1. Earth’s Global Energy Balance Overview
Electromagnetic Radiation
Radiation and temperature
Solar Radiation
Longwave radiation from the Earth
Global radiation balance
Geographic Variations in Energy Flow
Insolation over the globe
Net radiation, latitude and energy balance
Sensible and latent heat transfer

2. Overview The global energy system
Solar energy losses in the atmosphere
Albedo
Counterradiation and the greenhouse effect
Global energy budgets of the atmosphere & surface
Climate & global change

3. What is light?
Newton showed that white light is composed of all the colors of the rainbow.

4. Light is an Electromagnetic Wave & a Particle
Photons: “pieces” of light, each with precise wavelength, frequency, and energy.
Our eyes recognize frequency (or wavelength) as color!
Use this slide to define wavelength, frequency, speed of light.

5. Photons Photons – are little packets of energy.
The energy carried by each photon depends on its frequency (color)
Blue light carries more energy per photon than red light.

6. Electromagnetic Spectrum

7. Electromagnetic Radiation
Energy constantly emitted from every surface
Can be in many different forms, e.g. light or heat

8. What happens when light gets absorbed?

9. What causes the atmosphere to be opaque?

10. Solar Radiation Shortwave Radiation from Sun (dark purple)
Absorption of UV by O3
Absorption by CO2 and water vapor (H2O↑) shown as valleys
Longwave Radiation from
Earth (dark red)
Much absorbed by CO2 & H2O↑

11. Scattering Solar radiation can be scattered by atmosphere
Deflected off a molecule, cloud droplet, or particle
May go up toward space, or down toward Earth
Scattering most prevalent in blue wavelengths
Thus, clear, blue skies
Some solar radiation goes directly to surface
Called transmission
Solar radiation arrives as 0.3μm to 3μm wavelengths
This is shortwave radiation

12. Remember you live on a rotating sphere

13. Geographic Variation in Solar Energy
Insolation – Incoming solar radiation
More intense where sun angle is highest
Less intense with lower sun angle
Same energy spread over a larger area

14. Insolation Daily insolation – avg radiation total in 24 hours
Depends on :
Sun angle – higher sun angle → greater insolation
Length of day – higher latitudes get long summer days
Annual insolation – avg radiation total for year
Also depends on sun angle and length of day
Both of these determined by latitude
So, latitude determines annual insolation

15. Net Radiation Energy not usually balanced at any location
Net Radiation - Difference between incoming and outgoing radiation
Between 40°N and 40°S, incoming > outgoing
Creates energy surplus
Poleward of 40°N & S, outgoing > incoming
Creates energy deficit
Deficit = Surplus, so net radiation for Earth = 0

16. Poleward Heat Transport
Surplus energy moves toward poles (deficit regions)
Carried by:
Warm, moist air
Warm sea water
Tropical cyclones
Poleward heat transport is driving force behind:
Global atmospheric circulation
Weather systems
Ocean currents

17. Why are there seasons? The Earth is tilted 23.5° from it orbital plane
Combine tilt with orbit
Northern hemisphere gets more direct Sun part of year (northern summer)
Southern hemisphere gets more direct Sun part of year (northern winter)
Tilt & orbit create seasons, not distance to Sun

18. Northern Summer

19. Northern Winter

20. Solstices & Equinoxes

21. Path of the Sun in the Sky
40° North
June solstice:
Sun rises north of east & sets north of west
Peaks at 73.5° above horizon at noon
15 hours of daylight
Highest daily insolation of year

22. Path of the Sun in the Sky (40° North)
Date
Noon Sun Angle
Daylight
Daily
Insolation
June Solstice
73.5°
15 hrs
460 W/m2
Dec. Solstice
26.5°
9 hrs
160 W/m2
Equinoxes
50°
12 hrs
350 W/m2

23. Path of the Sun in the Sky (Equator)
Date
Noon Sun Angle
Daylight
Daily
Insolation
June Solstice
66.5°
12 hrs
~400 W/m2
Dec. Solstice
Equinoxes
90°
440 W/m2

24. Path of the Sun in the Sky (North Pole)
Date
Noon Sun Angle
Daylight
Daily
Insolation
June Solstice
23.5°
24 hrs
500 W/m2
Dec. Solstice
No Sun
0 hrs
0 W/m2
Equinoxes
Horizon
12 hrs
~0 W/m2

25. Daily Insolation through the Year
Yearly change in insolation greatest toward poles
In Arctic & Antarctic Circles, Sun is below horizon part of year
At Equator, 2 maxs & 2 mins for daily insolation
At equinoxes & solstices
Between tropics, also 2 maxs & 2 mins per year
Yearly insolation change important to climate
Insolation at equinox

26. Annual Insolation by Latitude
Tilted Earth shown as red line
Equator greatest annual insolation
Considerable insolation at highest latitudes
Untilted Earth (blue line)
Highest latitudes little insolation
Big changes in climate
Very cold pole
Massive poleward heat transport

27. Heat Transfer: Surplus energy is transported in two forms
Sensible Heat – can be felt & measured
Transferred by conduction (touching surface)
Transferred by convection (carried by rising air)
Example: Moving air masses
Latent Heat – cannot be felt or measured
Stored as molecular motion when water changes phase
Absorbed in evaporation, melting, and sublimation
Released in condensation, freezing, and deposition
Very important form of heat transfer over long distances
Example: Storm systems, hurricanes
Conduction
Convection
Latent heat absorbed
in evaporation

28. Solar energy losses in the atmosphere
Scattering due to:
Gas molecules
Dust or other particles
O2, O3, & H2O↑ most important absorbers of insolation
Global avg – 49% of insolation makes it to surface

29. Once at the surface what happens? Albedo
Proportion of shortwave radiation reflected
Shown as a proportion (0-1)
Examples:
Snowfield
Black pavement 0.03
Clouds
Water (calm, high angle 0.02), (low angle 0.80)
Avg for Earth and atmosphere

30. So what happens to all the energy absorbed by these various processes?
Counterradiation – heat absorbed by atmosphere reflected down to surface
A – energy radiated to space from surface
B – energy from surface absorbed by atmosphere
C – energy radiated to space from atmosphere
D – Counterradiation

31. Part of Counterradiation is the “Greenhouse Effect”
Longwave radiation absorbed & re-radiated to surface by atmosphere
Lower atmosphere acts like blanket

32. Global Energy Budget
Energy balanced for each level: surface, atmosphere, & space

33. Climate & Global Change
Quantifying human impacts on climate difficult
Climate and society have complex relationship
e.g., Industrial processes
add CO2 to atmosphere (warming)
add aerosols to atmosphere (cooling)