Dimensional and dimensionless environmental metrics
As we do when we discuss the fuel efficiency of a car, it is useful to express environmental performance indices, or “environmental metrics”, as ratios of one quantity, e.g., kilograms of emissions of NOx or CO2, to another, e.g. per kwh produced. This particular measure has the dimensions of mass/energy (kg/kWh) and is called “dimensional”. In contrast the metric “kg copper in copper product A per kg of copper mined for manufacture of product A” has the dimensions of mass/mass and, therefore, is “dimensionless”. In your term paper, try to express, as much as possible, your results in the form of such dimensional or dimensionless ratios; you will be contributing to the nurturing of IE.
Figure 1. “Cradle to Grave” Assessment of Environmental Impacts
The “master environmental equation”
As discussed in class, because of the high fluidity of atmospheric air and the incessant wind motion over the surface of the Earth (e.g. of southwesterly winds over North America), long-lived gas species, such as carbon dioxide (life time in atmosphere of about 5 years), become evenly distributed over the entire troposphere, no matter where they were generated. The enormous emission of anthropogenic carbon to the atmosphere (presently 6.5 billion tons per year or about 6.5% of total pre-industrial emissions of carbon) has raised the specter of global warming and has brought all nations to the negotiating table (e.g. Rio and Kyoto conferences). So let us start by establishing some measure of the contribution of each nation to global warming. This can be done by means of the “master environmental equation” that consists of three terms:
population
material standard of living (Gross Domestic Product or GDP, in $) per person
environmental impact per unit of material standard of living (reflects level of technology used in industrial activities
With respect to global warming, the last term can be expressed as “tons of carbon dioxide equivalent, CO2,equ per $ of GDP” where “CO2,equ“ sums up all carbon dioxide and all other “greenhouse gases (GHG)” that have an equivalent effect (e.g. one ton of methane, CH4, emissions are equivalent to about 21 tons of CO2). Accordingly, the master environmental equation is expressed in algebraic form as follows:
National environmental impact =
= (national population)*(GDP/capita)*(environmental impact/GDP).
The above equation shows that the three contributing factors are the size of population (e.g., China), very high material standard of living (e.g. the U.S.) and inefficient technology for fuel combustion and gas emission control (e.g. in developing nations). The “population” term can be reduced by public awareness or government action (China). The GDP/capita term represents the material standard of living. The third term is indicative of the technology used to produce materials and energy and to control emissions. Of course, this is the main subject of this course. It should be noted that the at the present time the Gross Domestic Product includes all products and services paid for in local currency- it does not include environmental costs of a particular activity.
Proposal: The “incremental master environmental equation”
Inspection of Figure 2 (Growth in Global Population by Geographic Area) shows a good reason for developing a second form of the master environmental equation: The population of developing nations in Asia and Africa has exploded since the beginning of what we may call the “2nd industrial revolution” in the 1950’s. If this trend continues, the globe will face many severe problems (e.g. food, water and material shortages) besides global warming. Therefore, it is necessary for the developed nations to curb their use of material and energy resources and also for the developing ones to curb population growth; or for both to be prepared to pay the consequences of irresponsible behavior. To “level the playing field”, it may be useful to establish an “incremental master environmental equation” that uses the year 1950 as a time reference point and compute the change in the three contributing terms since 1950 and for projections into the future:
t (National environmental impact) =
= t oo[(national population)* (GDP/capita)* (environmental impact/GDP)].
where the increment t represents the product of the three terms at time t minus the same product in 1950. The first home exercise of the IE class will involve the calculation of the master equation and the incremental Master equation for five representative nations.
National material flows
One of the most useful metrics is the annual use of various materials per person and it is readily obtained from published census and production records that all nations, and states and provinces within a nation, keep. For example, Table 1 shows the U.S 1991 material inputs to all industrial activities. It can be seen that the largest consumption is of fossil fuels, followed by construction minerals and agricultural products. The 1991 total material flow amounted to 20.25 tons per capita.
