Chapter 4
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Chapter 4. Global Climates & Biomes. Structure of the Atmosphere. Density decreases as altitude increases (why?) Five layers of gases: Troposphere: 0 – 16 km (10 mi) Weather occurs here Temperatures drop with altitude Stratosphere: 16 – 50 km (10-31 mi)

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Chapter 4

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Chapter 4

Chapter 4

Global Climates & Biomes

Structure of the atmosphere

Structure of the Atmosphere

  • Density decreases as altitude increases (why?)

  • Five layers of gases:

    • Troposphere: 0 – 16 km (10 mi)

      • Weather occurs here

      • Temperatures drop with altitude

    • Stratosphere: 16 – 50 km (10-31 mi)

      • Higher altitudes are warmer (UV light)

      • Ozonelayeris located here

        • Ozone = O3

        • Absorbs UV radiation

    • Mesosphere

    • Thermosphere

    • Exosphere



  • The average weather in a given region over a long time

  • Affected by distribution of heat and precipitation

  • Unequal heating of Earth’s surface:

    • Due to the curvature of the Earth

    • Angle of sun’s rays

    • Albedo: the percentage of incoming sunlight that is reflected from a surface; white reflects, colors absorb

      • Earth’s average = 30%

      • Tropics = 10-20%

      • Snow-covered poles = 80-95%

Atmospheric convection currents

Atmospheric Convection Currents

  • Four properties of air that determine circulation:

  • Density – less dense (warm) air rises

  • Water vapor capacity – warm air can hold more water vapor – max amount is saturation point

  • Adiabaticcooling– air rises  pressure decreases  air expands in volume  expansion lowers air temp

    • Adiabatic heating is the opposite

  • Latentheatrelease– when water vapor condenses into liquid water, energy is released

Formation of hadley cells a type of atmospheric convection current

Formation of HadleyCells: a type ofatmospheric convection current

  • The sun heats moist tropical air, causing it to rise

  • The rising air experiences adiabatic cooling, water vapor condenses into rain which falls back to Earth

  • The condensation of water vapor produces latent heat release, which makes the air expand and rise farther

  • The warm rising air displaces the cooler drier air above it, pushing it to the north and south

  • The cool dry air sinks and experiences adiabatic heating. It reaches Earth’s surface as warm dry air and then flows back toward the equator.

Itcz intertropical convergence zone

ITCZ: intertropical convergence zone

  • The area of Earth that receives the most intense sunlight

  • Dense clouds and intense thunderstorm activity

  • Not at a fixed latitude – moves with the sun’s angle throughout the year

  • Located between 300 N and 300 S

Additional circulation cells

Additional circulation cells

  • Ferrel cells – 300 N & S to 600 N & S

  • Polar cells - 600 N & S to the poles (900 N & S)

Besides all that the earth is spinning

Besides all that, the Earth is spinning

  • The equator rotates faster than the poles…

  • This causes the winds to be deflected – this is the Corioliseffect


And the earth is tilted on its axis

AND, the Earth is tilted on its axis

  • The axis of rotation is angled 23.50 – the latitude that receives the most direct sunlight plus the most hours of sunlight changes throughout the year as Earth orbits the Sun

  • SpringEquinox(March) – Sun directly overhead – all regions get 12 hours of light + 12 hours of dark – spring begins in Northern Hemisphere; fall in Southern Hemisphere

  • SummerSolstice(June) – max tilt of Northern Hemisphere toward Sun – longest amount of daylight – summer begins

  • FallEquinox(Sept) – opposite of March – day & night equal

  • WinterSolstice(Dec) – max tilt of Northern Hemisphere away from Sun – shortest daylight – winter begins

Don t forget about all that ocean water

Don’t forget about all that ocean water!

