Warming the Earth and its Atmosphere

1. Warming the Earth and its Atmosphere Prof. John Toohey-Morales, CCM St. Thomas University Miami Gardens, Florida

2. Temperature and Heat • Kinetic Energy is the energy of motion • Temperature: A measure of a substance’s kinetic energy (a measure of the average speed of molecules) • Heat: Flow of energy from warm to cold • In the atmosphere this is accomplished with conduction, convection, radiation & latent heat

3. Temperature Scales • Kelvin starts at Absolute Zero, where there is no thermal motion • Fahrenheit is “water based” but with 32° freezing, 212° boiling, and 180° between • Celsius is “water based” with 0° freezing, 100° boiling, and 100° between K=C+273 C=5/9x(F-32) F=(9/5xC)+32

4. Latent Heat • Amount of energy required to change a substance from one state to another • Evaporation cools because it must draw energy to occur (also melting and sublimation) • Condensation heats as stored energy in the H2O gas is released when it turns to liquid (also freezing and deposition) • Evaporation-Transportation-Condensation: A way to relocate energy in the atmosphere

6. Conduction and Convection • Conduction occurs at the molecular level and spreads energy from warm to cold • Air is a poor conductor but hot ground can warm a shallow layer of air • Heated air expands, turns less dense and rises as thermals • Convection is a transfer of heat by mass vertical movement of air

7. Radiation • All things above 0°K emit radiant energy • Electromagnetic (EM) waves transport energy which is released after being absorbed by an object • The higher an object’s temperature, the shorter the wavelength of emitted radiation, and the greater the rate of such emissions

8. Radiation (continued) • EM waves from the Sun can travel in a vacuum (no molecules required), are intense, and in the short ultraviolet (UV), visible and infrared (IR) wavelengths

9. Radiation (continued) • EM waves from Earth to space are less intense, not visible, with longer IR wavelengths

10. Absorbing and Emitting Energy • Objects warm when they absorb more energy than they emit, and vice versa • Earth behaves as a blackbody, absorbing nearly all of incoming radiation and emitting nearly 100% of maximum • The Atmosphere is NOT a blackbody but a selective absorber

11. Heat From Below • H20 & CO2 strongly absorb IR radiation, but not solar radiation • Absorbed radiation leads to increase in air temperature • Gas molecules emit IR energy back to Earth • Insulation & Heat

12. Atmospheric Window • Greenhouse gases don’t trap ALL IR radiation as some can escape to space via this “window” • But clouds CAN absorb these IR waves, keeping nights warmer by enhancing the greenhouse

13. Incoming Energy • Only half of the Sun’s radiant energy reaches and is absorbed by the Earth’s surface • 30% is scattered or reflected back to space • 20% is absorbed by atmospheric gases & clouds

14. Energy Balance • Earth and its atmosphere get energy from the Sun as well as from each other • A delicate balance must be maintained if the average temperature of the Earth is to remain fairly constant

16. Orbit and Tilt • Earth is 5 million km closer to the Sun in January but… • January is winter for our hemisphere because of Earth’s 23½° tilt • In January the Sun’s rays strike at a more oblique angle here and a more direct angle in the southern hemisphere • January days are much shorter

17. Winter, Spring, Summer or Fall • Winter Solstice is December 21 when the Sun shines directly above latitude 23½° S • Vernal Equinox is March 20 when the Sun is directly over the equator • Summer Solstice is June 21 when the Sun shines directly above latitude 23½° North • Autumnal Equinox is September 22 when the Sun crosses the equator again

19. Lag in Seasonal Temperatures • Hottest temperatures are not observed on June 21, but in July & August • Earth still absorbing more energy than it’s emitting • When Earth’s IR radiation is in balance with the incoming solar radiation, the highest temperatures are observed • In winter outgoing energy exceeds incoming well past December 21, so it’s colder in Jan/Feb

20. The Sun and Our Surroundings • Objects facing south receive more sun during a year than those facing north

21. Student Activity (due Jan 27) • Draw a simple plan of your house or residence and significant landscaping • Label the compass directions (N, S, E, W) • Observe the Sun, and recall the Sun’s position in the sky throughout the year • Are there design features to reduce heating and cooling costs? • What changes might improve the design as it relates to the incoming solar radiation?