Climate of Past—Clues to Climate of Past—Clues to FutureFuture

►Climate has changed in pastClimate has changed in past Humans not presentHumans not present So, why worry about present –So, why worry about present –

►Earth goes through cyclesEarth goes through cycles►Always recoversAlways recovers►Earth warming faster than previouslyEarth warming faster than previously►More COMore CO22 in atmosphere than in previous 600 in atmosphere than in previous 600

k yrsk yrs

Examples of Past Climate Examples of Past Climate ChangeChange

► Glacial periodsGlacial periods See major See major

cyclescycles Smaller cycles Smaller cycles

on large cycleson large cycles

► How do we How do we know?know? RocksRocks FossilsFossils

Other methods for determining Other methods for determining climate of the pastclimate of the past

► Ice CoresIce Cores►Tree RingsTree Rings► IsotopesIsotopes

Gathering Gathering Ice CoresIce Cores

Researchers choose between Researchers choose between weatherports (the semi-cylindrical weatherports (the semi-cylindrical structures consisting of tubular metal structures consisting of tubular metal frames overlaid with insulatory tent frames overlaid with insulatory tent materials) or tents. Weatherports materials) or tents. Weatherports equipped with plywood floors and oil equipped with plywood floors and oil heaters, shared with up to 15 other heaters, shared with up to 15 other scientistsscientists

Ice core drilled at Russian Vostok station in East Antarctica reaches depth of more than two miles and provides information about climate cycles over hundreds of thousands of years. (Schematic courtesy of John Priscu research group, Montana State University)

Todd Sowers, LDEO – Columbia University

Vostok ice core drilling site, Antarctica

•Ice forms in contact with atmosphere•Voids in ice•Voids contain air from atmosphere•With burial, voids closed, gas trapped

http://www.globalchange.umich.edu

Raynaud, 1992

Ice CoresIce Cores

► Show annual layerssShow annual layerss Winter – darkerWinter – darker Summer LighterSummer Lighter

► Must be able to dateMust be able to date Count layers to get Count layers to get

yearsyears► Core must be Core must be

completecomplete

IsotopesIsotopes Ash layersAsh layers

Determining Climate From Determining Climate From CoresCores

►Look at thickness of layersLook at thickness of layers Thick lighter layers = longer summersThick lighter layers = longer summers

►Examine COExamine CO22 in cores in cores COCO22 content changes with climate content changes with climate

Impacts greenhouse effectImpacts greenhouse effect

►More dark layers during cold periodsMore dark layers during cold periods More wind blowing, more dustMore wind blowing, more dust

►We will concentrate on COWe will concentrate on CO22

► Thin cut of a polar ice Thin cut of a polar ice core sample as seen core sample as seen through two polarising through two polarising filters. The dark areas are filters. The dark areas are gas bubbles enclosed in gas bubbles enclosed in the ice the ice (Image: W (Image: W Berner/University of Berner/University of Bern)Bern)

NOAA

COCO22 & Glacial Periods & Glacial Periods

► More COMore CO22 during warm during warm periodsperiods Less during ice agesLess during ice ages Reflect greenhouse Reflect greenhouse

effecteffect► Cycles are about 50-Cycles are about 50-

150 k years150 k years Shorter cycles in Shorter cycles in

betweenbetween► Oceans warmer hold Oceans warmer hold

less COless CO22

► Oceans warmer Oceans warmer release methanerelease methane

► More plants and decayMore plants and decay

Vostok Ice Core RecordVostok Ice Core Record

► From 120,000 to about 20,000 years ago, there From 120,000 to about 20,000 years ago, there was a long period of cooling temperatures, but was a long period of cooling temperatures, but with some ups and downs of a degree or two. with some ups and downs of a degree or two. This was the last Great Ice Age. From about This was the last Great Ice Age. From about 18,000 or 19,000 years ago to about 15,000 18,000 or 19,000 years ago to about 15,000 years ago, the climate went through another years ago, the climate went through another warming period to the next interglacial, - the warming period to the next interglacial, - the current one.current one.

