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?

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

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)

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

Mt. Barriers (Orogenic Uplift)

WINDWARD SIDE

•Warm air is pushed up by mountain, condenses, & precipitaties

•WET

LEEWARD

•Dry Air on opposite side

•Desert - like

Cascade Mts. – Washington State

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).

Global Pressure Systems Influence Climate

Global Ocean Currents

Gulf Stream Current – Circulates warmer tropical water north (Britian is warmer than it should be at its latitude)

CH. 24.7 Climate Change: Seasonal: El Nino Natural Short Range Change in Climate

El Nino year

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)

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

Icehouse vs. Greenhouse

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ICE HOUSE = Ice present @ poles

GREEN HOUSE= NO ice present @ poles

HIGH 18O:16O

LOW18O:16O

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)

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

Ice Ages: Cause

5. Change in Thermohaline Circulation (melting sea ice changes salinity of water; no sinking = slow down of THC) change climate.

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