Earth System Impacts and Energy Use by the Food System

Human System Impacts on the Environment Within Food Systems

Figure 10.2.1. The collection, transport, and application to the soil of plant nutrients using animal manure (left), and the destructive effects of erosion from tillage on sloped land (right) are two human system impacts on the earth system.

Credit: Steven Vanek

Figure 10.2.2. Fertilizer production, like in this old print of a factory in Philadelphia, Pennsylvania, and a large new plant in India, represents a substantial contribution to the energy expenditure and greenhouse gas footprint of food production via modern agroecosystems.

Credits: top, Boston Public Library, used with permission via a creative commons license; bottom: used by permission through the Wikimedia Commons.

In modules one and two of this course, and most recently in this module, we represent food systems as coupled human-natural systems. Throughout the course, we have tried to emphasize the dramatic impacts that human food production has had and continues to have on earth's natural systems. Here are some examples from previous modules:

• Changing river basins to create irrigation systems
• Exposing soils to greater rates of erosion, and stabilizing some soils against erosion
• Domestication and development of new crop types, including transgenic engineering of new crop traits in the recent past
• Contributions of agriculture to greenhouse gas emissions that are warming planet earth and leading to climate change

Different types of food systems – global, smallholder, and alternative, as we summarized in module 10.1 -- may all impact the earth's natural systems in a different way and to different degrees. You may recognize on the short list of examples above that the impacts from these changes and the creation of agroecosystems by humans may have both positive and negative aspects. For example, irrigation and crop breeding both have as objectives increasing the productive potential of crops. They may carry other unforeseen consequences, such as depletion and collapse of water resources, changes in the dietary quality of food with domestication and breeding, and greater use of herbicides in the case of Roundup-ready crops. These human system actions within the food system improve production can be seen as the initial driving arrow as part of a human-natural system coupling (Fig. 10.2.3) and generally involve management, reorganization of the ecosystem, and energy and nutrient inputs (e.g. the use of fossil fuels to create fertilizers). The natural system then responds with positive and negative impacts on productivity and other natural system processes, which can include positive and negative consequences. These consequences eventually determine the level of sustainability of the food system. The massive extent of food systems and food production globally, within different types of food systems, translates into a large effect, or leverage, on the sustainability of human societies. To promote the sustainability of food systems, we must understand how food systems as a whole affect measures of sustainability. In this unit, we will first refer to the different human system impacts on natural systems, and then allow you to practice life-cycle assessment (LCA) to compare the energy use of two food production systems in the Andes and North America.

Figure 10.2.3. Human system impacts of food production activities. The human system reorganizes and provides energy and nutrient inputs to the natural system (1), which induces changes in natural system processes such as nutrient cycling, greenhouse gas emissions, and agrobiodiversity (2a). The changes in the natural system allow the human system to produce food but may also alter ecosystem services in harmful or unintended ways (2b: e.g. water pollution, global warming, and biodiversity changes in land and ocean systems).

Credit: Karl Zimmerer / Steven Vanek

Life Cycle Assessment (LCA): Measuring the Impacts of Systems in Multi-part Processes

Life Cycle Assessments

Life cycle assessments or life cycle analyses (LCAs) are defined as “a tool to analyze the potential environmental impacts of products at all stages in their life cycle” (International Standards Organization). Analogous to the food supply chain activity you completed in module 10.1, LCAs follow products (foods and otherwise) from production, through transport and assembly steps, to the consumption or operation of the product, and in some cases even its disposal. In contrast to the supply chain descriptions in module 10.1, at each of these stages of production, transport, consumption, and disposal, LCAs keep a running total of environmental costs or impacts of the product. Common impacts that are tracked by LCAs across product life cycles are greenhouse gas emissions, water pollution impacts, and energy use. As such LCAs are a key tool in analyzing the impacts of human on natural earth surface systems within the coupled natural-human food system (Fig. 10.2.3). LCAs require some careful thinking about where to draw the boundaries of the system for considering the life cycle of a product. For example, an LCA devoted to carrots would probably include the energy required to operate the refrigerated truck used to transport the carrots but not the energy needed to make the truck. Also, many LCAs are “cradle to grave” and include both impacts of all raw materials used in production as well as disposal impacts for the product, but some do not focus on the entire life cycle and assess other segments of the lifecycle such as “cradle to farm-gate” or “cradle to plate” in the case of food products.