► Fig 1 and Greenland ice cores indicate climate Fig 1 and Greenland ice cores indicate climate oscillations lasting 7,000 - 15,000 years during oscillations lasting 7,000 - 15,000 years during the Last Great Ice Age (110-16 kBP). These are the Last Great Ice Age (110-16 kBP). These are known as �Heinrich events� and are also known as �Heinrich events� and are also evidenced by ocean sediments. A more detailed evidenced by ocean sediments. A more detailed ice core analysis shows an occasional abrupt ice core analysis shows an occasional abrupt change of climate during the last interglacial change of climate during the last interglacial (the Eemian, at 120 kBP), changing by as much (the Eemian, at 120 kBP), changing by as much as 10K during only 10 -30 years. Such changes as 10K during only 10 -30 years. Such changes may be due to switchings of flows in the may be due to switchings of flows in the northern Atlantic. Similar changes have been northern Atlantic. Similar changes have been observed observed at the end of the last at the end of the last glaciationglaciation..

► Fig 1 also shows that carbon dioxide and Fig 1 also shows that carbon dioxide and methane (main greenhouse gases) occur in methane (main greenhouse gases) occur in higher concentrations during warm periods; the higher concentrations during warm periods; the two variables, temperature and greenhouse gas two variables, temperature and greenhouse gas concentration, are clearly consistent, yet it is not concentration, are clearly consistent, yet it is not clear what drives what. The correlation clear what drives what. The correlation coefficient is 0.81 between CO2 content and coefficient is 0.81 between CO2 content and apparent temperature, on the whole. During apparent temperature, on the whole. During deglaciation the two varied simultaneously, but deglaciation the two varied simultaneously, but during times of cooling the CO2 changed during times of cooling the CO2 changed afterafter the temperature change, by up to 1000 years. the temperature change, by up to 1000 years. This order of events is not what one would This order of events is not what one would expect from the enhanced greenhouse effect.expect from the enhanced greenhouse effect.

► Finally, Fig 1 shows that high concentrations of Finally, Fig 1 shows that high concentrations of dust occur at the same times as the colder dust occur at the same times as the colder periods. The most likely reason is that the ice periods. The most likely reason is that the ice sheets were more extensive during colder sheets were more extensive during colder periods, and therefore the sea level lower, thus periods, and therefore the sea level lower, thus there would have been more exposed, bare there would have been more exposed, bare land. land.

Dust concentration, mean temperature (as estimated from the oxygen isotope ratio), CO2 and CH4 concentrations plotted against time, estimated from the analysis of an ice core drilled at the Russian station, Vostok, on the Antarctica plateau

http://www-das.uwyo.edu

Past climatesPast climates

►http://www.globalchange.umich.edu/glhttp://www.globalchange.umich.edu/globalchange1/current/lectures/kling/palobalchange1/current/lectures/kling/paleoclimate/index.htmleoclimate/index.html

Dendrochronology-Tree RingsDendrochronology-Tree Ringshttp://www.sonic.net/bristlecone/dendro.htmlhttp://www.sonic.net/bristlecone/dendro.htmlhttp://web.utk.edu/~grissino/principles.htmhttp://web.utk.edu/~grissino/principles.htm

► Dating of past climate Dating of past climate change through tree ringschange through tree rings Ist used early 20Ist used early 20thth century century

► Wide rings = wet periodsWide rings = wet periods Narrow rings = dry periodsNarrow rings = dry periods

► New wood grows between New wood grows between old wood and bark. old wood and bark. In spring, moisture plentiful, In spring, moisture plentiful,

tree producing new growth tree producing new growth cells. cells.

► first new cells are large, first new cells are large, ► as summer progresses their as summer progresses their

size decreases size decreases in fall, growth stops and in fall, growth stops and

cells die, cells die, no new growth appears no new growth appears

until next spring. until next spring.

