GC 170 1st Edition Lecture 15 Outline 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 methods Current Lecture I II Natural Climate a Extreme warming over the past 50 years b MWP Medieval Warm Period and LIA Little Ice Age c Northern Hemisphere temperature reconstructions developed from proxy records i Tree rings ii Ice cores iii Pollen records Proxy a Data that represents past environments and climates levels of CO 2 i Before 1958 Keeling Project 1 Found levels of CO2 in ice cores 2 Contain old layers of ice with air bubbles containing CO2 levels in past ii 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 conditions b Ice Core Method i 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 collected ii Scientists measure 1 Gas a Samples of the atmosphere reconstruct past greenhouse gas concentrations i CO2 ii Methane iii Nitrous Oxide 2 Water a Temperature Hydrogen isotopes 3 Dust and Particulates in the ice a Dust ash from past volcanic eruptions and pollution iii Shows repetitive cycles or fluctuations in CO2 iv Shows unprecedented CO2 levels in recent decades c Tree rings i Distinct growth band that represents one year of growth 1 Ring boundaries a Marked by the sharp transition between dark latewood cells and the early wood cells of the next ring b In the winter the tree shuts down and stops growing i No winter in the desert 1 Rings not as distinct c There can be false rings so counting rings is inaccurate 2 Ring Width a The width of a tree ring is related to changes in temperature or precipitation b Influences injury climate light shade nutrients 3 Tree Growth a Complacent i Trees growing near a local water source have no variation in growth b Sensitive i 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 conditions 1 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 trees ii Dendrochronology Dating and study of annual rings in trees 1 Dendros growth of tree rings 2 Chronos time 3 ology the study of iii Chronology a record of events
View Full Document
Unlocking...