1Astro 101: Planetary AtmospheresDec. 11, 2008Depletion of the Earth’sOzone layer: 1979 - 2004Please watch thismovie while waitingfor lecture to begin.The color bar belowindicates the amountof ozone: RED = high amount (good),BLUE = low amount(bad!)The Ozone Hole over Antarctica19791998• “From September 21 to 30,2006, the average area of theozone hole was the largestever observed, at 10.6 millionsquare miles,” said PaulNewman, atmospheric scientistat NASA’s Goddard Space FlightCenter. Newman was joined byother scientists from NASA andthe National Oceanic andAtmospheric Administration(NOAA) in reporting that theozone hole over the polarregion of the SouthernHemisphere broke records forboth area and depth in 2006.• ”These numbers mean theozone is virtually gone in thislayer of the atmosphere,” saidDavid Hofmann, director of theGlobal Monitoring Division atthe NOAA Earth SystemResearch Laboratory.2006: The worstyear ever for theozone holePRS Question: How were these maps ofthe atmospheric ozone obtained?Much of these data were collected by“TOMS”, the “Total Ozone MappingSpectrometer”1. NASA has airplanes flyingaround the atmospheremeasuring the amount of ozone2. NASA has balloons floating inthe ozone layer collectingsamples3. NASA observes the spectrumof the atmosphere with atelescope2Alaskan Glaciers showingsome small changes...McCarty Glacier 19092004!Alaskan Glaciers showingsome small changes...Muir Glacier 1941Alaskan Glaciers showingsome small changes...Muir Glacier 2004Evidence of decreasing ice in the Arctic Sea:19792003RED: open ocean in 2003CYAN: sea ice still present but amount substantially reducedWe see that global warming is happening. What isthe impact?3Scuba NYC!• By 2100, the Earth couldbe 2 or 3 degrees Celciuswarmer• When the Earth waspreviously that warm, theocean levels were 80 feethigher• This would take a fewhundred years to occurnow, but are you sureyou want to build a newstadium for theYankees??Satellite imageof Martha’sVinyardModel of the sameregion after theoceans rise by3 feetThe Effects & Benefits ofan Atmosphere• Pressure. The right combination ofpressure and temperature allows liquidwater to exist on the surface of a planet.• Greenhouse effect. Boosts thetemperature at the surface of a planet.Increased temperature is beneficial for life.• Absorption & scattering of light.Prevents harmful X-rays and ultravioletlight from reaching the surface.• Weather.4Venus, Earth (and even Mars):Molecular Atmospheres• Not including Mercury and the Moon, thedensities of terrestrial atmospheres are highenough so that the vast majority of the atomsbond together to form molecules• Venus: 96% CO2, 3.5% N2• Earth: 77% N2, 21% O2, a bit of argon andgaseous water• Mars: 95% CO2, 2.7% N2, some argon...• Titan: 90% N2, ...but no O2. The rest is hydrogencompounds, including poisonousstuff for life as we know it. Interaction of light with atmospheric matter• X-rays. Lots of energy;can ionize most atoms andbreak most molecules.• Ultraviolet. Can ionizeatoms only some of thetime, but can break manymolecules• Visible. Mostly ignored(transmitted) by matter;sometimes scattered• Infrared. Frequentlyabsorbered by moleculescausing them to rotate andvibrateWhat happens when thesunlight arrives at a planet?• Some light is just reflected/scatteredaway, e.g. by clouds.• X-rays and UV light is absorbed. Thisusually results in conversion to someother form of energy or light, e.g., aUV photon ionizes an atom resulting ina moving free electron with kineticenergy.• Visible light reaches the surface andis absorbed by the ground, whichheats the ground.• The ground is a dense,opaque object. When it isheated, it produces athermal radiationcontinuum spectrum. Itstemperature producesINFRARED THERMALRADIATION.The heated ground reradiates thermal radiation in the infrared.e-UV lightMolecules absorb light and convert itinto rotational and vibrational energy• Infrared light canbe absorbed by amolecule causing itto rotate or vibrate.• Energy in rotationaland vibrationalmotions can bereadily converted toheat in the gas.Molecular spectrumNOTE: molecules can emit and absorb many more wavelengths than single atoms5The Greenhouse Effect1. Visible sunlight heats the ground.2. The ground re-emits the light asinfrared thermal radiation.3. Infrared light does not passeasily through the atmosphere!!4. IR light is absorbed bygreenhouse gases, moleculessuch as water (H2O), carbondioxide (CO2), and methane(CH4).5. Rotational and vibrationalmotions of the molecules heatthe atmosphere.The Killer Greenhouse Gas:CO2The Greenhouse Effect changes theequilibrium temperature of theatmosphere1. The greenhouse effect does nottrap energy in an atmosphereforever.2. It takes longer, but eventuallyenergy escapes back out to space.3. Atmospheres attainequilibrium. The input andoutput of energy comes intobalance.4. Like a blanket on a sleepingperson, the greenhouse effectelevates the equilibriumtemperature of the atmosphere.Large amounts of greenhouse gases are produces byproducts of industrial societies, e.g., automobiles, coal-,oil-, and gas-burning power plantsThe GreenhouseEffect• An atmosphere is like agreenhouse• Main greenhouse gases: water(H2O), carbon dioxide (CO2),and methane (CH4)• Since the onset of the industrialrevolution, there is no doubtthat the amount of CO2 in theatmosphere has increaseddramatically.• The Earth’s temperature isstrongly correlated with thequantity of greenhouse gases(Atmospheric CO2 measured from ice cores drilled in the Antarctic) Some things torealize about thegreenhouse effect• On human timescales, ittakes a while for greenhousegas levels to drop• If all human production ofCO2 stopped today, badeffects would likely continuefor 30 years...• How?? Replace coal plantswith nuclear power?Brown: CO2Pink: temperatureCurrentlevels2100projectionNOW160,000 years ago6Global warmingis correlatedwith theincreases ingreenhousegases caused byhuman use offossil fuelsWithout an atmosphere andthe greenhouse effect that itcauses, the average surfacetemperature of the Earthwould be roughly 0o FTHE EARTH WOULD BECOVERED WITH ICE!Average surface temperatures ofterrestrial planets with atmospheres-50 C-55 C25%Mars(1.52 AU)15 C-17 C36%Earth(1.00 AU)470 C-43 Celcius72%Venus(0.72 AU)ActualtemperatureNogreenhousetemperatureReflectivityPlanetWhat about ozone? What’sthat all about?Ozone (O3) is poisonous to humans.At sea level, it is one