ch. 24.7: climate & climate change objectives: 1. what factors affect climate? 2. what is el...
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Ch. 24.7: Climate & Climate ChangeObjectives:1. What factors affect climate?2. What is El Nino & how does it work?3. What causes ice ages? 4. How can scientists determine climate changes of the past?
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Climate = Long term weather of a region
Depends on temperature & precipitation
6 Climate Regions:Tropical: Hot & wet or Hot w/ wet & dry seasons
Dry: Desert
Temperate marine: humid w/ mild winters
Temperate continental: cold, snowy winters
Highlands: mt. regions, cool & wet
Polar: tundra & ice cap
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Climate: Factors Affecting Temperature1. Altitude: Cooler @ higher altitudes
2. Latitude: – Cooler as you move away fr. equator. – Same latitudes have similar temps (solar radiation)
3. Distance from bodies of water: – Water moderates temps. less variation
• Landlocked areas – more extreme temps. (Hotter summers & colder winters)
4. Ocean currents can influence temps.Warm current milder winters (Gulf stream brings warmer temps to UK)
Cold current cooler summers (California current brings cooler summer to San Francisco)
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Climate: Factors Affecting Precipitation.1. Latitude
Tropical air holds more moisture rainy2. Distribution of air pressure systems & global winds
a. High Pressure Areas Dry sinking air (30 N& S and poles)b. Low Pressure Areas Moist rising air (0 & 60 degrees)b. Global Winds
Wind from sea: Carry moist air Wet climateWind from land: Dry Climate
3. Mt. BarriersMts. Force warm moist air from sea up condenses & precips. on one side of Mt. Dry on other side
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Mt. Barriers (Orogenic Uplift)
WINDWARD SIDE
•Warm air is pushed up by mountain, condenses, & precipitaties
•WET
LEEWARD
•Dry Air on opposite side
•Desert - like
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Cascade Mts. – Washington State
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Orogenic Uplift
Note how the western side of the Cascade Mts. (windward) are green with vegetation. The eastern side of the Cascades (leeward) are brown – due to a lack of vegetation (It’s dry on this side of the mountain).
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Global Pressure Systems Influence Climate
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Global Ocean Currents
Gulf Stream Current – Circulates warmer tropical water north (Britian is warmer than it should be at its latitude)
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CH. 24.7 Climate Change: Seasonal: El Nino Natural Short Range Change in Climate
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El Nino year
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El Nino: Periodic warming of water in the central & eastern Pacific Ocean (off coast of Peru)
Normally this water is VERY COLD due to an upwelling from the deep ocean.
• Warm water affects atmosphere above water & trade winds slacken
• Ocean currents in Pacific weaken or reverse direction
Result: Abnormal weather
When: Every 8 yrs (average)
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Climate Change: What Causes a Planet to Warm Up or Cool Down?
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Climate Change: Ice AgesNaturally Occuring, Long Term
Ice Age: Colder than usual & glaciers cover larger portion of Earth’s surface as they advance fr. poles.
When:4 major ice ages in last 2 million yearsLast one ended 10, 000 yrs ago
http://www.pbs.org/wgbh/nova/ice/chill.htmlhttp://courses.missouristate.edu/EMantei/creative/glg110/glaciers.html
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Icehouse vs. Greenhouse
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ICE HOUSE = Ice present @ poles
GREEN HOUSE= NO ice present @ poles
HIGH 18O:16O
LOW18O:16O
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www.atmo.arizona.edu/.../sec5/robust.html
Causes of Ice Ages1. Milankovitch Cycles = Changes in incoming solar radiation due to variations in Earth’s orbit, tilt, or wobble.
A. Change in “eccentricity” of orbit(How elliptical or circular our orbit is. Varies from 0 – 6% elliptical; Now: 1.7% elliptical)Cycle: 100 000 years
More elliptical = more variation in climate = ice ageB. Changes in Tilt Ranges from 22 – 24.5 degrees (Now 23.5 degrees)More Tilt = more seasonal variation = ice ageCycle: 41 000 yrs
C. Changes in Wobble (direction of axis). N. Pole pointed toward or away from sun? Cycle: 23, 000 years
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Causes of Ice Ages continued2. Volcanic Activity
Dust & ash can cause cooling in short term by blocking solar radiation (ice age)
Volcanic gases cause warming over long term (b/c they are greenhouse gases)
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3. Changes in Solar Radiation (solar cycles)
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Ice Ages - Cause
55 Ma: Uplift of the Himalayas4. Changes in continental arrangements
(Plate tectonics) can change ocean currents or air flow can change climate
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Ice Ages: Cause
5. Change in Thermohaline Circulation (melting sea ice changes salinity of water; no sinking = slow down of THC) change climate.
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6. Biology Driven Ice Age = Snowball EarthWeaker sun (30% weaker) + Arrival of photosynthesizing bacteria (removing CO2 from atmosphere) = ICE •ICE has high albedo --> more solar radiation reflected --> less energy absorbed --> MORE ICE•Volcanic GHG eventually warm planet up
Ancient Ice Age: Snow Ball EarthIce covered Earth ~ 2.4 bya (end of Precambrian Time)
Global temps: ~ - 74 F