In the scientific community, it is widely accepted that the global climate is changing, and that human activities are a principal cause. Many human activities produce “greenhouse gases.” These transparent gases are present at trace concentrations in the Earth’s lower atmosphere. They have the unique quality of trapping heat there. This trapped heat is driving many of the recent changes in the Earth’s climate, including rising global temperatures.
Figure 1. USA greenhouse gas emissions, by sector. From Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2014, https://www3.epa.gov/climatechange/Downloads/ghgemissions/US-GHG-Inventory-2016-Main-Text.pdf. “MMT CO2 Eq” refers to million metric tons of carbon dioxide equivalents.
Figure 1 illustrates greenhouse gas emissions in the USA, by economic sector. Sometimes, agriculture is unfairly blamed as a leading cause of global warming. Certainly, agriculture is an important source of greenhouse gases. However, Figure 1 illustrates how other sectors of our economy are even more important sources. Ultimately, we must address emissions from all sources.
Policymakers worldwide are seeking ways to reduce emissions of greenhouse gases, so that we can reduce the disruptive impacts of climate change on water supplies, food production, human health, and extreme weather. Since carbon dioxide is the most important greenhouse gas, policymakers often speak of reducing our “carbon footprint.”
U.S. producers have excelled at getting more yield from an acre of land. This is called intensification. For example, astonishing increases in grain yields have been achieved in the U.S. (Figure 2) and yields show no indication yet of slowing. Remarkable yield increases have been achieved in horticultural crops, as well (Figure 3).
Figure 2. Trend-line for yield of field corn in the USA since 1900 (data source http://quickstats.nass.usda.gov/).
Figure 3. Trend-line for yield of fresh-market tomato in the USA since 1960 (data source http://quickstats.nass.usda.gov/).
Here is how this crop intensification relates to greenhouse gas emissions. Between 1980 and 2011:
- U.S. corn producers emitted 36% less greenhouse gases to produce a bushel of corn (Field to Market, 2012).
- Cotton producers emitted 22% less greenhouse gases to produce a bale of cotton.
- A 22% reduction in greenhouse gases per hundredweight of potatoes was observed.
- Rice and soybean producers achieved reductions of 38% and 49% in greenhouse gases per unit of production.
- Over the study period, wheat production emitted 2% fewer greenhouse gases per bushel produced.
There is no question that U.S. crop production does emit significant amounts of greenhouse gases. However, an important way to evaluate carbon emissions from crop production is to compare them to the unit of crop production, because the unit of production is what is traded and consumed. By that standard, U.S. producers excel, because of efficiencies of scale and high-yield production.
Our high-production agriculture stands in contrast to the situation in many developing countries, where crop yields are quite a bit lower. In such countries, the path to producing more food may include bringing more land under cultivation. This can increase the carbon footprint per unit of production by as much as three times.
Pound-for-pound of food produced, U.S. farmers have significantly reduced the carbon footprint of food production. However, crop production does emit greenhouse gases, and knowledgeable experts agree we must reduce our carbon footprint further. Therefore, the challenge before us is, for every acre of land cultivated, we must grow as much food as is reasonably possible, with as little environmental impact as possible, including carbon emissions.
While U.S. agriculture has served us very well over the years in providing abundant, safe and wholesome food, more and more farm organizations recognize that we must do more to reduce the carbon emissions of producing the food we want and need. It is a significant challenge, but one we must address in order to do right by our descendants.
- Balmford et al. 2015. Land for Food & Land for Nature? Dædalus, the Journal of the American Academy of Arts & Sciences. doi:10.1162/DAED_a_00354
- Field to Market (2012). Environmental and Socioeconomic Indicators for Measuring Outcomes of On-Farm Agricultural Production in the United States: Second Report, (Version 2), December 2012. Available at: fieldtomarket.org
- Foley et al, 2011. Solutions for a cultivated planet. Nature, Volume 478, pages 337-342, http://bit.ly/MdA5yo.
- Grassini and Cassman, 2012. High-yield maize with large net energy yield and small global warming intensity, Proceedings of the National Academy of Sciences, Volume 109. Pages 1074-1079, http://bit.ly/KhTQCe.
- Stevenson et al, 2013. Green Revolution research saved an estimated 18 to 27 million hectares from being brought into agricultural production. Proceedings of the National Academy of Sciences, Volume 110, pages 8363-8368, http://bit.ly/12x7o3f
- Tilman et al, 2011. Global food demand and the sustainable intensification of agriculture. Proceedings of the National Academy of Sciences, Volume 108, pages 20260-20264, http://bit.ly/KfNC3L.
- West et al, 2010. Trading carbon for food: Global comparison of carbon stocks vs. crop yields on agricultural land. Proceedings of the National Academy of Sciences, Volume 107, pages 19645–19648, http://bit.ly/KcjEEu.
Selected content in this publication was originally published in the Extension publication, Intensification Has Reduced Carbon Footprint of U.S. Crop Production.