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A Geobiosphere Baseline for LCA – Emergy Evaluations

Mark T. Brown and Sergio Ulgiati

ABSTRACT

The empower that is derived from , tidal momentum and drives the productive processes of the geobiosphere and is responsible for developing gradients of 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 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 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 (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, 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.

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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. 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 , 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. Table 2 summarizes these secondary flows, their available energy, and their transformities. The hierarchical web of energy flows of the geobiosphere illustrated in Figure 2 shows the main driving energies and the pathways of available energy flows linking the continents, oceans and atmosphere. The diagram makes visible the interconnected nature of the geobiosphere which results in the transformation of driving energies into secondary energy flows, with the products of all three driving energies acting collectively to build structure and increase power flows. In Table 2 the baseline emergy (sum of sunlight, tidal momentum, and geothermal heat) is used to calculate transformities of the secondary flows. Transformities are computed by dividing the total global emergy (15.2 E24 seJ/yr) by the flow of available energy for each secondary source. Secondary sources are ordered based on increasing transformity. Notes to the table provide details of the calculations for each secondary energy.

Wind Energy

The global average 10 meter height wind speed over the ocean from measurements is 6.64 m/s...; that over land is 3.28 m/s....(Archer and Jacobsen, 2005). Taking the 10 meter height as the surface wind speed, Reiter (1969) estimated that the speed of geostrophic winds is 1.67 times higher than for surface winds, yielding a ratio of surface wind speed to geostrophic wind speed of 0.60. Hasse & Wagner (1971) estimated the average ratio of surface winds to geostrophic winds equal to 0.56 using regression analysis of 438 observations. We use the Hasse & Wagner value, since it is based on empirical evidence, to compute the wind energy adsorbed by surface processes. Wind energy adsorbed by surface processes is the difference between surface wind and geostrophic wind. The energy in wind is given by:

3 Energy  (Density)(Drag _ coefficient)(Velocity )(Area)(Time) (1)

Where: Density of air = 1.23kg/m-3 at 1 atmosphere and 15 degrees C Drag coefficient over ocean =0.0001; over land = 0.03 (Palutikof, et al. 1984) Velocity adsorbed = speedgeostrophic wind – speedsurface wind= (speedsurface wind/0.58) – speedsurface wind Area of Earth Surface = 5.1E8 km2, Ocean = 3.62E8 km2, Land = 1.48 E8 km2 Time = 3.15 E7 sec/yr.

Energy = (1.23 kg/m3)(1.0 E-4)(6.64/0.56 – 6.64)3(3.62 E14 m2)(3.15 E7 sec/yr) + (1.23 kg/m3)(0.03)(3.28/0.56-3.28)3(1.48 E14 m2)(3.15 E7 sec/yr) = 3.14 E21 J/yr

UEVwind = 15.2 E24 seJ/yr / 3.14 E21 J/yr = 4.8 E3 seJ/J

The UEV of surface wind is larger than the value computed by Odum (2000), 2473 seJ/J.

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Table 2. Solar transformities of secondary global available energy flows (Brown and Ulgiati, 2010). Global Solar Energy Emergy Flux Solar Transformity Noote Item (seJ/yr) (E20 J/yr) (seJ/J) 1 Surface wind 1.52E+25 96.3 4,800 2 Chemical potential energy of rain 1.52E+25 23.9 6,600 3 Ocean currents 1.52E+25 1.6 96,203 (See text for calculations.)

Figuure 2. Secondary emergy flows of the geobiosphere (rraain, wind, and ocean currents driven by tripartite flows from sunlight, tidal energy and deep heat. Cumulative stored heat in the geobiosphere is heat that has a gradient with the average environmental temperature and the heat sink represents energy that is dispersed and has no gradient with the environment and therefore is not capable of doing work.