  • Ocean currents mix all the ocean waters and moderate the temperatures of the continents

  • These are influenced by:

    • temperature, gravity, prevailing winds, the Coriolis effect, & locations of continents

  • Warm water expands – tropical water surface is about 8 cm (3 in) higher  water flows away from the equator

  • Gyres– large-scale patterns of ocean circulation: clockwise in Northern Hemisphere; counterclockwise in Southern

  • Upwellings– along the western coast of continents deeper , nutrient rich water rises – this supports large populations of producers and rich ecosystems

  • Thermohalinecirculation– mixes surface water with deeper water – related to differing salinities

Interaction of atmosphere ocean

Interaction of atmosphere & ocean

  • ElNino-SouthernOscillation

    • Every 3-7 years

    • Surface currents in the Pacific reverse

    • Global impact:

      • Cooler & wetter conditions in SE U.S.

      • Drier weather in southern Africa and SE Asia

Interaction of atmosphere land

Interaction of atmosphere & land

  • Local features can impact climate

  • Rainshadow

    • Mountain range forces air up and over

    • On the windward side, cooler air loses its moisture

    • On the leeward side, air is drier  deserts

Terrestrial biomes

Terrestrial Biomes

  • Biome – an area characterized by typical plants and animals adapted to the yearly temperature and precipitation

  • Each biome contains many ecosystems whose communities are adapted to local variation in climate, soil, and other environmental factors



  • Evaporation > precipitation

  • 30% of Earth

  • Variations in annual

    temp (red) and precip (blue)

    in tropical, temperate, and


Chapter 4

Human Impacts on Deserts

Large desert cities

Soil salinization from irrigation

Depletion of groundwater

Land disturbance and pollution from mineral extraction

Soil destruction from off-road vehicles

Forests enough precip to support stands of trees

Forests – enough precip to support stands of trees

  • Tropical

    • warm temps

    • high humidity

    • photosynthesis


  • Temperate

    • Deciduous forests:

      seasonal changes

      broad leaves dropped for

      cold winters

    • Rain forests:

      evergreens in cool,

      moist environment

  • Polar

    • Taiga

      long, cold winters

      evergreens adapted to

      year-round photosynthesis

Chapter 4

Human Impacts on Forests

Clearing for agriculture, livestock grazing, timber, and urban development

Conversion of diverse forests to tree plantations

Damage from off-road vehicles

Pollution of forest streams

Grasslands less precip fires common soil extremely rich in temperate zone

Grasslands – less precip; fires common; soil extremely rich in temperate zone

  • Tropical


  • Temperate


  • Polar


Chapter 4

Human Impacts on Grasslands

Conversion to cropland

Release of CO2 to atmosphere from grassland burning

Overgrazing by livestock

Oil production and off-road vehicles in artic tundra

Aquatic ecosystems affected by salinity depth and water flow

Aquatic Ecosystems – affected by salinity, depth, and water flow

  • Freshwater systems – low levels of dissolved salts

  • Streams and rivers: from mountains to oceans

    • Flow creates different conditions and habitats

    • Headwaters: cold, clear, rapidly moving water with high levels of O2

    • Downstream: slower moving, less O2, warmer temps, more algae and cyanobacteria



  • Standing water: lakes and ponds

    • Life found in layers – temperature, sunlight, dissolved O2, and nutrient availability changes with depth

    • Littoral zone: shallow area around shore; rooted vegetation

    • Limnetic zone: open offshore area; too deep for rooted plants; food chain begins with phytoplankton

    • Profundal zone: deep water without light; food chain depends on organisms above

    • Benthic zone: muddy bottom; nourished by decaying organic matter



  • Wetlands – land is submerged part or all of the year but is shallow enough for rooted vegetation throughout

    • Swamps: contain trees

    • Marshes: mainly nonwoody vegetation (cattails)

Marine biomes

Marine biomes

  • Estuaries

    • Saltmarshes where rives flow into the ocean

      • Nutrient rich areas due to river flow

    • Mangroveswamps

      • Also produce nutrient rich mud

Marine biomes1

Marine biomes…

  • Intertidal zone

    • Narrow strip between high and low tide mark on the coastline

    • Difficult habitat for life

Marine biomes2

Marine biomes…

  • Coral reefs

    • Warm, shallow water beyond the shoreline

Marine biomes3

Marine biomes…

  • The open ocean

    • Sunlight cannot penetrate to the bottom

    • Photiczone: enough light for photosynthesis

    • Aphoticzone: lacks light and therefore photosynthesis

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