Life cycle analyses are an excellent way of putting into practice a geosciences "habit of mind" of using systems thinking. Because food systems are complex, we think about a way to measure its performance and then explore all the linkages in the system within that single metric or measurement parameter (see module 1.2 for a discussion of complex systems behavior). That is, we don't content ourselves with just thinking about a crop plant in a field, the entire farm field, or the highway where foods are transported; we go several levels up to measure impacts along the entire pathway or web of interacting system parts. Along the way, it is likely that we will start to think in new ways about the linkages between parts of the system, about the most important contributions to impact, or about previously hidden factors or unexpected outcomes that explain the performance of the system.

Using LCAs, Part One: Comparing Costs and Impacts

Life cycle assessments are often used in two important ways. The first is to compare the costs or impacts of different products or production systems in a rigorous way, seen in Fig. 10.2.4 which compares the phosphorus water pollution resulting from three ways of producing pork meat in France (Basset-Mens and Van Der Werf, 2005). This “cradle to farm-gate” pork LCA includes the cropping used to produced pig feed as well as the animal raising methods at pig farms that use three different standard methods. In this example, two different ways of expressing LCA results show how different messages can emerge depending on how results are presented. The graph at left shows the impacts at a per-area of land used basis (per hectare), while the graph at right expresses the impact as a per-kg of food produced, which means that if a production method yields more on a per-area basis, its impact can be reduced compared to one with less productivity per hectare. Organic and red-label humane methods with straw-bedded barns pollute less on a per-hectare basis, but the organic methods are not less polluting than the conventional treatments on a per-kg of pig basis because more area is needed to both raise the pigs and grow the crops for feed in the organic system. Therefore if demand (in kg pork) remains the same for pigs while consumers switch from conventional to organic pork, total water pollution from phosphorus in pig production is unlikely to decline, at least according to this study. Rather, the red-label option seems to be able to shrink pollution per kg of pork consumed in the food system. Meanwhile, if you limited your viewpoint to a single watershed with a delimited area, you would say that both the red-label and organic methods reduce pollution. Despite some of the benefits of organic management generally, in reducing toxins in the environment and building soil quality (for example), this study can give us some pause in thinking about the particular system we are talking about (e.g. organic hog production versus organic apple production, for example) and the need to respect specific case analyses and the measures used in LCA analysis. When we talk about a whole food system, it may be best to employ a per-kg of food produced approach.

Figure 10.2.4. Results of a life cycle assessment for eutrophication impacts (water pollution, see modules 3 and 4; in this case, via phosphorus or P runoff into surface waterways of pork production under different standard methods in France: European Union (EU) standard best conventional methods using confinement of hogs; a "red label" which denotes a defined-origin producers' standard using more humane methods and sustainable but non-organic crop practices, and organic standard methods including more humane treatment and organically produced crops. (data adapted from Basset-Mens and Van Der Werf, 2005).

Credit: Steven Vanek

Using LCAs, Part Two: Assessing Hot Spots

The second main way of using LCA is to assess which steps or process inputs in the production, consumption, and disposal of a product are most responsible for human negative impacts of practices. These “hot spots” in the analysis can then be the focus for better measurement to confirm the findings of the LCA and/or innovations in practices that eliminate these practices or limit their impact. One type of LCA uses the common measure of external energy inputs for food production (i.e., those not related to solar energy that is used by plants "for free") to analyze one aspect of the sustainability of food production. These energy inputs are visualized in Figure 10.2.5.

Figure 10.2.5. Principal human-managed energy inputs involved in food production, in addition to resources of soil and water as well as the solar energy captured by plants. Energy expended in irrigating crops, and in the growing of seed, would be additional flows that might be especially important in other systems. These energy flows are summed up using an LCA approach, noting which ones account for most of the impact, creating "hot spots" that should be researched further and targeted to increase efficiency and reduce the impacts of food production.

Credit: Steven Vanek

Dissecting an LCA

An LCA for energy use is illustrated below in Fig. 10.2.6 which shows the comparison of total energy used in different crop production practices in a long-term trial of farming practices in Switzerland. This graph shows the energy used in food production in two formats: stacked colored bars as kilowatt-hours (kWh) energy equivalent per land area under production (i.e. per Ha or 100 x 100 m area) of food production, and also as a total watt-hours (Wh) per kg of food produced (dark green lines and points above the stacked bars).

