Choice 1: Environmental Indicators
There are a wide range of environmental impacts that can be assessed. However, it's not always necessary to try to cover many, or even some, of these impacts if you're mainly interested in one impact measure, or environmental indicator. For instance, there's a lot of attention on greenhouse gas (GHG) emissions these days, due to their association with climate change. If the carbon footprint resulting from these emissions is the only impact your organization or your customers are focused on, it would be unnecessary to spend time assessing impacts on such things as air quality or human toxicity; measuring your product's carbon footprint would suffice. So, step one is to determine which impacts should be measured based on the purpose of the assessment and how its data will be used.
Five Categories of Impact
How to choose among the dozens of different types of environmental impacts? We'll start with grouping some commonly used environmental impact categories into five major domains:
1. natural resource depletion,
2. air impacts,
3. terrestrial & aquatic impacts,
4. climate effects, and
This section will describe these different environmental effects that Priscilla and Tom can choose to measure.
Natural Resource Depletion
This first domain reflects the many ways human activity uses up the Earth's natural resources. "Depletion" means that those resources are no longer available for further use in their highest-value forms.
A water "footprint" primarily refers to the amount of fresh water being used or consumed which then must be processed back to its fresh state (water quality issues are covered by other impact categories). Water is the only resource that is both renewable and finite. All of the water that was ever on Earth is still on Earth, but the breakdown of its location, physical state (water, vapor or ice), and salinity can limit its usefulness as a resource. In fact, after oil, many people believe that water will become the resource with the most highly valued access rights, which has significant social and environmental-justice implications.
Mineral deposits can't be renewed. Once a mineral deposit (like iron ore) is mined, it doesn't return to the earth as ore, no matter how much it's reused or recycled. There's only a finite amount of each mineral, so any used now will not be available for future generations to mine.
Land can't be depleted, really (ground pollution is covered later), but since a given acre can only be used for a limited number of purposes, land scarcity can be a real issue. Land can also become unusable, or at least less valuable, due to physical changes such as erosion.
A decrease in available land can impact a wide variety of systems, including agriculture, civilization, and biodiversity – the amount and variety of life that the land can support.
While there are a variety of non-renewable natural resources used for energy, the ones that usually get the most attention are oil, coal, and natural gas. This non-renewable energy impact includes the energy (electricity or fuels) used during the product's manufacture and use, and can even go one step further to include the upstream energy required to obtain and process the energy consumed in the product's lifecycle. Efficiencies in energy conversion (e.g. power, heat, steam, etc.) can also be factored in. The non-renewable energy demand can also include a measure of the embodied energy of the materials—that is, the energy that would be released if the product were burned.
The Earth is wrapped in a layer of gases mixed in proportions necessary to sustain life on the planet. There are several ways humans affect those proportions, with far-reaching results. (Effects to the climate are included in a separate domain.)
Burning fuels creates sulfur dioxide, nitrous oxides, hydroflouric acid, ammonia, and other acidic air emissions. This causes an increase in the acidity of rainwater, which in turn acidifies lakes and soil. These acids can make the land and water toxic for plants and aquatic life, and can leach life-sustaining minerals from the soil. Acid rain can also slowly dissolve manmade building materials, such as concrete—or these statues seen here.
Most people are very familiar with this impact--especially when it's called by its common name of "smog." Caused by the emission of air pollutants such as non-methane hydrocarbons, this effect results in decreased visibility, eye irritation, respiratory tract and lung irritation, and vegetation damage.
Ozone Layer Depletion
Not long ago, the holes growing in the ozone layer were the top environmental concern. While quick action has slowed, and in some cases reversed, the damage, ozone layer depletion is still a concern. Caused primarily by the emission of chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), halons, and methyl bromide (CH3Br), the thinning of the atmosphere's ozone layer allows increased ultraviolet radiation to reach the earth. This radiation can cause cancer in animals and decreased plant and algae viability.
Terrestrial & Aquatic Impacts
Several types of impacts directly affect land and water quality.
Eutrophication occurs when an overabundance of plant nutrients are added to a water ecosystem. Nitrogen and phosphorous from wastewater and agricultural fertilizers causes an algal bloom (explosive growth of algae), which then depletes the water of dissolved oxygen—a situation known as hypoxia--resulting in the suffocation of aquatic life.
While eutrophication occurs due to an excess of nutrients, ecotoxicity results from the presence of poisons in the water. This is generally caused by chemicals being dumped or seeping into lakes and rivers. It results in decreased aquatic plant and insect production and biodiversity, as well as impacting water drinkability.
Toxins present in soil cause decreases in wildlife and plant production and biodiversity. While some of these toxins may be introduced from airborne or aquatic sources, many are the result of direct human application or through leaching from industrial processes or waste accumulations.
The global climate is the result of myriad interacting systems. In many ways all of the other impacts have some influence over the climate. However, one climate effect in particular has been identified as a key factor in shaping the future of life on Earth. Climate change, sometimes called global warming, is one of the most commonly identified impacts of interest.
Climate Change/Global Warming
Carbon dioxide (CO2), methane (CH4), and other so-called greenhouse gases resulting from burning fossil fuels accumulate in the atmosphere, trapping solar heat which in turn increases the earth's average temperature. A product's climate change impact is often referred to as its "carbon footprint" because global warming potential is usually measured in units of carbon dioxide equivalent (CO2e). It is widely understood that global warming is the cause of such problems as loss of glaciers, extinction of species, soil moisture loss, changes in wind and ocean patterns, and more extreme weather, among others.
While the other impact domains affect humans in many ways, they focus on the Earth's biosphere as a whole. This group of impact categories is human-centric.
Toxic chemicals released to the air, water, and soil enter the human body through breathing, ingestion, and through the skin. Whether cancer-causing agents (carcinogens), substances that can cause birth defects (teratogens), or other pathogens, the net result is an increased likelihood of human sickness and other negative health effects.
Many organic causes of respiratory problems are covered by some of the general environmental impacts already covered (e.g., photochemical oxidation). Respiratory inorganics are particulate matter, often resulting from the burning of fossil fuels emitting sulphate and nitrate aerosols. This particulate matter causes breathing difficulties.
Ionizing radiation is what most people are thinking of when they talk about radiation exposure. It is radiation that has enough energy to ionize atoms or molecules. Exposure can damage living tissue, resulting in cancer, radiation sickness, mutation, and even death.
The impact categories described above represent most of the major ones that you are likely to come across, although occasionally with different names or classifications. While all may seem important, each one requires data collection and reporting, which may or may not be feasible given the time and intention of the sustainability assessment. There are trade-offs in the value of including a broad range versus just focusing on one or two, a difference that multiplies depending on how many stages of the lifecycle fall within the assessment's scope.
 Jolliet, O., Margni, M., Charles, R., Humbert, S., Payet, J., Rebitzer, G. and Rosenbaum, R., 2003. IMPACT 2002+: A New Life Cycle Impact Assessment Methodology. Int J LCA 8 (6), 324-330. Article
 Adapted from "Life Cycle Assessment: Principles and Practice," Scientific Applications International Corporation, EPA/600/R-06/060 (May 2006), pg. 49.
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