Rain (Chemical Potential)

The global UEV for chemical potential of rain was re-evaluated by Brown and Ulgiati (2010, in draft) following the methods of Odum (2000). Odum (2000) assumed that the rainfall over land was a co-product with rainfall over the oceans, thus the numerator used to compute the UEV of terrestrial rainfall was the total GEB. Brown and Ulgiati (2010, in draft) re-examined the method and suggested that terrestrial rainfall should not be a co-product with marine rain, but instead a split. Thus the UEV of rain was computed by dividing the GEB by total rainfall, rather than just the terrestrial rain as follows: Rain - global annual average precipitation = 4.86 E20 g/yr (Adlerr et al. 2003) Assume average dissolved solids in rain = 10 ppm Earth surface = 5.1 E8 kmk 2 Gas Constant = 8.3143 J mol-1 K°-1 Temperature = 287.25° K (average global temperature during the 20th century of 14.1°C (http://www.ncdc.noaa.gov/sotc/global/2013/10) + Absolute temp 273.15° K

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Gibbs free energy of rain as follows: J 8.3143 / K *287.25K 6 RT C 10  Sppm G  ln 2  mole *ln (2) g 6 W C1 18 10  So ppm mole J 8.3143 / K *287.25K 6 10 10ppm  mole *ln  4.72J / g g 6 18 10 35000ppm mole

2 2 2 Energyrain = 2.6 mm/day * 0.001m/mm*365 da * 5.1 E8 km * 1 E6 m /km * 1.0 E6 g/m3*4.72 J/g = 22.8 E20 J

UEVrain = 15.2 E24 seJ/yr / 22.8 E20 J = 6.60 E3 seJ/J.

Ocean Current Energy

The USDI (2006) estimated total global available energy in ocean currents as 5 TW, and energy is as follows:

Energy = 5.0 E12 W/yr*3.15 E7 sec/yr = 1.58 E20 J/yr

The computed transformity of ocean currents is as follows:

UEVcurrents = 15.2E24 seJ/yr / 1.58 E20 J = 96,200 E3 seJ/J.

TRANSFORMITIES OF TERTIARY GLOBAL AVAILABLE ENERGY FLOWS

The global available energy of what we term tertiary flows are driven indirectly by the primary flows, but directly by splits of the biosphere’s available energy. The tertiary flows include the chemical and geopotential energy of river discharges and the available energy in breaking wave on shorelines of continents. Table 3 summarizes the average annual available energy in river discharges and breaking waves, the driving emergy and computed global average transformities.

Geopotential Energy in Rivers

The continental runoff, also known as river geopotential and called rain geopotential by Odum (2000) is computed from the average annual global river discharge (3.73E4 km3) from Dai et al. (2009) and average continental elevation, 797 m (Eakins and Sharman, 2013). The geopotential energy is given by:

Energy  (Mass)(Gravity)(Height) (3)

Energy = 3.73E4 km3*1.0E12 kg/km3*9.8 m/s2*797 m = 2.91E20 J/yr

Emergy of continental rainfall is 3.56E24 seJ/yr. (see above), thus the average UEV of rivers geopotential is:

UEVriver geopot= 3.56E24 seJ/yr/ 2.91 E20 J = 12,200 seJ/J

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Table 3. Solar transformities of tertiary global available energy flows. Solar Emergy Energy Flux Solar Transformity Note Item (seJ/yr) (E20 J/yr) (seJ/J) 1 Geopotential energy of river flow 3.60E+24 3.3 10,909 2 Chemical potential energy of river flow 3.60E+24 2.0 18,000 3 Waves absorbed on shore 1.06E+25 4.8 22,167 (See text for calculations.)

Chemical Potential Energy of River Discharge

River discharges are 3.73 E4 km3. We assume an average dissolved solids concentration of 500 ppm, therefore the Gibbs free energy =4.66 J/g, and the total available energy in river discharges is as follows:

Energy = (Mass)(Gibbs energy) (4) = 3.73 E4 km3* 1e15 g/km3*4.66 J/g = 1.74 E20 J/yr.

Emergy of continental rainfall is 3.56 E24 seJ/yr (see above), thus the UEV of rivers chemical potential is:

UEVriver chem pot= 3.56E24 seJ/yr / 1.74 E20 J = 20,500 seJ/J

Wave Energy

The global UEV for breaking waves was reevaluated by Brown and Ulgiati (2010, in draft) as follows:

Annual global gross theoretical wave power = 3.7 E12 W (Gunner et al. 2010 using the WorldWaves data set of (Barstow et al., 2008).

