chapter 14 - reconstructing past climates

In order to understand the present and future climates on earth and other planets, we must learn about past climates, what affected them, and how they have changed.

Chapter 14 - Reconstructing Past Climates

Proxy dataany set of non-climatic evidence

collected that is a function of temperature and/or moistureExamples:

•Pollen•Lake levels•Fossils•Chemical isotopes

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Ice cores•Used for centuries as crude climate indicators

•If present = cold; if thicker=more snow; if thinner=warmer and less snow

•First ice cores extracted (1950’s) were used in old ways•1980’s everything changed

•Utilized dust, gases, and chemicals

Oxygen isotopes-paleotemperature proxy

an isotope is an element with extra neutrons in the nucleus of the atom

•Means there is a weight difference•Oxygen has two isotopes

•18O and 16O•16O weighs slightly less so it evaporates more easily when attached to water (H2O)

As ocean water is depleted in 16O, it is enriched (relatively speaking) in 18O.In essence, as we enter a glacial period, ocean waters are enriched in 18O. In ice, 16O is enriched during glacial times.Values are typically presented as a % change or a ratio of 16O/18O, in part because the isotopes are also affected by temperature and can vary in the numeric values.

Greenland ice core-temperature proxy

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Marine Isotope curve- showing stage designations

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Composite Marine Oxygen Isotope Curve

Plants give us a good estimation of past climates due to their immobility and dependence upon precipitation and temperature

•modern climatological classification schemes exploit this

Look for relative abundance of preserved plant remains

Macrofossils- leaves, twigs, bark, etc

Microfossils- pollen and spores

Plots of pollen grains vs depth (time)Pollen plots look to exploit rapid shifts in the types of pollen grains found

•Plants are great colonizers when an ecological niche is unoccupied due to extinction or extantism

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Raw pollen plots- # of pollen grains

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Pollen Plots

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Pollen Plots

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Dendrochronology- study of tree rings

trees record environmental stressThick rings = good growing conditionsThin rings = stressed conditions

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stressed

Non-stressed

Sea level curve (eustatic)Eustasy- a change in the volume of water held in the ocean basinsAs sea rises or falls, landforms are created that give away the former position of water levels

beaches and wave cut platformscoral reefs

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Lake levelsWater accumulates in closed or semi-closed basins

•occurs due to increased precipitation and/or decreased evaporation

As levels rise, landforms are createdAs levels fall, new landforms are createdBoth leave an identifiable record of prior water levels, which reflect moisture in the region

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Lake levels-Lake Bonneville

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Holocene climatic optimum9-7 Kyr bp (7-5000 BC)

•many regions experience a climatic optimum- warm summers mild winters.

Accelerates sea level rise due to deglaciation

Historic records of meteorological events• non-instrumental accounts

•restricted to weird or extreme events•Recorded in literature, birth and death records, art works and theater productions from those time periods.

• instrumental accounts and records•In the renaissance, science became enamored with measuring stuff

•First temperature, then wind, moisture, and pressure

Little Climatic optimum•occurs from about 800 to 1300 AD

•records of civilizations abound in what are now harsh climatic regions

•Greenland- “Norse” colonies•Wari Empire- Peru, South America•Pueblo culture - Chaco Canyon, NM•Anasazi culture- Mesa Verde, CO

•Causes problems in some coastal areas

•Sea level rises flooding places along the Mediterranean Sea

Little “Ice Age”- Occurs from 1350- to 1850 ADProduces cooler weather and forces the termination of all of the cultures mentioned in association with Climatic optimum

ice becomes commonplace in places that do not currently freeze

e.g., Thames River- England