Ask the Okala experts

When modeling the life cycle environmental performance of products and services, some people account for process flows – energy use, water use and solid waste production. Others account for environmental impacts – such as global warming potential, human toxicity and ecotoxicity, water pollution, ozone layer depletion, and smog production. Differences between these measurable groups may seem subtle, but they have significant implications for our ability to protect natural ecology and human health.

Process flows
Non-scientists quickly comprehend the idea of process flows. Embodied energy, water use and solid waste production are relatively self-explanatory concepts. As a rough and simple metric – they indicate the quantity of resources associated with the production of a material or process, and they echo the common idea that material, energy and waste flows are proportional to environmental impacts. This generalization can, however, lead to erroneous conclusions. A closer look reveals some of the paradoxes inherent in measuring process flows in the pursuit of making ‘greener’ products.

Solid waste, most people assume, is the debris that is hauled away in our garbage cans. That waste is part of the total solid waste flow, but a greater amount often comes from the factories where the products are manufactured. Mining processes that separate metal from rock ore generate an even greater stream of solid waste. Solid waste is not an environmental problem per se. Its impact on the environment is the real issue, if toxic emissions to ground or surface water affect human or ecological health, or wild habitats are destroyed to make space for landfills. Assessing the quantity of a solid waste stream alone can be misleading.

Potable water is certainly becoming more scarce on a global level; it is a much more critical problem in some areas than others. In arid areas (like sub-Saharan Africa and the US Southwest), water is at much more of a premium than in others (like Northern Europe and the US Northeast). Scientists (including the US EPA developers of TRACI, the impact method used in the Okala Impact Factors) are trying to make practical regional assessment methods for water. These impact methods may be called ’fresh water depletion‘– but it is challenging to develop such regional methods because LCA is a global methodology. We currently lack accounting methods that specify if the water is coming from a depleting source (like a dropping aquifer) or a sustainable source (like a lake that is replenished annually). Until we have such methods – treating all water as if it were depleting can penalize water use in areas where it is not a problem.

Embodied energy is sometimes used as a surrogate for the ecological footprint of a system. But what type of energy is embodied in a material or process? Coal electricity is dirtier than natural gas electricity, which is dirtier than wind electricity, which is quite different from nuclear electricity. Then there is clean solar thermal energy, heat from fuel oil boilers, not to mention the different impacts from burning gasoline, diesel and various biofuels (which could be destroying tropical habitats). These disparate sources for what can be accounted for in embodied energy mask the hugely divergent environmental impacts that these various energy sources create.

Ecological and human health impacts
Environmental impact categories are more specific than process flows. They model damage to natural ecology and human health more precisely than material flows because they model resource depletion processes and complex chemical emission pathways with the subsequent reactions that cause specific impacts to ecology and human health. For example, the impact categories measured in the TRACI characterization method used in the Okala Impact Factors are listed below.

To understand how process flows can oversimplify complex ecological and human health phenomena, let us consider an example: energy. We can measure a material’s embodied energy for its production from extraction in nature and all the following processing steps for the final material (measured in kilowatt-hours or other equivalent units per pound of material). For the sake of clarity, let us assume the material has an embodied energy of 1kw-hr/lb.

Environmental impacts of 1 kilowatt-hour of energy from various sources in Okala millipoints

Above we see the specific environmental impacts created in the production of one kilowatt-hour of four types of energy: windmill generated electricity, heat energy from a natural gas industrial boiler, electricity from multi-junction silicon photovoltaic panels on a slanted roof, and electricity from a nuclear reactor.

This is just a minor sample of all of the energy sources that are available, but it indicates the significant differences in the scale of each impact category that various energy sources create. In many, if not most cases, the energy source will have a greater effect on the total impact than the amount of embodied energy.

So, in the majority of cases, if you want to design greener products and more accurately protect the health of natural ecology and humans, environmental impact categories are more accurate and useful in describing these impacts than process flows.