Global Climates and biomes Chapter 4 Global Climates and biomes

Atmosphere Weather is short term conditions of atmosphere Climate is long term conditions 5 major processes influence climate/weather: unequal heating of earth, convection currents, Coriolis effect, tilt, and oceans Atmosphere has 4-layers: Troposphere (0-20km): bottom layer, densest, where most weather and mixing occurs, temps get colder with height Stratosphere (20-50km): second layer, gets warmer with height, contains ozone layer that absorbs UV light Mesosphere (50-80km) – third layer, coldest, meteorites burn up Thermosphere – top layer, warmest, absorb gamma rays Atmosphere protects organisms from radiation and it regulates temperatures

Past Climate Study Trapped bubbles in ice cores provide a timescale of: Atmospheric composition, greenhouse gas concentrations, temperature trends Snowfall, solar activity, and frequency of fires Ice cores go back 800,000 years Cores in sediment beds preserve pollen grains and other plant remnants Tree rings indicate age, precipitation, droughts, and fire history http://www.ted.com/talks/lang/en/al_gore_warns_on_latest_climate_trends.html

1. Unequal Heating Atmosphere is heated unevenly for 2 reasons Tilt of the earth Some areas on earth reflect more sunlight than other areas (albedo) White surface has higher albedo than black surface This uneven heating of the atmosphere drives convection currents in the atmosphere

2. Atmospheric Convection Currents Air has 4 properties that determine how it will circulate Density: less dense air rises (warm), more dense air sinks (cold) Water vapor capacity: warm air can hold more water vapor (saturation point) which is less dense Adiabatic heating/cooling: When air rises, pressure decreases and air expands and temps lower due to less friction between air molecules When air sinks, pressure increases and air compresses and temps rise due to more friction between air molecules Latent heat release: when air condenses, the energy that evaporated it is released and air warms

(2). Formation of Convection Currents Air rises in warm, moist tropics Rising air experiences lower atmospheric pressure and adiabatic cooling until it reaches saturation point This leads to condensation which releases latent heat Eventually air cools and spreads out and begins to sink around 30⁰ latitude (deserts) When sinking air hits the ground, it spreads in all directions completing the cycle, called a Hadley cell Air re-converges at the equator, called the intertropical convergence zone (ITCZ) Polar regions cause additional Hadley cells

3. Earth’s Rotation and Coriolis Effect Earth rotates faster at equator than poles Objects’ paths get deflected due to the rotation of earth. This is known as the Coriolis effect This deflects winds and sets up weather patterns Trade winds blow towards the equator between 0- 30°. They meet at the equator and rise creating calm winds called the doldrums Where the air sinks at 30° is the horse latitudes Air moves north from here, Coriolis force deflects it to right, and get westerlies (40°-60°) At poles, the air sinks and moves towards the equator, but gets deflected to right. This creates polar easterlies

4. Earth’s Tilt and Seasons Earth is tilted 23.5⁰ When northern hemisphere is pointed towards the sun they experience summer When northern hemisphere is pointed away from the sun they experience winter (southern hemisphere is opposite) Vernal/automnal equinoxes, everywhere receives 12h daylight Poles have 6 months of darkness and 6 months of daylight

5. Ocean Currents Currents driven by temp, gravity, prevailing winds, Coriolis effect, and continents Water is warmer at the equator, so it expands and rises. This makes the water higher then the rest of earth and gravity takes over Winds and Coriolis effect start ocean currents and deflect them. Called gyres (transport heat) Upwelling (rising of water) occurs along coastlines Thermohaline circulation is when water is saltier, making it more dense, so it sinks ENSO (El Nino – Southern Oscillation– when ocean currents change direction, thus affecting climates (La Nina)

Rain Shadows Air rises on one side of a mountain range and moisture condenses out On other side, air sinks preventing clouds and it remains dry Dry region is called a rain shadow

Altitudes create “latitudinal” patterns Vegetative communities rapidly change along mountain slopes The climate varies with altitude A mountain climber in the Andes Begins in the tropics and ends on a glacier Rainshadow effect = air going over a mountain releases moisture Creating an arid region on the other side

Biomes Biomes are large regions characterized by a specific type of climate and certain types of plant and animal communities Largest category scientists use to classify ecosystems Each biome has many ecosystems Biomes described by vegetation because that determines organisms and amount of vegetation is determined by climate At altitude and latitude increase, temps decrease