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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

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


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

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


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

Freshwater… water flow

  • 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

Freshwater… water flow

  • 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 water flow

  • 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… water flow

  • Intertidal zone

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

    • Difficult habitat for life

Marine biomes2
Marine biomes… water flow

  • Coral reefs

    • Warm, shallow water beyond the shoreline

Marine biomes3
Marine biomes… water flow

  • The open ocean

    • Sunlight cannot penetrate to the bottom

    • Photiczone: enough light for photosynthesis

    • Aphoticzone: lacks light and therefore photosynthesis