Lectures 14 & 15
Lectures 14 & 15 GC 170A
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This 4 page Class Notes was uploaded by Gigi on Tuesday October 27, 2015. The Class Notes belongs to GC 170A at University of Arizona taught by E. Bigio in Fall 2015. Since its upload, it has received 20 views. For similar materials see INTRO TO GLOBAL CHANGE in Global Studies at University of Arizona.
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Date Created: 10/27/15
Lectures 14 amp 15 Natural Climate Variability Climate Climate Change Climate Variability Instrumental Records Temperature measuring methods Paleoclimate reconstructions Proxy Methods Why is it important to study paleoclimate Hockey Stick Diagram Ice Cores How are Ice Cores collected Greenland Ice Cores Average of many year39s worth of weather for a location Long Term changes in the regional climate or earth39s average temperature occurring over decades to centuries not only warming Short term changes in the climate occurring over years to decades usually related to natural climate in uences Satellites weather stations on land ocean weather ba oons Last 150 years Representation of climate temp or precipitation in the past Prior to instrumental methods Tree rinds ice cores pollen records ocean sediments corals Past Key to future is to understand the past Historical info provides a context for recent warming Climate of past 1000 years hockey stick dramatic warming in past few decades The smaller uctuations represent climate variability Done through glaciers and ice sheets Shows past atmosphere composition amp temperatures Can get temperature C02 Methane and Particulate Matter They contain older layers of ice w air bubbles containing evidence of C02 levels in past Drill Tent in Greenland cores kept cold and own to ice core facility in NZ or US Denver Layers Firn Ice Compact Ice Bedrock More snow that falls faster ice sealed amp air bubbles are trapped In the lab Ice Water Oxygen Isotope Analysis Isotope Isotopic Change Gas Bubbles Particulates Scientists Vostok Ice Core amp Dome C Tree Rings Dendrochronology Ice is cut into sections Ice is melted Gas bubbles are released Water is collected Gas Water Dust amp Particles are measured 99 Ntquot Temperature hydrogen amp oxygen isotopes Type of water isotopes Gives clues about temperature at time of deposition Atoms of the same element with a different number of neutrons different mass Evaporation lighter 16O evaporates more easily atmospheric H20 vapor is less in 180 than oceanic water Condensation heavier 180 are precipitated faster than lighter 16O Coldest snow is lightest Contain samples of the atmosphere Carbon Dioxide Methane Nitrous Oxide Dust ash from past volcanic eruptions amp pollution Take samples of modern atmosphere amp ice accumulation near location of the ice core Compare air bubbles with modern C02 measurements Shows repetitive cycles or uctuations in C02 amp unprecedented C02 levels in recent decades Distinct growth band that represents one year of growth Trees grow from the inside out youngest rings on the outside Dating and study of annual rings in trees Dendros growth of tree rings Chronology record of events Ring Ring Width Complacent Tree Growth Sensitive Tree Growth Crossdating Why not just count the rings Bristlecone Pine Trees Temperature Sensitive Moisture Sensitive Skeleton Plot Composed of early wood amp latewood Boundaries are marked by transition between dark latewood cells and the early wood cells of the next ring Distinct Rings in the winter the tree shuts down amp stops growing In the desert it is not cold enough to form distinct rings Related to changes in temperature or precipitation Wide Ring Wet year Narrow ring dry year Growing near a local water source have no variation in growth stream channel Growing on steep slopes amp rock areas represent regional changes in rainfall want to study shows a variation between wide amp narrow rings Pith center of the tree Bark outside Method of tree ting analysis trees from the same region which are sensitive to the same environmental variable precipitation or temperature can be matched with other trees Tree ring patterns are matched between multiple samples or sites used to determine how old a sample is need at least 50 rings Trees can have false rings or missing ringsdry years Very old grow at high elevations in White Mountains of California used for temperature reconstructions Show 1 Cooler global temperatures for 12 years narrow rings and 2 Cold Snaps for 12 weeks frost rings At higher elevations growth is limited by cold temps Warm summerslonger growing seasonwide rings Cold summersshorter growing seasonnarrow rings At lower elevations trees are limited by precipitation Wet winters wide rings Dry winters narrow rings Represents the narrow tree rings in a sample to cross date Ring Width Index Plot Time series plot showing trends in ring width tree growth over past 250 years Frost Rings Row of damaged cells in the middle of a tree ring happens to temperature sensitive trees at high elevation in cold temperatures