energy on planet earth sources of energy on earth? surface 1. solar radiation 2. extra solar...
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Energy on planet earth
Sources of energy on earth? Surface
1. Solar radiation
2. Extra solar radiation (very very small)
Very well understood
Core 1. Radioactive decay of earth’s
core elements (up to 90%)
2. Core cooling (left over gravity) (5-10%)
3. Gravity (friction between elements of different density) (5%)
4. Latent heat from expansion of cooling materials (small)
Not so well understood!Source: www.physorg.com/news62952904.html
2 more obscure sources?
1. Earth’s rotation Coriolis effect: trade winds and ocean currents
2. Moon Tides
Radioactive heating of earth’s core
Radioactivity involves the decay of unstable nuclei of atoms In the earth’s core, these are mainly Uranium,
Thorium and Potassium Potassium is also the main source of human
radioactive exposure
Earth core total heat generation estimated30 - 44 TW (1 TeraWatt = 1012 Watts) Radioactive component measured
in 2005 through antineutrino detection by KamLAND (Japan)24 TW
10 TW = 1990 global fossil fuel use
Sources: http://athene.as.arizona.edu/~lclose/teaching/a202/NewScientist, July 27 2005
Some solar numbers
Sun mass = 2 x 1030 kg = 333 thousand earth masses
Sun radius = 7 x 108 meters= 100 x earth’s radius
Sun-Earth distance = 150 x 109 metersroughly 2000 x earth’s radius
Density = 1.4 tonnes / cubic meter = 25% as dense as the earth
Surface temperature = 5’778 KelvinEarth surface temp = 287 Kelvin (14 Celsius)
Power radiated (Luminosity) = 3.85×1026 W
Solar radiation on earth
Total power radiated =3.85×1026 W
Power density at earth’s orbit = 1’367 W/m2 = SOLAR CONSTANT Actually not a constant, increased by 30% over 3 billion years
of life on earth! Stability of climate during this time is one basis of Gaia
hypothesis.
Average power density at earth upper atmosphere = 342 W/m2
Because of earth is rotating sphere, divide solar constant by 4. Reaching the ground: 240 W/m2
Total 122 PW = 122 x 1015 Watts Compared to 30-44 TW from earth core heating
Spectral qualities of solar radiation
Light (or radiation) is characterized by wavelength/frequency (colour) and intensity.
Spectrum is the shape of the intensity vs. wavelength Wavelength and frequency are directly related to each other:
wavelength = (speed of light) / frequencyspeed of light = 299’792’458 meters / secondHigher frequency => higher energyHigher wavelength => lower energy
“Black body” radiation means the relation between the wavelength and the intensity are determined by the temperature of the radiating object alone
All objects at the same temperature have the same black body spectrum.
Solar spectrum is Black body radiation at 5800 Kelvin
Perfect black body
The most perfect black body radiation ever measured:The cosmic microwave background radiation at 2.725 Kelvin
= 1 / wavelength
Energy distribution of solar spectrum
Wavelength (nanometer = 10-9 meter)
Percentage of total energy
< 300 X-rays and gamma rays
1.2%
300-400Ultra-Violet
7.8%
400-700Visible
38%
700-1500Infrared
38.8%
> 1500Microwaves, Radio waves
12.4%
Uses for all this radiation
300 Kelvin planet: water is liquid!Visible light: energy which can be used
by “autotrophs”
Solar radiation and core heat:Secondary phenomena & energy sources
Wind, tornadoes, hurricanes, jet streams (in part due to earth’s rotation)
Waves, ocean currents (in part due to earth’s rotation)
Tides (due to moon) Earthquakes, volcanic eruptions, tsunamis Global water cycle (rain, snow, rivers, glaciers,
erosion) Requires 40 PW (third of solar radiation)
Geothermal energy
Thoughts on global energy processes
Small number of primary sources (sun, moon, rotation, core heat)
Energy is transferred and reused in many ways once it reaches the lithosphere-atmosphereMovement of masses (tectonic plates, water, ice,
crust, air)Transfer of temperatures (water, absorption and re-
radiation of light, volcanic eruptions and geothermal processes)
Sorting of matter based on density.
Life on earth is based on taking advantage these energy various energy flows.
