Heating the Earth

1. Heating the Earth Insolation, terrestrial radiation, convection, conduction, radiation, albedo, aspect and greenhouse effect Geography 12 – Ms. Inden

2. How is the Earth heated • Energy makes things move • Radiationfrom the sun is energy • Radiant energy moves in waves or rays • The shorter the wavelength, the more energy • Radiant energy can be reflected by or absorbed by objects • The atmosphere and the earth are absorbing and also reflecting heat energy • When the energy is absorbed, molecules in objects to move, therefore creating heat • Radiant energy powers the water cycle and wind

3. Conduction http://www.qrg.northwestern.edu/projects/vss/docs/thermal/1-how-does-heat-move.html • Heat energy is transferred to matter (the atmosphere the ocean, or the earth’s surface) • The molecules and atoms in the matter start to move, and they in turn bounce into other molecules, cause heat to move through the object

4. What is Air Pressure? • Important concept for weather! • Air pressure is the weight of air • The atmosphere has areas of high and low pressure • Why? • Gravity pulls air down • Weight of the column of air pushes down on the lower air

5. Convection • Convection is when a substance that can flow (like water and air), is heated IN THE PRESENCE OF GRAVITY • It creates a cycle of rising and falling matter • This moves heat energy around the ocean and the atmosphere

6. Why don’t the tropics get hotter and hotter, and the poles colder and colder? • Remember that the earth’s tilt on its axis (23.5 degrees) keeps the poles tipped away or toward the sun during the sun and winter respectively • This difference drives atmospheric circulation as the heat moves from the surplus at the equator to the deficit at the poles • Air pressure is different in cold and warm air masses and it wants to equalize – from the highs to the lows – more on this later • This movement also takes place during night and day changes in temperature • It also occurs as temperature differences exist over land and water next to each other • The scientific principle here is convection – warm air rises, cools, and falls back to earth

7. Insolation • Remember that insolation is solar radiation that is received by the earth’s surface http://pilotgcseradicalgeography.co.uk/2006/10/09/why-is-antarctica-cold/

8. Why doesn’t the earth just keep getting hotter? • Energy is absorbed, but it is also reflected back into space

9. Short wave Long Wave http://mrsdlovesscience.com/greenhouse/greenhouse.html

10. http://greenerloudoun.wordpress.com/climate/

11. Figures are variable (how thick is the cloud cover, how much water vapour is in the atmosphere, etc) • 24% is absorbed by the atmosphere • Clouds reflect about 23% (and absorb 3%) • About 45% of incoming radiation reaches earth’s surface • 24% as direct • 21% as diffuse radiation – this happens because the radiation is first deflected by molecules in the atmosphere and is SCATTERED in all directions. Some of this scattering reaches the earth’s surface • Terrestrial (earth) radiation is when the earth radiates the heat back out into the atmosphere • Only 4% of this reaches outer space

12. Follow the link to look at the natural and human-made greenhouse gases • http://mrsdlovesscience.com/greenhouse/greenhouse.html

13. What is albedo • A ratio that describes how reflective an object is • How much light is absorbed or reflected by the surface • Fresh snow has a high albedo • Dark objects have a low albedo • The earth has a wide variety of surfaces that also change with the seasons or human activity. • Albedo matters to how much heat energy is absorbed by the earth’s surface • If the surface reflects heat, evaporation does not occur, thereby impacting the formation of cloud and precipitation • In areas that have been deforested or over-grazed by cattle, the albedo becomes higher, thereby causing a reduction of precipitation and a greater likelihood of desertification

14. Take a look at the text • Look at and draw the diagram on page 15.4 on page 246 that shows the consequences for the natural environment of the fact that air cools as it rises • Read on the same page about anomalies (something that is different than you would expect) with regard to the fact that mountain tops are colder than valley bottoms – this is called an inversion. Take note of what an inversion is in your book. • The diagram on the next page – Fig. 15.6 is a good look at why the heat on the earth’s surface and air pressure cause higher elevations to be cooler. Copy this diagram into your notes. • It is important to understand the idea of microclimates (p. 252). Please note that the textbook uses the term exposure for aspect. Aspect is which compass direction a slope of a hill faces. Obviously, a slope that faces the sun will be warmer than a slope that lies in the shade. If a valley is facing in the direction of the prevailing winds will also be cooler because the wind will blow away the heat radiating off the earth. • Urban microclimates – Take a few notes on heat islands (cities) – give several important reasons why cities are hotter than the surrounding country-side. What are some city planners doing to solve these problems?