Ice Age EarthA Look at Earths Past Climates

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Earths Climate System

AtmosphereOceanCryosphere; snow and iceBiosphere; plant and animal worldsLand surface

Earths climate is a dynamic system that is driven by energy from the sun and constantly impacted by physical, biological and chemical interactions between the atmosphere, global water supplies, and ecosystems

Energy reaches earth in form of solar radiation

Water vapor, clouds and heat trapping gases create natural greenhouse effect by holding heat in atmosphere and preventing release back to space

Planets surface then warms, increasing heat emitted so that energy released back from earth to space balances what earth receives as visible light from sun.

With human activities today boosting atmosphere GHG levels, earth retatin fraction of energy from sun, raising temperatures---ANTHROPOGENIC CLIMATE CHANGE2

What is Climate Change?

Ask attendees to share examples

What changes in climate have people experienced? Blizzard of 77, drought, etc.3

Humans Experiment with ClimateIncreased concentration of GHGs in the atmosphere due to human activitiesBurning of fossil fuelsDeforestationLandfillsFertilizer useLivestock productionSince the early 20th century, average global temperatures have increased nearly 1.4 degrees FWarming will have widespread impacts on human life and natural ecosystems by 2100

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Atmospheric CO2 levels 1960-2010

Yearly oscillations in the curve reflect seasonal cycles in the northern hemisphere, which contains most of Earths land area. Plants take up CO2 during the growing season in spring and summer and release it as they decay in fall and winter.5

What the Past Tells Us350 years ago the world was in the depths of a prolonged cold spell called the Little Ice Age20,000 years ago, in the middle of the last glacial period, large continental scale ice sheets covered much of North America, northern Europe and northern Asia50,000,000 years ago, global temperatures were so high that there were no large ice sheets at all

Throughout much of its history, Earths climate has alternated between periods of warmth and relative cold, each lasting tens to hundreds of millions of years.

From the perspective of geological time, our planet is currently passing through a relatively cold phase in its history and has been cooling for the past 35 million years

Cold phases, ice sheets covered most of the mid-latitudes, warm phases, forests extended all the way to the poles

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PaleoclimatologyThe study of past climatesAnthropologyGeologyChemistryBiologyAtmospheric ScienceOceanic SciencePhysicsHistory

First evidence to support climate change theories

Fossils of a temperate forest were discovered sandwiched between ice age soil layers

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Evidence to Support Climate ChangeGlacial Erratic

Striations

Banded Iron Formations

First evidence to support climate change theoriesBegan in the Early 1800sPointed to glaciationMisplaced boulders scattered across much of the northern hemisphereLong scratches marked exposed rocks on valley floors

Banded Iron Formations; layers of Banded iron interspersed with chert. Iron only forms in anoxic conditions so our oceans now arent forming iron.

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Timeline of Significant Ice-Ages

Quaternary Glaciation; 2.75Ma-presentKaroo Ice-Age; 360-260MaAndea-Saharan Ice-Age; 460-420MaCryogenian Ice-Age; 850-630MaHuronian; 2.1-2.4Ba

Also during cretaceous, found oldest flowering plant, dating at 122 million years old.. Closest relative is the black pepper plant9

Timeline of Extreme Warming Events

PETM; 66-34MaThe Neoproterozoic; 1000-500MaHuronian Warming Event; 4.6Ba

Cambrian Explosion!

Extinction of Dinosaurs!

Make connection to good and bad for global warming. New life but also death!10

What Causes Ice-Ages and Warm Periods?Dynamic interactions between; Solar outputDistance of Earth from SunPosition of continents and topographyOcean circulationComposition of atmosphere

Variations in Earths orbit, which involve the tilt of the earths pole of rotation and the ellipticity of earths orbit 100,000 41,000, 23,000 year cycles

Talk about plate tectonics briefly!

Positive feedbacks amplify them; albedo and composition of atmosphere11

Cryogenian Ice-Age850-630MaContinents clustered at low-latitudesIce-sheets build up in polar oceansHigh albedo- light reflecting back to space- enhances coolingSea ice reached past 30 degrees latitude and continued to growRun-away albedo effectIce engulfed planet at average depth more than 1km

Change in solar energy and Earths orbit could have caused initial cooling.

Ice sheets form closer to equator, where sunlight is more direct.. More cooling!12

Leaving Snowball EarthThe Geochemical Carbon Cycle

Plate tectonics continueVolcanoes continue to vent CO2Little water would evaporate earths surface so no rainfall to wash CO2 out of atmosphereOver 10Ma, volcanic activity increase CO2 by a factor of 1,000, triggering extreme warmingIntense rainfall and evaporationAccelerate rock weathering, bringing CO2 to normal range

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Why does this matter?What happened?Why did it happen?Has it happened before?Will it happen again?How do we know about it in the first place?