Some biology vocabulary
Biomass: mass or energy of organisms (living or ex-living) per unit area of land or unit volume of water Units J/m2 or tonne/hectare
Phytomass: plant biomass (stock) Autotroph: organism which does not feed on other organisms, but
relies on chemical, thermal or radiation energy in its environment: producers in the food chain Plants, some bacteria
Heterotroph: organism which feeds on organic matter created by other organisms: consumer in the food chain Everyone else
Primary production: rate of phytomass production Units J/m2/day or tonne/hectare/year
Secondary production: rate of non-plant biomass production
Life on earth
When? 3.5 billion years ago (Archean era)Sun & earth 5 billion years old … and another 5
billion to go.
Who? Prokaryotes Archaea: autotrophs Lots of CO2 in atmosphere, sequestered to
CaCO3 (limestone) Inorganic geochemical processes?Early life forms?
Missing in atmosphere? O2
Photosynthesis: primary production
Plant input: Carbon dioxide + water + sunlightCO2 + H2O + light
Plant output: Carbohydrate + oxygen + waterCH2O… + O2 + H2O
Carbon is “fixed” in plant, providing food for heterotrophs Oxygen is released into
atmosphere
Why do plants do it?
Efficiency of photosynthesis
Efficiency of photosynthesis = stored chemical energy / incident sunlight
Factors influencing efficiency (1) Theoretical constraints
Only 43% of incident sunlight is Photosynthetically Active Radiation (PAR), wavelengths 400-700 nm
Chemical reaction efficiency of carbon assimilation is 90% Quantum probability requirements of light per molecule 30% Total theoretical efficiency = 12%
(2) Practical constraints Light reflected from & transmitted through leaf surface 10-25% Angle of leaf to sunlight is often not 90%, often not direct sunlight Energy costs of respiration (40%), rapid rates of photosynthesis Plant metabolic processes (maintenance, growth, reproduction) Only get 50% - 2 % of best theoretical performance
Total photosynthetic efficiency is 6%, most often lower
Limiting factors of photosynthesis
Water availabilityC3 and C4 photosynthesisC4 in warmer, dryer climates
Nutrient availabilityManaged ecosystems (agriculture) are
more productive.
Primary production
“Numerous intricacies of photosynthetic energetics remain unknown but certainly one of the most surprising weaknesses in our knowledge of life is our patchy understanding of phytomass stores and productivities. Our lack of satisfactory appraisal of photosynthesis on planetary and ecosystemic scales is more troubling than remaining gaps in our biochemical understanding.”
Vaclav Smil, General Energetics: Energy in the Biosphere and Civilization, 1991
Accounting for primary production
Gross primary production GPP: total fixation of carbon by autotrophs (primary producers)
Autotrophic respiration RA: lost energyHeterotrophic respiration RHTotal ecosystem respiration RE = RA + RH
Net Primary Production NPP: rate of production of new biomassNPP = GPP - RANet Ecosystem Productivity NEP = GPP – RENEP > 0 : Ecosystem is carbon sinkNEP < 0 : Ecosystem is carbon emitter
Trophic Model - Odum
NU
S
G
E
R
I A P
B
I = Input, ingested energy; NU = not used; A = assimilated energy; P = Production; R = Respiration; B = Biomass; G = Growth;S = Stored Energy; E = Excreted Energy
Courtesy of Karlheinz Erb
Energy Flow through Ecosystems
Atmos. CO 2 Pool
NPP
GPP
Photo- synthetc Biomass
Non-Photo- synthetic Biomass
Waste
Ab
ove
gro
und
Food
und
er
-
Leaf Production
Root, Branch, Seedprod.
