The Earth’s Global Energy Balance

1. The Earth’s Global Energy Balance • What is it? • The difference in the flow of energy reaching • the Earth’s surface and the flow of energy • emitted by the Earth’s surface. • Radiation • Insolation over the Globe • Composition of the Atmosphere • The Global Energy System • Global Energy Budgets of the Atmosphere and Surface • Net Radiation, Latitude and the Energy Balance

2. Everything that has a temperature emits radiation

3. Electromagnetic Radiation • Hotter objects emit more energy at shorter wavelengths

4. The Earth’s Global Energy Balance • Radiation • Insolation over the Globe • Composition of the Atmosphere • The Global Energy System • Global Energy Budgets of the Atmosphere and Surface • Net Radiation, Latitude and the Energy Balance

5. Insolation over the Globe • Insolation (incomingsolarradiation)- is the flow of solar energy intercepted by an exposed surface • Varies by latitude and by date

6. Insolation depends on the angle of the sun above the horizon.

7. Insolation over the Globe Figure 2.6, p. 57

8. Insolation over the Globe • Annual Insolation is greater at lower latitudes (closer to the equator) • High latitudes receive much less solar energy (the annual insolation at the poles is about 40% of the value at the equator

9. World Latitude Zones

10. The Earth’s Global Energy Balance • Radiation • Insolation over the Globe • Composition of the Atmosphere • The Global Energy System • Global Energy Budgets of the Atmosphere and Surface • Net Radiation, Latitude and the Energy Balance

11. Composition of the Atmosphere • The atmosphere consist of air. • What is Air? Air is a mixture of various gases • Earths atmosphere extends about 10,000 KM above the earth • 97% of the atmosphere lies within 30 KM of the Earth’s surface Between 0 and 80KM the composition is pretty uniform…

12. Constant gases in the Troposphere • Nitrogen 78% (converted by bacteria into a useful form in soils) • Oxygen 21% (produced by green plants in photosynthesis) • Carbon dioxide (CO2) (0.035%) • used by green plants during photosynthesis produced by respiration and burning of fossil fuels Composition of the Atmosphere • Argon ~1%

13. Composition of the Atmosphere • Other Variable atmospheric gases include: • Water vapor = 0.1 - 4% • Methane (produced by cows, termites, swamps etc.) • - Dust and particulates (from pollen, sea-salt, volcanic dust, soil, etc.) • Ozone • CFCs (entirely human-made gas)

14. Composition of the Atmosphere Ozone (O3) - Ozone in the stratosphere (35-55km) absorbs ultra violet (UV) radiation

15. Composition of the Atmosphere • Ozone can be destroyed: • Chemicals (CFC’s) created by humans contact Ozone oxygen and cause a chemical reaction turning O3 into O2 (regular oxygen); this leaves less molecules to absorb UV rays If Ozone is reduced, UV absorption is reduced

17. IG4e_02_p65 Every 1% decrease in global Ozone=2% increase in Ultraviolet radiation Ozone holes due to aerosols (man made and natural)

18. The Earth’s Global Energy Balance • Radiation • Insolation over the Globe • Composition of the Atmosphere • The Global Energy System • (Sensible Heat and Latent Heat Transfer) • Global Energy Budgets of the Atmosphere and Surface • Net Radiation, Latitude and the Energy Balance

19. Sensible Heat and Latent Heat Sensible heat – the quantity of heat held by an object that can be sensed by touching or feeling Conduction: Direct transfer of heat or energy from one object to another (in the direction of decreasing temperature) Convection: When a warmer substance (water or air) moves into the space of a cooler substance warming that area.

20. Sensible Heat and Latent Heat • Latent heat (“hidden heat”)- heat that is used and stored in molecular motion when a substance changes state. The heat cannot be measured by a thermometer.

21. Evaporation and Latent Heat • Energy is required to overcome the molecular forces of attraction between particles of a liquid, and bring them to the vapor state, where attractions are minimal. • To change liquid to water vapor, energy is absorbed into by individual molecules, these molecules get so energetic that they break the hydrogen bonds connecting them to other water molecules;  Ultimately becoming molecules of water vapor.

22. Latent Heat Each time water changes state, energy is absorbed or released. Latent heat is important in moving large amounts of energy from one region to another

24. The Earth’s Global Energy Balance • Radiation • Insolation over the Globe • Composition of the Atmosphere • The Global Energy System • (Sensible Heat and Latent Heat Transfer) • Global Energy Budgets of the Atmosphere and Surface • Net Radiation, Latitude and the Energy Balance

25. The Global Energy System • Energy Flows from the Sun to the earth and then back out into space • Involves radiant energy flow AND energy storage and transport. • Radiation is absorbed and diverted through scattering by dust/molecules, cloud reflection, albedo and more…

26. The Global Energy System Albedo - percentage of solar radiation reflected by any surface. - fresh snow = 85-95% - dry sand = 35-40% - tropical forest = ~13% - Earth’s average albedo = ~30% Light Surfaces (ice/snow) Albedo values Dark surfaces (pavement)

28. The Earth’s Global Energy Balance • Radiation • Insolation over the Globe • Composition of the Atmosphere • The Global Energy System • Global Energy Budgets of the Atmosphere and Surface • Net Radiation, Latitude and the Energy Balance

29. Global Energy Budget • Global energy budget of the earth’s atmosphere and surface must balance over the long-term (energy arriving=energy leaving) • Radiation/energy is reflected and absorbed by the atmosphere and the earth • The earth loses energy through the emitting of long wave radiation, latent heat transfer and sensible heat transfer

30. Global Energy Budgets of the Atmosphere and Surface 49% of insolation = direct radiation (radiation that goes directly to Earth’s surface) 31% of insolation reflected back to space 20% of insolation absorbed by the atmosphere

32. Global Energy Budgets of the Atmosphere and Surface • Under clear skies, 80% of insolation may reach the ground • Under cloudy skies, only 45 to 10% of insolation may reach the ground

33. Greenhouse Effect:

35. The Earth’s Global Energy Balance • Radiation • Insolation over the Globe • Composition of the Atmosphere • The Global Energy System • Global Energy Budgets of the Atmosphere and Surface • Net Radiation, Latitude and the Energy Balance

36. Net radiation is the difference between incoming and outgoing radiation Net Radiation, Latitude and the Energy Balance Incoming Outgoing

37. Net Radiation, Latitude and the Energy Balance • Energy amount varies dependent upon latitudinal position • Between 40°N (and S) and the poles (90°N and S) the net energy is negative • Equatorially between 40°N and 40°S there is a positive net energy Negative net energy Positive Net Energy

40. The Earth’s Global Energy Balance • Radiation • Insolation over the Globe • Composition of the Atmosphere • The Global Energy System • Global Energy Budgets of the Atmosphere and Surface • Net Radiation, Latitude and the Energy Balance