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Paleoclimate DataIsotopic geochemistry; carbon and oxygenDendrochronology; tree ringsPollen Distribution; found in sediments, ice, rocks, caves, etcLake Varves; annual mud layersCoral bed ringsFossilsHuman documents, paintings, evidence of civilization

Preserved physical characteristics of the past that are used to infer and reconstruct past climatic conditions. derived from natural sources such as tree rings, ice cores, corals, and ocean and lake sediments.

These proxy climate data extend the archive of weather and climate information hundreds to millions of years.

The data include geophysical or biological measurement time series and some reconstructed climate variables such as temperature and precipitation.15

Climate Proxy RecordsClimate changes happen at different ratesTransitions can occur within only decades

Temporal (time) and geographical (location) scales.

These proxy climate data extend the archive of weather and climate information hundreds to millions of years.

The data include geophysical or biological measurement time series and some reconstructed climate variables such as temperature and precipitation. Bristlecone Pine: 5400 years old!Oldest dated tree 10,000

Instrumental: Recorded like temperature, amount of rainfall, humidityHistorical: observational rain vs. frost vs. snow, timing of droughts and floods, flowering of trees, migration of birds. 16

What can they tell us?Tree Rings & Dendrochronology- the annual growth rings of trees from mid-latitude climates, where a warm growing season alternates with a winter of dormancy, tell us about temperature, precipitation, and other factors that affect plant growth rates.

Ice Cores- long, cylindrical cores of ice drilled from glaciers and the ice caps of Greenland and Antarctica have annual bands. The layers in the ice tell us about temperature and precipitation. Gas bubbles trapped in the ice provide data about atmospheric CO2 composition in the past.

Sediments from beds of lakes and oceans- Layer thickness can indicate amounts of precipitation or meltwater runoff as rivers carry sediments downstream. Chemical and isotopic composition of the shells of microorganisms embedded in sediments can tell us about the temperatures when those shells were made.

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What can they tell us?Coral reefs- corals form annual growth bands. Analysis of ratios of different types of oxygen in minerals in corals tells us about sea temperatures, although variations in salinity can make these records more difficult to interpret.

Pollen- the amounts and types of pollens found in sedimentary deposits tell us about the types of vegetation found in a certain area at a given time. The vegetation that grows in a place indicates the climate of that place, since different plants grow in differing conditions of temperature, moisture, etc.

Fossils- knowledge of the conditions in which various animals and plants thrive, or at least survive, allows us to use fossils from sedimentary rocks as climate indicators.

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The Sahara wasnt a desert 9,000 years ago.How do we know?

Deep sea sediment cores revealed low salinity= lots of water! When its dry and water evaporates, it leaves behind salt.

Fossil leaf waxes found in ancient lake sediments have low isotopic composition

Pollen records in sediment cores from Lake Tang were of plants that thrive in humid conditions Intense Monsoonal RainsSteppe, covered in grasslands and shrubs. Dotted with large and small lakes

From further research however its transition into the dry climate that exists today happened in just decades!19

~5,200 years agoIt was cold and dry!Preserved plants in Quelccaya ice cap in the Peruvian Andes carbon dated to 5,200 yearsOetzi the Ice-man discovered in Europe in 1991 trapped and died 5,200 years agoTree rings from Ireland and England were at their narrowest 5200 years ago, which suggests the driest period they experiencedIce cores showing two oxygen isotope ratios from the top of Mt. Kilimanjaro in Africa revealed that temperatures 5,200 years ago were very cold!Changes in plant pollen from lakebed cores in South America, lowest levels of methane retrieved from ice cores from Greenland and Antarctica, both occurred 5,200 years ago

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Paleocene Eocene Thermal Maximum55 MaGlobal average temperature of 74FPoles were free of ice-capsPalm trees and crocodiles were found in the arctic circle> 5 degrees C of warming in 15,000-20,000 years

Pangaea in final stages of breaking apartRapid release of Carbon found in sediment cores.Broke apart frozen seafloor releasing extreme amounts of methaneOcean turned acidic, planet warms up dramatically. Extinction of marine foraminifera and difficult for corals. Rapid change in land plants and animals and quick turnover of species.

( Deep sea lake sediments; low oxygen isotopes=warm, decrease in heavy carbon isotopes =release of CO2 in atmosphere )

Warming lasted 200,000 years before earth was able to stabilize again

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PETM as Analog for Current TrendsWarming today is happening ten times as fast!

We are headed for a tripling or quadrupling of CO2 from preindustrial levels

People could argue warmer temperatures bringing new life! But is it happening too quickly for life to adapt?22

Quaternary Glaciations400,000 years ago to Present

CO2 on the rise since the end of the last glacial maximum.. But look how our levels compare with history of Quaternary glaciations!23

NASA Average Global Temperature 1880-2011

4 degree Celsius change24

The Critics.We dont have reliable dataThere is no evidenceGlaciers have always grown and recededOne hundred years isnt enough to give us an accurate measureNot every region of the world is warmingWe cant even predict the weather next weekNatural emissions dwarf human emissionsCurrent warming is a natural trend

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What Can WE do?What is Earths Climatic Fate?

Add new slide for positive!!!26