Biomass ('state')
Net Primary Production ('process')
Entire Standing Crop
Courtesy of Karlheinz Erb
Ecological Parameters and Succession
0
2
4
6
8
10
12
0 10 20 30 40 50 60 70 80 90
age
Sta
nd
ing
Cro
p [
kg
C/m
²]N
PP
[k
g/m
²a]
0
1
2
3
4
5
6
Tu
rno
ver
[a-1
]
SC NPP µ [a-1]
Courtesy of Karlheinz Erb
NPP - Methods of Assessment
short term harvest technique - harvest an area (quadrats) at short term intervals to get NPP:
PN = B + D + C
where D = death, C = consumption and
B = Bt – Bt-1
Courtesy of Karlheinz Erb
Human Appropriation of Net Primary Production - Components
NPP0: NPP of the potential vegetation (i.e. absence of human interference)
NPPact: NPP of the actual vegetation
NPPh: Harvest of NPP
NPPt: NPP remaining in ecosystem after harvest
NPPt = NPPact - NPPh
HANPP = NPP0 – NPPt; NPPt/NPP0 [%]
HANPP = NPP0 – NPPact + NPPh
Courtesy of Karlheinz Erb
Human Appropriation of Net Primary Production
Aboveground N P P poten tial vegetation
1404 PJ/yr(100% )
200
400
1.400
1.200
1.000
800
600
[PJ/yr]
Aboveground NPP actual vegetation
1201 PJ/yr(86% )
Harvest512 PJ/yr
(36% )
NPP rem aining in ecosystem s
689 PJ/yr(49% )
Appropriationof NPP
(715 PJ/yr
(51% )
HANPP)
Courtesy of Karlheinz Erb
Heterotrophs
Heterotrophs eat, breathe, excrete and emit energyFood: ingested, then absorbed or excretedEnergy costs for basal & active metabolismBasal functions: temperature maintenance,
organ functionActivity needed to capture food.
Basal metabolic rate: Kleibner’s w3/4 law
Source: Smil, General energetics
Geometric considerations can explain the ¾:diameter of limbs goes as mass3/8 Power output of muscles goes as diameter2 Power goes as mass3/4
70 kg
Walking-Biking-Driving (part 2)
Assume 1/3 loss
3MJ fossil/MJ veg
1/2 meat1/2 veg
6MJ fossil/MJ meat
Conclusion: if you are an average American (or Swiss) meat-eater,it may be more efficient to drive a Smart than to walk ...
Energy cost of motorized food gathering
USA Person 70 kg, 1 km distance
Walking Biking Sitting
(1 minute)
AverageCar
(gasoline)
Smart Car(diesel)
Speed (km/h) 5 20 60 60 60
Person Energy used (MJ/km)
0.2 0.1 0.012
Car Gasoline or Diesel (litre/100km)
9 4.2
Car Gasoline Equivalent (litre/100km)
9 5.4
VEGETARIANPlant-based energy
(MJ/km)0.3 0.1 0.02
VEGETARIANFossil Energy
(MJ/km)0.8 0.3 0.05
VEGETARIANGasoline Equivalent
(litre/100km)2.0 0.6 9.1 5.5
CARNIVOROUS
Plant-based energy (MJ/km)
1.5 0.5 0.09
CARNIVOROUS
Fossil Energy (MJ/km)
1.6 0.5 0.09
CARNIVOROUS
Gasoline Equivalent (litre/100 km)
4.1 1.3 9.3 5.6
Assume1/3 loss
6 MJ fossil/ MJ meat
3 MJ fossil/ MJ veg.
½ veg½ meat
25% loss crude to gasoline
USA Person 70 kg, 1 km distance
Walking Biking Sitting
(1 minute)
AverageCar
(gasoline)
Smart Car(diesel)
Speed (km/h) 5 20 60 60 60
Person Energy used (MJ/km)
0.2 0.1 0.012
Car Gasoline or Diesel (litre/100km)
9 4.2
Car Gasoline Equivalent (litre/100km)
9 5.4
VEGETARIANPlant-based energy
(MJ/km)0.3 0.1 0.02
VEGETARIAN Fossil Energy (MJ/km) 0.8 0.3 0.05
VEGETARIANGasoline Equivalent
(litre/100km)2.0 0.6 9.1 5.5
CARNIVOROUSPlant-based energy
(MJ/km)1.5 0.5 0.09
CARNIVOROUS Fossil Energy (MJ/km) 1.6 0.5 0.09
CARNIVOROUSGasoline Equivalent
(litre/100 km)4.1 1.3 9.3 5.6
Assume1/3 loss
6 MJ fossil/ MJ meat
3 MJ fossil/ MJ veg.
½ veg½ meat
25% loss crude to gasoline