Energy = 3.7 E12 W/yr *3.15 E7 sec/yr = 1.17 E20 J/yr (5)

Assume driving emergy = Wind energy over oceans (see above)* Wind UEV

Emergy= [(1.23 kg/m3)(0.03)(3.28/0.58-3.28)(1.48 E14 m2)(3.15 E7 sec/yr)]*5.4 E3 = 2.21 E+24 seJ/yr

UEVwaves = 2.21 E24seJ/yr /1.17 E20 J/yr = 18,900 seJ/J

CALCULATING EMERGY INPUTS TO LOCAL SYSTEMS

The process of evaluating the driving emergy inputs to a smaller portion of the geobiosphere, a local portion of the earth’s surface, begins with a conceptual model of the system, which is translated into a systems diagram such as that in Figure 3. The diagram is of an average square kilometer of the Earths surface area that includes both land and the submerged portion of the continental shelf. We use an “average” of the global landscape to illustrate how to calculate input energies, thus we have taken the land area, coastal length and area of continental shelf of globe and scaled them so that the km2 represents the distributions of these components on earth. For the purposes of this exercise, we are not including humans and the nonrenewable energies that drive human dominated processes.

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Figuure 3. Energy systems diagram of a landscape system useed to evaluate the renewable emergy input in Table 4.

The systems diagram shows the flows of driving energies interacting with the marine and terrestrial driving the cycles of materials and energy, generating storages of higher quality biomass and living component, some exiting the system as unusable energy that no longer has the ability to do work (degraded exergy), and some exported to the larger environment in which it is embedded. The upper and lower system boundaries for this analysis are 1500 meters in elevation to 1000 meters depth in the earth’s crust. The upper system boundary of 1500 meters was chosen to include the atmospheric boundary layer for the purposes of computing the wind exxergy absorbed, since, on the average, the boundary layer is between 1 and 2 km in height. The lower system boundary was chosen to include sufficient geothermal exergy for some crystal geologic activity.. Calculation of geothermal exergy relies on computing a Carnot efficiency for the energy in the theermal gradient between the temperature of the heat source and the temperature of the reference environment. In this case the reference temperature (average temperature at earth’s surface) is taken as 287 K (i.e. 273 K plus 14°C average surface temperature of the Earth) and the temperature at 1000 meters is 317 K (temperature increases by 3oC per 100 meters) thus the average temperature of the crust under the one-hectare system boundary is 303 K and the Carnot efficiency is 1- (287/317) = 9.5% Table 4 summarizes the emergy evaluation, where thhe flows of energy are first converted to exergy and then multiplied by their transformities to yield emergy. Footnotes to the table explain the assumptions and computations for each flow.

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Table 4. Emergy evaluation of renewable inputs to 1 kilometer of the Earth's surface. Note Item Raw Units Transformity Solar Emergy (seJ/unit) (E15 seJ) RENEWABLE RESOURCES: 1 Sunlight 7.09E+15 J 1 7.1 2 Wind, kinetic energy 1.51E+12 J 5,400 8.2 3 Rain, chemical potential 2.78E+12 J 6,600 18.3 4 Runoff, geopotential 6.73E+10 J 12,200 0.8 5 Earth Cycle, heat flow 1.90E+11 J 20,300 3.9 6 Runoff, chemical potential 1.13E+12 J 20,500 23.2 7 Waves, kinetic energy 5.34E+10 J 18,900 1.0 8 , kinetic energy 3.67E+10 J 72,400 2.7

Footnotes to Table 4 1 SOLAR ENERGY: Area = 1.00E+06m2 (sum of land and shelf area) Insolation = 2.60E+02 Kcal/cm2/yr Albedo = 30.00 (% of insolation) Carnot Efficiency = 0.93 Energy(J) = (area incl shelf)*(avg insolation)*(1-albedo)*(4186 J/Kcal)*(Carnot efficiency) = (____m2)(____Cal/cm2/y)(E+04cm2/m2) (1-0.30)(4186J/kcal) = 7.09E+15 J/yr Transformity = 1 seJ/J

2 WIND ENERGY: Area = 1.00E+06m2 Density of Air = 1.30 kg/m3 Avg. annual wind velocity = 5.00 m/s (Archer and Jacobsen, 2005) Geostrophic wind = 8.33 m/s - Observed winds are about 0.6 of geostrophic wind (Reiter, 1969) Wind Velocity absorbed= 3.33 m/s Drag Coeff. = 1.00E-03 (Kraus, 1972) Energy (J) = (area)(air density)(drag coefficient)(wind velocity absorbed^3) = (_____m2)(1.3 kg/m3)(1.00 E-3)(______mps)(3.14 E7 s/yr) Energy(J) = 1.51E+12J/yr Transformity = 5,400 seJ/J

