Chapter 17 Climate

I. What is Climate? A. Climate Vs. Weather Weather is the condition of the atmosphere at a particular time Climate is the average weather condition in an area over a long period of time

B. Latitude Distance north or south from the equator The higher the latitude is, the colder the climate tends to be The amount of direct solar energy a particular area receives is determined by latitude

The sun’s rays hit the equator directly, at almost a 90° angle The sun’s rays strike the poles at a lesser angle than they do the equator

C. Seasons Seasons happen because the Earth is tilted on its axis at a 23.5° angle The tilt affects how much solar energy an area receives as Earth moves round the sun

1. Summer - Northern Hemisphere is tilted toward the sun and receives more direct sunlight and thus experiences warmer temperatures and longer days - Southern Hemisphere has colder temperatures and shorter days

2. Winter - Northern Hemisphere is tilted away from the sun and receives less direct sunlight and thus experiences cooler temperatures and shorter days - Southern Hemisphere has warmer temperatures and shorter days

D. Prevailing Winds Winds that blow from one direction Affect the amount of precipitation that a region receives If the prevailing winds form from warm air, the air cools and loses the ability to hold water vapor, bringing moisture If the prevailing winds form from cool air, the air warms up and gains the ability to hold water vapor, bringing dry conditions

Winds that travel across large bodies of water absorb moisture Winds that travel across land tend to be dry

E. Mountains As elevation increases, temperature decreases 1. The Wet Side Mountains force air to rise As air rises it cools down, releasing moisture as snow or rain The land on the windward side is usually green and lush

2. The Dry Side As dry air crosses the mountain, the air begins to sink As air sinks, it warms up and gains the ability to hold water vapor The land on the opposite side of the windward side is usually desert-like This side of the mountain is in a rain shadow

F. Large Bodies of Water Waters high specific heat causes it to absorb and release heat slower than land does Large bodies of water help to moderate the temperatures of the land around it

G. Ocean Currents Surface temperature of the water affects the temperature of the air above it Warm currents heat the surrounding air and cause warmer temperatures Cool currents cool the surrounding air and cause cooler temperatures

H. Climates of the World Three major climate zones – tropical, temperate, and polar Several types of climates in one zone due to differences in geography and the amount of precipitation

II. The Tropics The tropical zone extends from about 23.5° north latitude to 23.5° south latitude Receives the most direct solar radiation, causing hot temperatures Three major biomes that differ in the amount of precipitation, soil characteristics, vegetation, and kinds of animals

A. Tropical Rain Forests Warm and wet weather Little difference between seasons Greatest plant and animal diversity of any biome Poor soil

B. Tropical Savannas Very warm climate Have a dry season that lasts four to eight months Soils are nutrient poor Plants include tall grasses, scattered trees, and thorny shrubs

C. Tropical Deserts Receives less than 25 cm of rainfall per year Hot deserts are caused by cool, sinking air masses

III. Temperate Zones Experience seasonal change Receive less solar energy than latitudes in the Tropics do

A. Temperate Forests High amounts of rainfall and seasonal temperature differences 1. Evergreen Forests Trees that keep their leaves year-round

2. Deciduous Forests - Trees that lose their leaves at the end of the growing season - Soils are fertile because of the organic material in decaying leaves

B. Temperate Grasslands Receive too little rain for trees to grow Most-fertile soils of all biomes

C. Chaparrals Vegetation is mainly evergreen shrubs Rocky, nutrient-poor soil

D. Temperate Deserts Cold deserts Drastic change in temperature between day and night

IV. The Polar Zone Located at the North and South Pole Coldest average temperatures of all the climate zones

A. Tundra Long, cold winters with almost 24 hours of night Short, cool summers with almost 24 hours of daylight Permafrost, or permanently frozen soil, lays underneath thawed soil

B. Taiga Evergreen needle-leaved trees called conifers - Flexible branches allow heavy snow to fall off without damaging the tree - Contain acidic needles that drop and make the soil acidic

V. Changes in Climate A. Ice Ages The geologic record indicates that the Earth’s climate has been much colder than it is today An ice age is a period during which ice collects in high latitudes and moves toward lower latitudes

1. Glacial Periods Enormous sheets of ice advance Large amounts of water freeze, causing sea levels to drop

2. Interglacial Periods Warmer periods between glacial periods Ice begins to melt and the sea level rises again We are currently in an interglacial period that started 10,000 years ago

3. Motions of the Earth The Milankovitch theory proposed that changes in the Earth’s orbit and in the tilt of the Earth’s axis cause ice ages

4. Plate Tectonics One theory proposes that ice ages happen when the continents are positioned closer to the polar regions

B. Volcanic Eruptions Send large amounts of dust, ash, and smoke into the atmosphere that act as a shield The shield blocks some of the sun’s rays, which causes the Earth to cool

C. Asteroid Impact When asteroids hit the Earth, they send up debris, blocking sunlight and thermal energy

D. The Sun’s Cycle The sun follows an 11-year cycle, changing from a solar maximum to a solar minimum When the sun is at its solar maximum, it produces a larger percentage of high-energy radiation

E. Global Warming The Earth’s natural heating process, in which the atmosphere traps thermal energy is known as the greenhouse effect An increase of carbon dioxide in the atmosphere increases absorption of thermal energy An increase in temperature will cause polar ice caps to melt and cause flooding