A Geobiosphere Baseline for LCA – Emergy Evaluations

52 A Geobiosphere Baseline for LCA – Emergy Evaluations Mark T. Brown and Sergio Ulgiati ABSTRACT The empower that is derived from solar energy, tidal momentum and geothermal energy drives the productive processes of the geobiosphere and is responsible for developing gradients of potential energy transformed into secondary energy sources (wind, chemical potentials of water, and waves) and tertiary sources (chemical and geopotential energy of river discharges and the available energy in breaking waves). In this paper we establish the geobiosphere emergy baseline based on earlier methods proposed by Odum, (2000) and refinements by Brown and Ulgiati (2010) based on accounting for a different interpretation of secondary and tertiary driving sources. Additionally, we suggest that defining spatial and temporal boundaries is critical to emergy evaluations. Spatial boundaries should be three dimensional and include a depth below the land surface in order to compute geothermal exergy input and height above the land surface to include adsorption of geostrophic winds. Specifying the temporal boundaries of an analysis helps to allocate driving emergy sources properly, especially related to landscape scale analyses. THE GEOBIOSPHERE EMERGY BASELINE (GEB) Baseline - A measurement, calculation, location, or standard of value used as a basis for comparison. Information that is used as a starting point by which to compare other information. A frame of reference. Baselines are important, if for no other reason than to provide a standard reference point from which we can view the universe. In the emergy accounting method we use the geobiosphere and the annual flux of energy driving it as the frame of reference for computing all Unit Emergy Values (UEVs). We could use a cosmic baseline and the big-bang as the starting point of energy embodiment, as some have suggested (Chen et al. 2010); however in doing so, the computations that result are a bit more uncertain and difficult, as we must keep track of more zeros. A second frame of reference used in the emergy methodology is the solar baseline from which the quality of different forms of energy is computed. One could use a different baseline, for instance Coal Equivalents1; however, in using Coal Equivalents, energies of lower quality have values that are less than one (a Joule of sunlight, for instance, would be something on the order of 0.000015 Joules of coal equivalent). So, the emergy method uses the geobiosphere as the spatial frame of reference and solar energy as the energetic baseline because of practical reasons that make calculations easier and numbers less uncertain. A frame of reference for time is also important. When evaluating a product or service of the geobiosphere system, there must be a beginning and an end. Since emergy is the amount of available energy required to produce something, the question often arises... “to compute the emergy required, how far back in the past does one go?” For instance, if one were evaluating the emergy required to 1 In fact, a baseline of Coal Equivalent Calories was used in the early 1980’s for a couple of years during the initial development of the emergy methodology (see Brown and Ulgiati, 2004) 481 produce a computer, where does one start, with the computer, with the inputs that lead to the invention of the vacuum-tube since it was the precursor to the transistor which lead to the silicon chip? Or should we include all the energy since the industrial revolution? Or should one start accumulating emergy at the beginning of Earth history (4.5 billion years ago), since it can be reasoned that anything that is produced today is the result of embodiment of all Earth’s energy and information since “the beginning”? Obviously any of these starting points are correct if they are utilized for all evaluations, since they only refer to a frame of reference; and just as obvious, it should be recognized that it makes no difference as long as the timeframe is consistently applied. In the emergy methodology, the timeframe is usually set by turnover time2 of the system being evaluated. In general, the temporal reference frame is related to the system of interest only and does not include all the evolutionary steps that may have gone before. In a way however, evaluations of human systems do include much system evolution since human labor and services are included and these human inputs are primarily information. The information that humans invest in a process as labor or services is the cumulative information embodied in the individual, which includes not only the information gained in his/her life-time, but the cumulative societal information that each individual carries. Regardless of what time frame is used in an emergy analysis, the description of the system should include sufficient detail that the time domain is explicitly understood. EMERGY FLOWS OF THE GEOBIOSPHERE The biosphere (Figure 1) is