriculture is less land intensive than farming in almost every other country, continuing to increase yields and concentrating more food production in the US could reduce global land-use change.
Greenhouse gas emissions trends are another sustainability success story. While total US greenhouse gas emissions from agriculture have risen over 10 percent since 1990, emissions per kilogram of food have dramatically fallen for beef, pork, cow milk, chicken, and other foods in part thanks to new technologies, rising yields, and adoption of soil management best practices. The environmental benefits of more efficient agricultural production are substantial — if the GHG intensity of US beef production had not improved since 1961, for example, today’s level of beef production would generate 50% more GHG emissions, chicken production around 100% more, and milk production over 200% more.
Many other environmental metrics have improved as well. Water use intensity, or water use per dollar of foodWe use food as shorthand here for food, feed, fiber, and fuel, acknowledging that much agricultural production is not for food production.produced, has fallen for decades — by almost 90 percent since 1960. That is, were the water use intensity still the same as it was in 1960, today’s agricultural GDP would require almost 900 billion gallons of water per day rather than the current 120 billion gallons. Measures of soil erosion per acre and per dollar of food produced have also fallen — by around 60% and 65% for water and wind erosion, respectively.
Other intensity metrics have not fallen as sharply but still show signs of modest improvement. For example, nitrogen loss per unit of production, which is responsible for nitrous oxide emissions and harmful runoff, has worsened over time but appears to be levelling off. And despite overall increases in its nitrogen use intensity, US agriculture still performs more than 35% better than the global average by this metric.
Herbicide use is another story of mixed success. While the quantity of herbicides applied per acre has increased, the toxicity hazard of herbicide applications for many crops has declined or generally remained constant. Mammalian toxicity of herbicides for soy and spring wheat, for instance, has dramatically fallen since 1990, in large part due to phasing out the most toxic herbicides in favor of less harmful substitutes.
By many measures, then, the environmental sustainability of US agricultural production has steadily, and often steeply, risen over the last half-century. American farmers have boosted production while limiting resource use and impacts, and the environmental benefits, too often overlooked, have been vast.
Yet these past improvements do not justify complacency.
Indeed, there is cause for alarm. The improvements we’ve witnessed have been driven, in part, by publicly funded research and development (R&D), which has seen its funding decline by almost 30 percent since 2002. And since R&D’s effects are delayed, the steady sustainability trends we’ve witnessed since the turn of the century might begin to exhibit signs of faltering growth in the near future. This is especially concerning, since, as the world’s population grows larger and wealthier, preventing agriculture’s impacts from precipitously rising will require not just maintaining, but accelerating environmental intensity improvements.