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

Thermhaline current “global conveyor belt”

Color key is NOT temperature!

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

Radioactive decay chains

Radioactive decay of heavier nucleiFrom http://commons.wikimedia.org

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

Source: http://en.wikipedia.org/wiki/Solar_radiation

= nanometer = 10-9 meter

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%

Source: Nasa ERBE

BB 5800 K

BB 300 K

Global radiation flows

Source: Smil, General Energetics

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

Global water cycle flows

Source: Smil, EnergiesUnits: W/m2 (I think)

Global Wind Flows

Source: Smil, Energies

Wind and extractable energy

Source: Smil, Energies

Pow

er (

Wat

ts)

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

Troph flow chart

Carbon from CO2?

NoYes

Autotrophs Heterotrophs

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

Atmospheric composition

Source: Smil, Energies

Photosynthesis

Absorption of terrestrial radiation

Source: Smil, EnergiesPeak of earthradiation at 300K

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?

Source: J. Siirola, GRC 2006

CO2

Carbondioxide

CH4

Methane

Carbon oxidation states, cont.

And end here

Decreasing energy availability

Plants starthere

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

The Trophic System of different Ecosystems

Courtesy of Karlheinz Erb

The Trophic Net

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

NPP – Correlation with Climate

Courtesy of Karlheinz Erb

ANPP of the World Ecosystems

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

Courtesy of Karlheinz Erb

Courtesy of Karlheinz Erb

NPP and the Carbon Cycle

Courtesy of Karlheinz Erb

The Global Carbon Cycle

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

BMR of humans

(Harris & Benedict, 1919)

kcal

/ d

ay

50 W

80 W

BMR by organ

Source: Durnin 1981 http://www.fao.org/DOCREP/MEETING/004/M2845E/M2845E00.HTM

Human food energy requirements

Smil, Energies

Human BMR vs. gender, age

from Mitchell, 1962

Energy costs of motion (food capture)

Source: Smil, General energetics

Energy cost of human activities

Source: Smil, Energies

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