long term changes/ice ages

geological background in quaternary

last 2-3myr been global cooling, fall sea level, rising biodiversity in the Cenzoic.

factors of long-term environmental change.

terrestrial factors

• factors operate on diff timescales

• tectonics- long time scales, millions years

• climate- multiple time scales, from seasonal, decadal, millions, centurys etc

• human- sharp increase in last 200 years, anthropocene, short term changes but also relatively long

terrestrial:

• atmospheric composition

• plate tectonics

• human activity

• surface albedo

atmoispheric composition changes:

• volcanism, thru aerosols in abrupt events, release co2, so2, h20, particulate matter. creates volcanic winters.

• biochemical evolution: reactions in atmosphere, like the increasing oxygen in atmospehre to 23% from 1% 600myr ago via photosynthesis. biosphere removes carbon frm atmosphere, but also releases in respiration. climate n biosphere r coupled.

• greenhouse gases: co2 conc 0.04% today, increased via humans, volcanos,

plate tectonics:

• continental drift alters ocean n atmospheric circulatuon. e.g change from pangea to modern day.

• Closure of Darian Gap 3.5myr reduces transport of warm water into atlantic

• rise of tibet

• opening of southern oceans (38myr) caused antarctic ice sheet to form

• causes topography changes that influence atmospehric circulation (rise of tibet)

• effects spatial pattern of albedo

• flora/faunal migration limits n distribution

Human activities

• emissions since 19th centruy (industrial rev) effects global n local climate.

• role of agriculture spread into europe

• major firs in tropical savannahs for 1000s years as seen by soil charcoal sites

• altered terrestrial vegetation n hydrological patterns for millenia

factors of long term environmental change

extra terrestrial factors

pt 1

variations in solar output:

• maunder minimum and dalton minimum

• 11 year sunspot cycles

• monthly wolf sunspot number

• global temp correlations w sunspot cycles n solar irradiance proxies

extra terrestrial factor long term change

orbital theory

• Croll 19th Century recognised earths orbit varies thru time, with milankovitch calculating orbital dynamics for last myr.

• Imbrie and Imbrie, 1986: Insolationn cause sig global climate change, accounting for quaternary glacial cycles

• eccentricity (circular to eliptical every 96kyr), obliquity (tilt 21.5-25 degree every 42kyr), precession (wobble axis trace cone every 21kyr, precession of equinox)

precession:

• determines seasons in each hemisphere, when earth at perihelion (closest), currently N.Hem in winter at perihilion but 10.5kyr ago N hem summer at perihilion. This cud explain deglaciation at end of Younger Dryas 11ka

combined variations of each orbital forcing creates insolation forcing that varies with lattitude

orbital predications:

• ETP curve summarises combined global effect of orbital variations on the insolation forcing. (lowe and walker, 2015)

does explain quaternary variations:

• eccentricity variations r too weak to explain large scale temp fluctuations of glacial-interglacial cycles

• observed periodicities also changed from 40kyr to 100kyr around 900ka

• doesnt explain cenzoic cooling (10-50myr)

• doesnt explain initiation of quaternary

• also sub 10kyr fluctuations which r unexplained

evidence on corresponding impacts of changes on terrestrial flora n fauna

mannion, 1999: biodiversity trends

tallis, 1991: evidence of change, redwood.

• palm, evidence of change

quaternary glacial-inter vegetation cycles (Reille et al, 2000)

sea level quaternary changes tied to global ice volume, increased selectivitu meaning faunal species extinctions n migrations were rapid. (Miller et al, 2005)