3 RAIN, CHEMICAL POTENTIAL ENERGY: Land Area = 8.50E+05 m2 Shelf Area = 1.50E+05 m2 Rain (land) = 0.77 m/yr (from Appendix A) Transpiration rate= 65 % (from Table X) Rain (shelf) = 0.92 m/yr Rain on oceans 20% > than land (Adler et al., 2003) Energy (J)= (land area)(rainfall)(% transpired)(Gibbs energy of rain) + (Shelf area)(rainfall)(Gibbs energy of rain) = (____m2)(____m)(___%)(1000kg/m3)(4.72E+03J/kg) + (____m2)(____m)(1000kg/m3)(4.72E+03J/kg) = 2.78E+12 J/yr Transformity = 6600seJ/J

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4 RUNOFF, GEOPOTENTIAL ENERGY: Land Area = 8.50E+05 m2 Rainfall = 0.77 m Avg. Elev. = 30.00 m (estimate) Runoff rate = 35 % Energy(J) = (land area)(% runoff)(rainfall)(avg. elevation)(gravity) = (____m2)(____m)(1000kg/m3)(____m)(9.8m/s2) = 6.73E+10 J/yr Transformity = 12,200 seJ/J

5 EARTH CYCLE Area = 1.00E+06 m2 Heat flow = 2.00E+06 J/m2/yr (International Heat Flow Database, 2010) Carnot efficiency = 9.5% (1- 287 K/ 317 K Energy (J) = (area)(heat flow)(Carnot efficiency) = 1.9E+11 Transformity = 20,300 seJ/J

6 RUNOFF, CHEMICAL POTENTIAL: Land Area = 8.50E+05 m2 Rainfall = 0.77 m Runoff rate = 35 % Energy (J)= (land area)(rainfall)(% runoff)(Gibbs energy of runoff) = (____m2)(____m)(___%)(1000kg/m3)(4.66E+03J/kg) = 1.13E+12 J/yr Transformity = 20,500 seJ/J

7 WAVE ENERGY: Shore length = 1.00E+00 m Wave height = 5.00E-01m (estimate) Depth = 3.00E+00m (estimate) Wave velocity = 5.42E+00 m/sec (velocity = sq.root of gravity*shoaling depth) Energy(J) = (shore length)(1/8)(density)(gravity)(wave height2)(velocity)(3.14 E7 s/yr) = (___m)(1/8)(1.025 E03kg/m3)(9.8 m/sec2)(___m)2(___m/sec)(3.14 E7 s/yr) = 5.34E+10J/yr Transformity = 18,900 seJ/J

8 TIDAL ENERGY: Area = 1.00E+04 m2 Avg Tide Range = 1.00 m (estimate) Density = 1.03E+03 kg/m3 Tides/year = 7.30E+02 (estimate - 2 tides/day in 365 days) Energy(J) = (shelf)(0.5)(tides/y)(mean tidal range)2(density of seawater)(gravity) = (____m2)(0.5)(____/yr)(____m)2(_____kg/m3)(9.8 m/s2) = 3.67E+10 J/yr Transformity = 72,400 seJ/J

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SUMMARY AND CONCLUDING REMARKS

Transformities computed in this manner, using global averages, are average values. It should be understood that there is no single unit emergy value for any given product, since no two processes are alike. This also holds for the processes of the biosphere. For instance there are many transformities for rain depending on location and even time of year. Precipitation varies with altitude, is affected by mountains, and depends on the weather systems in complex ways. The rainfall in any particular location may have a higher or lower transformity depending on the source area and intensity of the solar energy driving the cycles that produce it. Calculation of transformities on a site specific basis for such things as rainfall is not an easy undertaking because of the uncertainties inherent in estimating the input variables. Therefore, to simplify evaluations, average global transformities can be used if the system under study represents more or less average conditions. Care should be taken, however when using average transformities if environmental conditions suggest that the reference state for the system is significantly different from average global conditions.

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