It's worth considering these results and the units used in more detail. First, for comparison, a typical U.S. home uses about 72 kWh per day for heating, cooling, and electricity, if we boil all these energy uses down to one energy equivalent^* (calculations based on the U.S. Energy Information Administration, 2009 data [4]). Some further "ballpark" or rough calculations allow us to see that the fertilizer-based system (bar at right) uses a total of about 100 days of mean household energy^**to produce food on one hectare in a year (per year), while the organic system (bar at left) uses a little over half this amount of energy. Meanwhile, if we express this daily household energy use as the energy used for food per kg of food, the 72 kWh become 94 kg of food in the fertilizer-based case at right, and 144 kg of food in the organic management case at left ^***. Expressing LCA results as energy per land area and energy per kg food produced are common approaches, analogous to the pollution impact analysis on the previous page. In the summative assessment on the next page, you will use an LCA to calculate energy inputs per kg of potato production in two systems.

* That is the amount of heat and light given off by 30 100-watt light bulbs burning for 24 hours.

** That is, about 7200 kWh (height of rightmost split bar on the left axis showing energy use per hectare), divided by about 72 kWh household use per day, which is equal to 100 days.

*** Dividing 72 kWh by the energy amounts per kg from the green point+line data above the stacked bars, e.g. 72 kWh / 0.77 kWh per kg or 93 kg food for the fertilizer based-case, and 72 kWh / 0.50 kWh per kg, or 144 kg of food, for the organic case.

Figure 10.2.6. Results from a life-cycle analysis on energy use equivalents to compare three farming methods growing a variety of food crops in a long-term research trial (DOK Trial, Therwil, Switzerland). The left Y-axis and stacked colored bars give the energy use per land area (i.e. per Ha or 100 x 100 m land area) and might be helpful to know if we have the total production land area of a farm or region. Meanwhile, the plotted points above each stack and right y-axis give the energy use per kg of dry matter of crops produced, which may be a more useful measure for a food system where we want to adjust for the productivity of different food systems. It is notable that the largest differences between the three systems derive from in the energy used to manufacture chemical fertilizer (yellow bars). Figure adapted from data cited in Nemecek, T. 2005. Life Cycle Assessment of Agricultural Systems: Introduction [5].

Credit: Adapted from data in the study cited in caption (Steven Vanek)

Fertilizer Use as a "Hot Spot" in the Analysis

Two additional observations: first, in this LCA there emerged large differences in energy use that have to do almost completely with the energy used to produce chemical fertilizer, especially of nitrogen fertilizers like those produced in the large fertilizer plant in India shown in Fig. 10.2.2. Energy inputs to fertilizer production are especially high for nitrogen fertilizer because it takes a great deal of energy to fix inert nitrogen in the atmosphere (N₂) into reactive forms like ammonium and nitrate that can be easily taken up by crops (see module 5 and other previous modules). Fertilizer use emerges as a "hot spot" in this analysis and might prompt managers or policymakers to work towards reducing fertilizer use by incorporating aspects of the organic and manure-based system into the more conventional, fertilizer-based system. Many energy inputs in agriculture, such as these fertilizer inputs or tractor fuel that are tallied in the LCA above, are important to consider because they represent non-renewable fossil fuel energy sources that contribute to greenhouse gas emissions and anthropogenic climate change through the release of carbon dioxide. The LCA thus helps to measure natural system impacts and sustainability of food systems. Second, this LCA used energy as a yardstick to measure the impact of food production. As we will note for your summative assessment, such an LCA using energy inputs is only ONE measure of sustainability, and may not capture other measures of sustainability, like forest clearing needed to establish agroecosystems, runoff of nutrients that contribute to dead zones, pesticide effects on beneficial insects like pollinators, or whether farming practices provide sustained income and other livelihoods to farmers. As an example of using a different yardstick for LCAs, consider the emissions of greenhouse gases (GHG) by different pork production systems on the previous page, in which the organic management system, in fact, had higher potential to pollute waterways with phosphorus runoff per kg of pork produced, than either conventional or "best practices" red label standard in the European Union. This result contrasts with the favorable result shown on this page for organic management when energy inputs were used as a yardstick.

Knowledge Check: Earth System Impacts and Life Cycle Analysis

Summative Assessment: Life Cycle Assessment (LCA) of Energy Use in Potato Production in Smallholder Andean and North American Production Systems

Instructions

This assignment has been broken down into three steps. First, you need to understand the LCA Spreadsheet, next you will need to complete the spreadsheet and finally you will complete the Summative Assessment Worksheet using the results of the completed spreadsheet. Please read all of the instructions very carefully. They are presented in the next three pages.

Files to Download

Energy Input LCA Activity Spreadsheet [6]
Summative Assessment Worksheet [7]

Submitting Your Assignment

Please complete the Module 10 Summative Assessment in Canvas.