Announcements Announcements The Ethics and Climate Change Conference was really The Ethics and Climate Change Conference was really interesting! interesting! http://depts.washington.edu/ponvins/ecc/program.htmlhttp://depts.washington.edu/ponvins/ecc/program.htmlDepartment social tomorrow afternoonDepartment social tomorrow afternoonsee web page; see web page; http://www.atmos.washington.edu/2007Q2/211/http://www.atmos.washington.edu/2007Q2/211/No extraNo extra--credit seminars this weekcredit seminars this weekExtra credit problem may still be handed in by Extra credit problem may still be handed in by WednesdayWednesdayExam handed back tomorrow Exam handed back tomorrow Poster list updated by tomorrowPoster list updated by tomorrowRead Chapter 14: Pleistocene Read Chapter 14: Pleistocene GlaciationGlaciation(Ice Ages) (Ice Ages)Silicate Weathering Silicate Weathering ““ThermostatThermostat””Key Points1. Weathering goes faster with higher CO22. Higher CO2, leads to warmer climate and more freshwater runoff—both increase rate of weathering3. Colder climates, less freshwater runoff, less weathering—atmospheric CO2builds up from volcanic degassingSilicate Weathering FeedbackSilicate Weathering FeedbackInitial ForcingCO2+Silicate Weathering Rate+-Temperature/ Precipitation+Negative Feedback—Stabilizing ClimateClimate ForcingsClimate Forcings Solar activityFaint early sunSnowball earth Earth-sun positionIce agesAerosolAerosolVolcanismVolcanismAsteroid impactsAsteroid impactsGreenhouse warmingGreenhouse warmingSummary of snowball earthSummary of snowball earthClimate models (and our simple feedback analysis) Climate models (and our simple feedback analysis) suggest that there is an instability in our climate system suggest that there is an instability in our climate system that would produce an icethat would produce an ice--covered planet (snowball)covered planet (snowball)What could trigger the instability?What could trigger the instability?Reduction in greenhouse gas concentrations, especially Reduction in greenhouse gas concentrations, especially coupled with a fainter sun (about coupled with a fainter sun (about --6% in Neoproterozoic)6% in Neoproterozoic)Possible trigger is not clear Possible trigger is not clear ––have to reduce COhave to reduce CO22levels levels and CHand CH44levelslevelsContinents all clustered at equator Continents all clustered at equator ––more weathering?more weathering?Source of CHSource of CH44exhausted and CHexhausted and CH44removed by photolysis?removed by photolysis?More summary:More summary:Ice formation increases from poles, cutting off biologic Ice formation increases from poles, cutting off biologic activity in ocean (changes activity in ocean (changes 1313C ratio)C ratio)Planet freezes over Planet freezes over ––life survives but barelylife survives but barelyVolcanism continues Volcanism continues ––COCO22gradually builds upgradually builds upEventually get enough large enough greenhouse effect Eventually get enough large enough greenhouse effect to begin melting iceto begin melting icePositive feedback => rapid melting of snowballPositive feedback => rapid melting of snowballVery high COVery high CO22atmosphere would promote weathering, atmosphere would promote weathering, producing lots of carbonate rocksproducing lots of carbonate rocksThis would draw down COThis would draw down CO22, producing some sort of , producing some sort of climate equilibriumclimate equilibriumMore summary:More summary:Wild explosion of life in this new warm, wet world Wild explosion of life in this new warm, wet world (Cambrian explosion, 540 m. y. before present)(Cambrian explosion, 540 m. y. before present)Geological evidence supports the idea of snowball earthGeological evidence supports the idea of snowball earthEvidence of worldEvidence of world--wide glaciations (continents all in tropics wide glaciations (continents all in tropics ––magnetic data)magnetic data)Rapidly formed carbonate rocks above glacial tillRapidly formed carbonate rocks above glacial tillBanded iron formationsBanded iron formationsCould we have a snowball earth today?Could we have a snowball earth today?Caldeira and Kasting, Nature (1992)Modern EarthIncreasing CO2Climate ForcingsClimate Forcings Solar activityFaint early sunSnowball earth Earth-sun positionIce agesAerosolAerosolVolcanismVolcanismAsteroid impactsAsteroid impactsGreenhouse warmingGreenhouse warmingPleistocene Ice AgesPleistocene Ice AgesFormation of earthEarliest evidence of life –prokaryotic bacteriaRise of atmospheric oxygenEarth freezes over? – life survives in small pockets?Cambrian explosion of life –beginning of fossil recordAsteroid impact – end of dinosaursModern ice-ages beginEnd of last ice-age – rise of human civilization““ErraticsErratics””––Pipestone National Monument, MinnesotaPipestone National Monument, MinnesotaWhat happens during a glacial period?-- Temperature drops-- Ice cover on land (and maybe ocean, but we don’t know) extends equatorward-- Sea level drops (increased water mass on land); 130 m (400 ft) for last ice age-- Amount of land mass increases-- Land compresses (due to huge weight of ice)How do we know about ice ages?How do we know about ice ages?Geological evidence (pretty good Geological evidence (pretty good ––dealing with dealing with last 500,000 to 1,000,000 years)last 500,000 to 1,000,000 years)Ocean sediment coresOcean sediment cores1818O fraction O fraction ––accurate measure of ice amountaccurate measure of ice amountOther climate markersOther climate markersVery precise datingVery precise datingIce coresIce cores1818O fraction O fraction ––record of local temperaturerecord of local temperatureCO2 and other gases in ice bubblesCO2 and other gases in ice bubblesO18 / O16 Climate SignalO18 / O16 Climate SignalO16 is O16 is ““normalnormal””oxygen; O18 has two extra neutrons => oxygen; O18 has two extra neutrons => heavierheavierWater (H2O) can have either O18 or O16Water (H2O) can have either O18 or O16Takes energy to evaporate water, more energy to Takes energy to evaporate water, more energy to