ANTH 1010 Lecture 2: Gaining a Historic Perspective on Climate Change

• School: UConn
• Department: Anthropology
• Course: ANTH 1010
• Professor: Eleanor Ouiment

Document Summary

Natural!causes!of!climate!change:!volcanic!eruptions,!ocean!current,!the!earth"s! orbital!changes,!and!solar!variations: volcanic&eruptions&k!when!a!volcano!erupts!it!throws!out!large! volumes!of!sulphur!dioxide! (so2),!water!vapor,!dust,!and!ash!into!the! atmosphere. , large!volumes!of!gases!and!ash!can!influence!climatic!patterns!for! years!by!increasing!planetary!reflectivity!causing!atmospheric!cooling. , tiny!particles!called!aerosols!are!produced!by!volcanoes;!because! they!reflect!solar!energy!back!into!space!they!have!a!cooling!effect!on! the!world, ocean&current&k!the!oceans!are!a!major!component!of!the!climate! system,!with!ocean!currents! (functioning!like!rivers!within!the!ocean)! moving!vast!amounts!of!heat!across!the!planet. , winds!push!horizontally!against!the!sea!surface!and!drive!ocean! current!patterns. ! Interactions!between!the!ocean!and!atmosphere!can!also!produce! phenomena!such!as!el!ni o!which!occur!every!2!to!6!years. : deep!ocean!circulate!cold!water!from!the!poles!towards!the!equator! and!move!warm!water!from!the!equator!back!towards!the!poles. , without!this!movement!the!poles!would!be!colder!and!the!equator! warmer. , the!oceans!play!an!important!role!in!determining!the!atmospheric! concentration!of!co2. , earth&orbital&changes&k!earth!makes!a!full!orbit!around!the!sun! yearly. ! It!is!tilted!at!an!angle!of!23. 5 !to!the!perpendicular!plane!of!its!orbital! path. : changes!in!the!tilt!of!the!earth!can!lead!to!small!but!climatically! important!changes!in!the!strength!of!the!seasons,!more!tilt!means! warmer!summers!and!colder!winters;!less!tilt!means!cooler!summers! and!milder!winters. , solar&variations&k!the!sun!is!the!source!of!energy!for!earth"s!climate. , although!the!sun"s!energy!output!appears!constant!from!an!everyday! point!of!view,!small!changes!over!an!extended!period!of!time!can!lead! to!climate!changes. , some!scientists!suspect!that!a!portion!of!the!warming!in!the!first!half! of!the!20th!century!was!due!to!an!increase!in!the!output!of!solar! energy. , scientific!studies!demonstrate!that!solar!variations!have!performed!a! role!in!past!climate!changes:!e. g. ,!a!decrease!in!solar!activity!was! thought!to!have!triggered!the!little!ice!age!(1650!and!1850). If!you!go!even!further!back!in!time,!to!the!point!when!earth!was! young,!our!sun!was!only!emitting!about!70%!of!the!energy!it!gives!off! today. !: at!that!level,!it!would!at!first!seem!that!all!water!on!earth!should!have! frozen,!but!we!know!from!deposits!that!this!was!not!the!case,!there! was!liquid!water!on!earth, this!puzzle!is!called!the! faint!young!sun!paradox , one!explanation!is!that!there!was!more!heatktrapping!c02! (perhaps! from!volcanoes)!in!the!atmosphere,!although!volcanoes!can!cause! cooling!by!shooting!sulfur!dioxide!into!the!upper!atmosphere!where!it! deflects!incoming!sun!energy, ultimately!as!the!sun!got!older!and!brighter,!c02!levels!dissipated,!and! temperatures!stayed!warm!from!solar!energy. Just!prior!to!the!last!major!land!extinction! (the!dinosaurs),!volcanoes!appear! to!have!caused!a!massive!ocean!extinction!of!life!forms. : this!was!during!a!period!of!extensive!volcano!eruption!in!places!like!what!we! today!call!india!and!lasting!for!100,000!years, scientists!studying!fossils!from!seymour!island!near!antarctica!have! identified!an!unusually!thick!bed!of!sediment,!where!more!sediment!than! normal!accumulated!in!each!time!period, researchers!believe!they!have!evidence!from!the!fossils!in!these!sediment! layers!of!two!extinctions!that!killed!off!species!of!snails!and!clams!living!on! the!ocean!floor, for!example,!while!one!species!of!amonite!became!extinct!in!the!first!phase,! the!remaining!six!became!extinct!in!the!second!phase, this!is!an!evidencekbased!case!of!greenhouse!gas!buildkup! (from!volcanoes),! leading!to!a!warming!environment! (in!the!oceans)!and!resulting!species! extinction. Past&impacts&of&climate&change: during!the!course!of!human!history,!relatively!sudden!climate!changes!also! have!occurred,!with!notable!impact! (and!potential!lessons!for!our!current! situation), one!period!of!importance!in!this!regard!is!known!as!the!younger!dryas! (nicknamed! the!big!freeze )! America: although!many!key!events!during!the!spread!of!modern!humans!around!the! world!appear!to!coincide!with!favorable!climatic!conditions,!the! incompleteness!of!the!fossil!record!during!the!initial!stages!of!human!arrival! into!different!areas!makes!it!difficult!to!specify!the!precise!effect!of!climate! on!past!human!demography, to!overcome!this!dilemma,!anders!erickson!of!the!department!of!zoology!at! the!university!of!cambridge!and!colleagues!analyzed!the!effects!of!past! climate!change!on!the!demography!of!modern!humans!by!analyzing!the! signals!left!in!the!worldwide!distribution!of!genetic!variation!in!human! populations, migration!of!modern!humans!out!of!africa,!they!argue,!was!blocked!until!60 . 70,000!years!ago,!by!the!particularly!arid!climate!in!northeast!africa!and! much!of!the!arabian!peninsula. : but,!a!combination!of!lowered!sea!level!and!more!favorable!climatic! conditions!about!60k70,000!years!ago!allowed!extensive!migration!of! modern!humans!to!the!arabic!peninsula!and!subsequent!movement!through! an!otherwise!harsh!area, migration!into!europe!of!modern!humans!may!have!been!slowed!by!the! presence!there!already!of!coldkweather!adapted!neanderthals!from!an!even! earlier!migration!of!not!fully!modern!humans!out!of!africa, the!model"s!parameters!suggest!that!climatic!conditions!at!the!end!of!the!last! glacial!cycle!enabled!a!rapid!expansion!into!the!americas,!with!modern! humans!reaching!south!america!about!10,000!years!ago, the!human!species!clearly!survived!past!dramatic!climate!change, but!the!human!species!was!socially!a!very!different!group!than!modern! humans, the!humans!who!survived!and!spread!during!the!ice!age,!lived!in!small! groups,!called!bands,!foraged!for!food,!and!were!as!mobile!as!subsistence! required. Bangkok,!thailand!if!rising!sea!floods!their!cities: still,!it!is!important!to!study!and!understand!how!humans!have!contended! with!climate!change!through!time!and!learn!from!these!cases, the!holocene!is!a!geological!epoch!which!began!at!the!end!of!the!pleistocene! (around!12,000c!years!ago)!and!continues!to!the!present, dendrochrological! (treekring)!and!lake!sediment!records!in!the!american! Southwest!indicates!some!periods!of! megakdroughts !that!were!both!intense! and!persisted!for!decades,!reoccurring!once!or!twice!every!500!years: one!of!these!occurred!over!a!26kyear!period!beginning!in!the!1280s, by!the!beginning!of!this!period,!people!who!we!today!call!the!anasazi!had! established!southwest!settlements!characterized!by!elegant!stone!and!adobe! buildings!in!semikarid!and!highland!areas, at!the!height!of!their!power!in!the!late!eleventh!century,!the!chaco!anasazi! dominated!a!territory!in!the!american!southwest!larger!than!any!european! principality!of!the!time. , a!vast!alliance!of!hamlets!and!towns!integrated!the!region!through!economic! and!religious!ties,!and!the!whole!system!was!interconnected!with!hundreds! of!miles!of!roads. , but!many!of!these!settlements!were!abruptly!abandoned!near!the!end!of!the!