Extending DatesExtending Dates► Trees unknown aged matched with tree sequences of known ageTrees unknown aged matched with tree sequences of known age► Can extend ageing to the pastCan extend ageing to the past► Oldest known living thing are Bristlecone TreesOldest known living thing are Bristlecone Trees► By overlapping samples extend dating to 9000 yrsBy overlapping samples extend dating to 9000 yrs► Problem: Ring width depends on environmental factorsProblem: Ring width depends on environmental factors

If environmental factors constant, no ring variabilityIf environmental factors constant, no ring variability The more variable the environment the more the tree rings varyThe more variable the environment the more the tree rings vary

Problem with Ice Cores and Tree Problem with Ice Cores and Tree RingsRings

►Cannot see to far into pastCannot see to far into past Ice cores 650,000 yrsIce cores 650,000 yrs Tree rings 9000 yrsTree rings 9000 yrs

►Earth is 4.6 billion yearsEarth is 4.6 billion years Missing a lot of history of climateMissing a lot of history of climate

►Must use another techniquesMust use another techniques

http://education.jlab.org/faq/index.html

What is an isotopeWhat is an isotope

► Element with same number of protons but Element with same number of protons but with different number of neutronswith different number of neutrons

► Examples: O18, O16, C12, C13, C14Examples: O18, O16, C12, C13, C14

Oxygen IsotopesOxygen Isotopes

► OO22 isotopes: isotopes: 1616O (99.789%), O (99.789%), 1717O (0.037%), O (0.037%), 18180 (0.204%)0 (0.204%)

► 1818O\O\1616O ratio built into shells, minerals. Foraminifers O ratio built into shells, minerals. Foraminifers especially usefulespecially useful

► Important for Quaternary & Late sedimentsImportant for Quaternary & Late sediments► First developed in 1955 (Emiliani)First developed in 1955 (Emiliani)

Copyright Cushman Foundation

Foraminifera in SedimentsForaminifera in Sediments

► Drill in ocean to retrieve Drill in ocean to retrieve cores of sedimentscores of sediments

► Pick the foraminifera outPick the foraminifera out► Analyze oxygen isotopesAnalyze oxygen isotopes► Foraminifera must be Foraminifera must be

well preservedwell preserved► Core must be datedCore must be dated

Forams can be used for Forams can be used for datingdating

Other microfossilsOther microfossils Volcanic ashVolcanic ash

Compare oxygen isotope ratio Compare oxygen isotope ratio to a standardto a standard

►1818O/O/1616O dependent on temp & ratio in waterO dependent on temp & ratio in water► Deviation of ratio compared to standardDeviation of ratio compared to standard

More common standard SNOW = Standard Mean More common standard SNOW = Standard Mean Ocean WaterOcean Water

► Evaporation, lighter Evaporation, lighter 1616O O removed, heavier removed, heavier 1818O remains O remains in waterin water

► Precipitation, heavier Precipitation, heavier 1818O O returned to oceans near coast returned to oceans near coast

► Vapor depleted in Vapor depleted in 1818OO► Also temp dependent, polar Also temp dependent, polar

regions more regions more 1616O locked in iceO locked in ice Oceans depleted in Oceans depleted in 1616O, O,

enriched in enriched in 1818OO► Warmer period, more Warmer period, more 1616O in O in

waterwater► Therefore, changes in Therefore, changes in 1818O O

reflect changes in ice volume, reflect changes in ice volume, sea levelsea level

► Decreased temperature also Decreased temperature also causes more causes more 1818O in shells.O in shells.

► Oxygen, carbonOxygen, carbon, , sulfur, strontium sulfur, strontium vary through timevary through time

► Ocean mixing time Ocean mixing time about 1000 yrs, about 1000 yrs, variations variations considered considered instantaneousinstantaneous

► Timing of variations Timing of variations must be establishedmust be established