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Atmosphere and Climate
Atmosphere
• Thin layers of gas that surround and protect the Earth
• Makes life on Earth possible– Protects life from harmful radiation
– Allows visible light to reach Earth for photosynthesis
Early Atmosphere
• Poisonous atmosphere that contained helium, hydrogen, carbon dioxide, sulfur dioxide, ammonia, methane, chlorine, nitrogen
• Oxygen was added by producers (cyanobacteria) via photosynthesis, which began about 4 mya
Current Composition of Atmosphere
Layers of Atmosphere
Troposphere
• Extends from Earth to 10km• Contains 90% of atmospheric gases • Most weather occurs in troposphere• Temperature decreases with height
Stratosphere
• From 10km to 50km• Air is less dense and does not have swirling turbulence of the troposphere
• Contains the ozone layer in the upper stratosphere
• Temperature increases with altitude (from ‐80˚ to 0˚C)
Mesosphere
• From 50km – 90km• Temperature decreases with altitude (from 0˚ ‐120˚C) and is the coldest layer of the atmosphere
• Ice clouds occur here • Meteors burn up in this layer
Thermosphereaka Ionosphere • Extends from 90km to between 500 ‐ 1000km
• Outer Space ‐ +100km • Temperature climbs sharply (until about 25km), then increase steadily– Can be about 200˚C hotter during the day– Temperatures range from 500˚ to 2000˚C in the upper thermosphere
– Thermosphere expands when heated, “puffs up”
Thermosphereaka Ionosphere
• Molecules become ionized at these temperatures
• High energy photons from sun remove electrons from gases, creating ions
• Northern and Southern Lights (auroras) – Ions or charged particles collide with atoms and molecules, excit‐ing them to higher energy levels,release colored light as they returnto lower energy levels
Traffic in the Thermosphere
• International Space Station
• US Space Shuttle• Satellites (24,500)
Exosphere
• Extends from about 500km • This is a picture which shows the Earth, its atmosphere (the clouds are likely in the troposphere and stratosphere), the limb of the Earth (the dark blue curve/edge which is the mesosphere and thermosphere), and the dark blue to black region of space (where our exosphere extends out to...). Image courtesy of NASA
Climate• Average weather in a particular area over long periods of time
• Includes:– Temperature data
• Highs and lows, records
– Precipitation data• Totals, highs and lows, records
– Humidity– Wind
• Determines types organisms that are found in an area
Latitude
– Measured in degrees, and is a factor in the amount sunshine an area receives and how intense it is
• Position of Earth as compare to the Equator)– Distance from sun which varies from 147 million km to 156 million km
Tilt of the Earth on its Axis– Causes seasonality – Varies from 21.75˚ to 24.25˚
– Current tilt is 23.5˚– Periodicity is 47,000 years– Large tilt causes warming in poles and smaller temperatures differences in summer hemisphere
Air Circulation
• Properties of air: – Cold air sinks and warms as it sinks
– Warm air rises and cools as it rises
– Warm air holds more moisture than cool air
Air Circulation • Air mass – large body of air that has similar temperatures and moisture content– can be equatorial, tropical, polar, arctic, continental, or maritime
• Air Pressure – 99% of atmosphere is within 32km of Earth and gravity is exerted on it;– Pressure decreases with altitude– Low pressure – cloudy and stormy weather– High pressure – usually means fair weather
Lawrenceville, GA 33.96°N 84°W
Ocean Currents • 2 Types – surface (to 400m) and deep water• Surface currents are caused by:
– Solar heating – causes water to expand, ocean is 8 cm deeper at the equator
– Specific heat of water ‐ oceans hold large amounts of heat, which in turn affects climate
– Rotation of the Earth – causes seasons, changes in amount and intensity of sunlight and changes in temperatures
Ocean Currents
– Winds – blow and move surface water• El Nino – exchange of warm and cool water masses; Eastern Pacific is warmer than normal
• La Nina – Eastern Pacific is cooler than normal
– Gravity – pushes water down a pressure gradient
– Coriolis effect – causes water to move toward the right in Northern Hemisphere
Topography of Local Area
• Elevation – Every 90mrise in elevationequals a 100km shift north in latitude and biome simil‐arity
Rain Shadow Effect
Urbanization and Deforestation
• Heat island effect – pavements and roofs are dry and non‐permeable – Can heat to 27 – 50˚C hotter than air temperature– Strongest effect during the day when the sun is shining
– Remains present at night due to slow release of heat from urban infrastructure
Composition of Atmosphere
• Greenhouse effect – caused by 3 major gases– Water vapor (largest contributor), carbon dioxide and methane
• Ozone layer
Greenhouse Effect– Gases have increased by 25% over last 150 years– Anthropogenic – caused or produced by humans– Natural processes can absorb 6.1 billion metrictons but thereare 3.2 billion metric tons addedeach year
Sources of Greenhouse Gases • CO2:
– Cellular Respiration– Burning of fossil fuels, plants or organic materials– Deforestation impacts CO2 levels because there is less organisms to remove it from the atmosphere; often cleared trees are burned
• Methane – Wetlands, fossil fuels, landfills and livestock – Rice cultivation – waterlogged field are ideal for anaerobic methanogens (growth of bacteria that produce methane) breaking down organic soil matter
Sources of Greenhouse Gases
• Nitrous oxide – fossil fuels, fertilizers, animal waste and deforestation
• Ozone – absorbs infrared energy of the sun at ground level
• CFCs – from foams, aerosols, refrigerants and solvents; break down ozone layer and allow more UV light to reach Earth
CO2 versus Temperature
Greenhouse gases sources in US (2001):
Consequences of Global Warming
• Gradual increase of the temperature of Earth– May increase by 2˚C by 2050
• Oceans will absorb more heat energy, causing hurricanes and typhoons, changing ocean currents, changing rainfall amounts
• Agriculture – some fertile areas may receive less rainfall such as the American Midwest
• Sea levels increase – due to warming of polar regions, coastal areas will flood
Natural Ozone Production
• Formed naturally in the stratosphere by UV radiation – 90% of ozone is in stratosphere
– Absorbs 99% of incoming solar UV radiation
Conditions that Lead to Ozone Depletion
• Ozone layer thinning is primarily over the Antarctic region – In long dark winter over Antarctic, polar vortex forms and isolates cold air
– When temperatures reach ‐80˚C, polar stratospheric clouds of water and nitric acid form
– On the surface of these clouds, CFCs are converted to free chlorine molecules (Cl2)
– When sunlight returns in spring, Cl2 is split into Cl atoms by UV radiation, which then attacks ozone
Ozone Layer Depletion
Consequences of Ozone Depletion • Allows more UV radiation to reach the Earth’s surface– Can damage DNA and cause skin cancer, cataracts, weaken immune systems
Consequences of Ozone Depletion
• Can kill phytoplankton (base of food chains in aquatic ecosystems), and damage developmental stages of fish, shrimp, crabs, amphibians and other animals
• Can cause decreased crop yields, damage to plant form, seeds, nutrient distribution and developmental cycles in plants
Montreal Protocol
• Chlorine atoms remain in stratosphere for long periods of time
• Estimate that 1 chlorine atom can destroy 10,000 molecules of ozone
• International agreement to sharply limit the production of ozone‐destroying chemicals like CFCs– Eliminated most CFCs by 1995– US banned all substances that pose a threat to the ozone layer by 2000
• Considered an environmental success story