1. Timescales Geological time (big changes globally)
Glacial-interglacial cycles (really recent time) – associated with shifting land masses and effects on ocean circulation
Human time (anthropocene) – relationship to geological forces
Rates of change
Timescales of movement of material and energy
Evolution versus extirpation versus extinction
Human-induced rates of change versus rates of natural self-regulation

2. The Earth’s Energy Balance
A budgeting exercise

3. Over Time Origin of earth (4.6 bybp) Hadean & Archaen (4.6 – 2.5 bybp)
Dating of extra-terrestrial material
Hadean & Archaen (4.6 – 2.5 bybp)
unidirectional change in organization of material/planetary evolution; driven by energy from radioactive decay
Proterozoic & Phanerozoic (2.5 bybp to present)
Solar energy more important/recycling of materials

4. Major points
How do the various components of earth system move energy and matter on the earth’s surface?
Over long time scales the planet must be in steady state (input = output)
In the present system, energy balance at the earth’s surface is driven by solar radiation

6. Basic physics
Electromagnetic (EM) radiation if generally propagated as a wave
But EM can often behave more like a particle - photon

7. Waves defined by their speed (c), wavelength l, and frequency n
Frequency and wavelength are inversely related
c = ln
(cm/cycle or cm)
n = c/l
Wave number (n) = 1/l
(cycles/cm or cm-1)
Fig. 3-2

8. E = hn = hc/l Electromagnetic spectrum
High energy/high frequency/low l
Low energy/low frequency/high l
E = hn = hc/l
At times, EM radiation behaves more like a particle - photon
Fig. 3-3

9. EM
High energy photons (low l/high frequency) – e.g., UV – can break molecular bonds and initiate chemical reactions
Low energy photons (high l/low frequency) interact with molecules affecting their rotation of vibration

10. Flux
How energy (or any material) passes through a unit surface area per unit time
Can think of energy as a particle
Units: some mass per unit area per unit time
mg/m2/hr (= mg m-2 h-1)
mmol quanta/ m2/hr

11. Which passes through a larger unit area?
Which has the higher flux?

12. Think about how that affects energy
flux with latitude on earth.

13. Back to energy
Energy is expressed as Joules (J) – measures heat, electricity and mechanical work
1 J = calories
1 J = ×10−7 kilowatt hour
Power (the rate at which work is done or energy is moved) is expressed in Watts (W)
1 W = 1 J/second
W/m2 then is a unit of energy flux
=J/m2/s
Energy flux is important for global climate
Polar regions cooler due to lower energy flux (mass per unit area per unit time)

14. Flux also depends on distance of an object or observer from the object emitting the radiant energy
Flux of solar energy decreases with distance from the sun.
Relationship is an inverse-square law
Double distance from the sun and intensity of radiation (or energy flux) decreases by a factor of ¼.

15. Temperature Measure of internal heat energy
Rate of motion of molecules in a substance
Faster movement = higher temperature

16. Blackbody radiation
A body that emits radiation over all possible frequencies (remember inversely related to wavelength)
Wavelength distribution depends on the temperature of the blackbody
The Planck function describes the wavelength distribution relative to radiation intensity

17. Wein’s Law Stefan-Boltzmann Law F= sT4 Fig. 3-7 The flux of radiation
emitted by a blackbody
reaches its peak value at
lmax which depends inversely
On the body’s absolute temperature
The energy flux emitted by a blackbody
is related to the fourth power of the
body’s absolute temperature
Stefan-Boltzmann Law
F= sT4
Fig. 3-7

18. Blackbody emission curve for sun and earth – note higher energy
UV Vis IR (heat)
Energy flux and blackbody
radiation temp. are related.
Because it is hotter, sun emits
more energy per unit area at all
wavelengths.
Changes in energy flux determine the
spectrum of the EM radiation emitted.
Shifts along the l axis.
Blackbody emission curve for sun and earth – note higher energy
shorter wavelength (higher frequency) emissions for the sun.

19. Energy output of the sun
Predicts a maximum of radiation emission in the visible region (0.4 – 0.7 mm)
Large component of high energy UV (remember this is damaging)
Assume Earth is a blackbody radiator
The Earth System responds to both the amount of solar radiation and its EM spectrum

20. Earth’s energy balance
If temperature is constant, the planet has to be in radiative balance

21. Fig. 3-19 Earth’s globally averaged atmospheric energy budget.
Energy input = energy output
Some incoming solar radiation is lost before reaching the earth’s surface (30%).
Some is returned to space as IR (70%)
Fig Earth’s globally averaged atmospheric energy budget.

22. Some incoming solar radiation is reflected by clouds
Plus CO2 and H2O
Some incoming solar radiation is reflected by clouds
Some is absorbed in the atmosphere (ozone at low l; CO2 and H2O at high l)

23. Fig. 3-8 Blackbody emission curves for the Sun and Earth.
UV Vis IR (heat) O3
H2O, CO2
Fig Blackbody emission curves for the Sun and Earth.

24. O3
Plus CO2 and H2O
Only 50% if incoming solar radiation gets through the atmosphere to the Earth’s
surface

25. Net effect of atmosphere on incoming and outgoing radiation
Blackbody radiation of the sun minus that “lost” in the atmosphere.
Solar spectrum clipped
at high and low ends
Energy loss shifts lmax to lower wavelengths when energy is re-radiated by the Earth.
Reradiated as IR (heat).
Assumes
Earth is a
blackbody
radiator.
Shift in lmax
controlled
by Wein’s law
Net effect of atmosphere on incoming and outgoing radiation

26. Outgoing IR also absorbed by greenhouse gases.
CO2 and
H2O
Outgoing IR also absorbed by greenhouse gases.

27. Greenhouse gas absorption
Major role in warming atmosphere
Traps heat
Leads to re-distribution of radiation before it is re-radiated to space
Without greenhouse gases, planet would be much colder (~ -20oC)

28. Feedback loops
Feedback between lithosphere, hydrosphere, atmosphere and biosphere interact to maintain relatively constant, favorable temperatures over most of geologic history

29. Greenhouse effect
Planetary energy balance in the absence of a greenhouse
Simple model
Planet with no atmosphere and albedo that of Earth
Energy emitted by Earth= energy absorbed by Earth
From distance of sun, Earth is a circle (projected area)
Energy absorbed = energy input – reflected light
Albedo is the average color of the planet
Low albedo = dark color = absorbs heat (warms up)
High albedo = light color = high reflectance (cools down)
Assuming blackbody radiation, Stefan-Boltzman law predicts the temperature of the atmosphereless planet

30. calculate area of a circle Apply Stefan-Boltzman Law and simplify
Where S is solar flux
A is earth’s albedo
We know how to
calculate area of a circle
Apply Stefan-Boltzman Law and simplify
Box Fig. 3-1

31. Low albedo = low reflectivity (light is absorbed)
High albedo = high reflectivity
Fig. 2-6

32. Box Fig. 3-1

33. Box Fig. 3-1

34. Treat atmosphere as black body
T4e = (S/4)*(1-A)
Energy balance
T4s = 2T4e
Fig. 3-2 The greenhouse effect of a one-layer atmosphere.
Provides 33oC of surface warming

36. Fig. 3-19 Earth’s globally averaged atmospheric energy budget.