GC 170 1st Edition Lecture 15Outline of Last Lecture I. Climate change over the past 1,000 years i. Medieval Warm Period ii. Little Ice Age II. Natural forcings on climate i. Sunspots ii. Volcanoes Outline of Current Lecture III. Natural Climate Variability IV. Part 2: Proxy methodsCurrent LectureI. Natural Climatea. Extreme warming over the past 50 yearsb. MWP (Medieval Warm Period) and LIA (Little Ice Age)c. Northern Hemisphere temperature reconstructions developed from proxy records i. Tree-ringsii. Ice coresiii. Pollen recordsII. Proxy: a. Data that represents past environments and climates (levels of CO2)i. Before 1958 (Keeling Project) 1. Found levels of CO2 in ice cores2. Contain old layers of ice with air bubbles, containing CO2 levels in pastii. Used to develop paleoclimate reconstructions 1. Key to the future is understanding the past 2. Historical information provides context for recent warming 3. Help predict future environmental conditionsb. Ice Core Methodi. In the lab 1. Ice is cut into sections (10 cm – 1 m) 2. Ice is melted These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.3. Gas bubbles are released 4. Water is collectedii. Scientists measure: 1. Gas a. Samples of the atmosphere reconstruct past greenhousegas concentrationsi. CO2ii. Methane iii. Nitrous Oxide2. Water a. Temperature (Hydrogen isotopes)3. Dust and Particulates in the icea. Dust/ash from past volcanic eruptions and pollutioniii. Shows repetitive cycles or fluctuations in CO2 iv. Shows unprecedented CO2 levels in recent decadesc. Tree ringsi. Distinct growth band that represents one year of growth1. Ring boundaries a. Marked by the sharp transition between dark latewood cells and the early wood cells of the next ringb. In the winter, the tree shuts down and stops growingi. No winter in the desert 1. Rings not as distinctc. There can be false rings so counting rings is inaccurate 2. Ring Widtha. The width of a tree ring is related to changes in temperature or precipitationb. Influences (injury, climate, light/shade, nutrients)3. Tree Growtha. Complacenti. Trees growing near a local water source have no variation in growthb. Sensitivei. Trees on steep slopes and rocky areas represent regional changes in rainfall.ii. The type of growth wanted because ring width is a proxy for past climate conditions1. Variation between width iii. Cross dating: Determine how old a sample is 1. Trees from same region sensitive to the same environmental variable can be matched with other treesii. Dendrochronology: Dating and study of annual rings in trees1. Dendros = growth of tree rings2. Chronos = time 3. ology = the study of iii. Chronology = a record of
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