driven by renewable inputs of solar energy, tidal momentum, and geothermal heat (deep heat) each contributing to geologic, climatic, oceanic, and ecologic processes that are interconnected with flows of energy and materials. These three driving sources are referred to as the global tripartite and are the primary sources of renewable emergy driving geobiosphere processes. In Figure 1, the flows of available energy from air, land, and oceans interconnect these components, forming mutually reinforcing web. Through these interconnections the main components of the geobiosphere cycle material and energy and each component exchanges inputs from and outputs to each of the others. After millions of years of self-organization, the transformations of the driving energies by the atmosphere, ocean, and land are organized simultaneously to interact and contribute mutual reinforcements. This fact is the basis for calculating UEVs for all the products of the geobiosphere, whether materials, energies, or information3. In a recent paper (Brown and Ulgiati, 2010), the available energy of sunlight, tides and geothermal sources were reevaluated based on a method first used by Odum (2000). Since Odum’s evaluation in 2000, there has been considerable progress in measuring the solar constant and tidal momentum transferred to Earth yielding relatively precise estimates. However, the estimates of geothermal heat and the sources of that heat are still subject to relatively large uncertainty. In order to deal with this 2 sometimes called replacement time, or the amount of time required for replacement by flow-through of a system’s energy or material, and is calculated as the ratio of the system’s content of that substance to its flow-through rate. 3 It should be mentioned that Campbell et al (2005) have suggested more than one baseline is justified and proposed 9.26 E24 seJ/yr as an alternative to the baseline computed by Odum (2000). Also Campbell (2000) in an earlier analysis suggested two baselines 9.26 E24 seJ/yr and 10.58 E24 seJ/yr for short and long period processes respectively. Most recently Campbell, Bastianoni, and Lu (2010) argue that the 9.26 E24 baseline is the most appropriate because it assumes that only the sun and deep heat are responsible for generating geologic processes. 482 Figuure 1. Earth geobiosphere, a hierarchical web of components connected by flows of avvailable energy and materials that build potential energy and circulate materials Table 1. Emergy inputs to the geobiosphere calculated using exergy of main sources (Brown and Ulgiati, 2010). Note Inflow Solar Transformity Empower* (seJ/J) (E24 seJ/yr) 1 Solar energy absorbed 1 3.6 2 Crustal heat sources 20,300 3.3 ± 0.15 3 Tidal energy absorbed 72,400 8.3 ± 0.15 Total global empowere -- 15.2 ± 0.3 seJ/J = solar emjoules per joule * Median values from Monte Carlo simulation of the emergy equations Notes to Table 4-1 1. Transformity is 1.0 by definition; exergy flow: 3.59 E24 J/yr 2. Transformity is median value from emergy equation for crustal heat solved using equations 1 and 2; median value for exergy release by radioactivity and deep heat from the Monte Carlo simulation was 5.1 TW (1.63 E20 J/yr). The heat generated by crustal sources is not added here to avoid double counting. 3. Transformity is median value from Monte Carlo simulation of the emergy equation for geopotential of oceans. Energy flow 1.17 E20 J/yr (Munk and Wunsch, 19988) uncertainty, Brown and Ulgiati (2010) chose median values for the geothermal energy contributions out of a Monte Carlo simulation. The three main driving forces of sun, deep heat and gravitational potential provide a total emergy contribution to the geobiosphere (Table 1) of about 15.2 E24 seJ/yr (Brown and Ulgiati, 2010). Prior to that date, Odum et al. (2000) using slightly different solar, tidal and deep heat values calculated the global empower as 15.83 E24 seJ/yr. In 1996, in the book Environmental Accounting, Odum (1996) used a different procedure to compute a total emergy support to the geobiosphere of about 9.44 E24 seJ/yr. Each time there is a change in the reference baseline the UEVs which directly and indirectly were derived from the value of global annual empower must also change. The difference between the 483 current geobiosphere baseline computed by Brown and Ulgiati (2010) and that computed by Odum et al. (2000) is about 4%, thus it is not necessary to recalculate or adjust prior evaluations or transformities derived from the 2000 base since this is well within the uncertainty of the calculated base empower. UEVs calculated prior to 2000 (based on the 9.44 E24 seJ/yr baseline) should be multiplied by 1.61 (the ratio of 15.2/9.44). TRANSFORMITIES OF SECONDARY GLOBAL AVAILABLE ENERGY FLOWS Sunlight, tidal momentum, and geothermal heat power the geobiosphere; their energy flows are transformed into secondary global flows that include wind, rainfall, and ocean currents.

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