GEOL 437 Global Climate Change 3/13/18: Introduction to Paleoclimatology

Transcription

1 GEOL 437 Global Climate Change 3/13/18: Introduction to Paleoclimatology What kind of paleoclimate data are out there? What are their strengths and weaknesses? What can we learn from paleoclimatology? Mid semester course evaluations

2 GEOL 437 Global Climate Change 3/13/18: Introduction to Paleoclimatology Key Concepts Superposition Uniformitarianism Stratigraphic correlation

3 Where do paleoclimate data come from? SUPRaNet group ( ); Evans et al (2013)

4 Example: reef corals Environment: temperature,atmospheric and oceanic circulation, nutrients, PAR, seawater chemistry,... Sensor: coral polyp, zooxanthellae Archive: aragonite Veron (2000); painting by G. Kelly Observation: extension rate, ρ, fluorescence, Δ 14 C,Th/U, δ 18 O, δ 13 C, {Sr,Mg,U}/Ca,... Cole et al., 1999; Gagan et al., 2000; Lough, 2004; Cobb et al., 2008; Evans et al 2013

5 How are paleoclimatic reconstructions made? Reconstruction Calibration Validation SUPRaNet group ( ); Evans et al (2013)

6 Paleoclimatology, defined Paleoclimate is climate that existed before humans began collecting instrumental measurements of weather... By analyzing records taken from trees, reefs, glaciers, sediments, and other proxy sources, scientists can extend our understanding far beyond the 140-year instrumental record... the paleoclimate perspective allows us to evaluate climate change many decades and centuries into the past, in order to develop a more reliable estimate of how climate may change [in] the future. -excerpted from the National Geophysical Data Center web pages, c. 2001

7 Paleoclimatology, defined Paleoclimate is climate that existed before humans began collecting instrumental measurements of weather... By analyzing records taken from trees, reefs, glaciers, sediments, and other proxy sources, scientists can extend our understanding far beyond the 140-year instrumental record... the paleoclimate perspective allows us to evaluate climate change many decades and centuries into the past, in order to develop a more reliable estimate of how climate may change [in] the future. -excerpted from the National Geophysical Data Center web pages, c Paleoclimatology: The study of past climates from the traces left behind in the geologic record. It is assumed that the *uniformitarian principle has obtained, but this may not be the case, and the geologic data are always insufficient for paleoclimatological purposes. Dating methods and *paleogeographic reconstructions are suspect, and often *fossil floras and faunas cannot be related easily in terms of time. Most glacial *strata can be dated only within wide limits and many climatic criteria leave no mark in the rocks. -Oxford Dictionary of the Earth Sciences, c. 1990

8 Fidelity of interpretation=f(meas unc, assumptions, calib, proxy, freq, repl, site) Observations: biological, chemical, isotopic data Archive timescales locales Proxy system uncertainty reef corals yr tropics growth rate, δ 18 O=f(T,δ 18 O sw ) chronology min. el. =f(t), 14 C = f(mixing) calibration 'green box' tree rings yr extratropics RW,D=f(T,P,G,D), 14 C, δ 18 O, δ 13 Ccalibration 'green box' ice cores yr poles, high CO 2, CH 4, isotopes, dust, ions,... chronology alt. tropics =f(atm gas conc., T,P, circulation...) spatial scale speleothems yr carb. caves growth rate, δ 18 O=f(P, δ 18 O sw ) chronology packrat yr arid regions macrofossils spatial scale middens lake seds yr lakes, sed color, %CaCO 3, isotopes, chron, calib, anoxic marker species (pollen, macrofossils) chronology, deep sea mar. seds =f(prod(nutr(t)),s), stratigraphy, mixing, sediments yr gl. oceans minor elements = f(t),sea water conc. 'green box' rock record yr gl oceans sed/strat, stable/radioisotopes unconformities hist data yr global(t,x) SAT, SST, SLP, rain,... meas bias, gaps models yr global T,P,u,Φ,ψ,... physics, param,paleo bc/ic's

9 What have we learned about ENSO history? Multivariate ENSO index from historical data standardized anomaly Wolter and Timlin, 1997 (updated)

10 What have we learned about ENSO history? MEI + Pacific SST histories from corals (and tree rings) standardized anomaly Garreaud and Battisti (1999); Evans et al. (2001); Karspeck et al. (2002); Seager et al. (2003)

11 Summary Paleoclimatic information comes from many different types of paleodata, each with unique strengths and weaknesses. They are the only observational means of estimating climates of the past, and when they exhibit simple responses to environmental forcing, may provide the basis for reconstruction of climatically-important variables like temperature and moisture. Uncertainties vary with time, space, frequency, data type, degree of replication, and understanding of the proxy system. Paleoclimatology allows us to place recent observations into a longer term context in a variety of ways. Thurs: Meeting in CHM 1215! Please make a note of it! introduction to EdGCM and HW7 discussion of paleo-streamflow reconstructions for the Upper Colorado basin (Meko et al, 2007); written responses to RFQs due at start of class mid-semester course evaluations response