Proxy Measures of Past Climates

1. Proxy Measures of Past Climates • Current News & Weather • Significance of Climate Proxies • Role of Proxies in Reconstructing Past Climate • Limitations and Strengths For Next Class: Read Thompson 2000 Dr. Paul Mayewski on Friday Homework for Monday on AsUlearn Selected slides from: www.mun.ca/geog/courses/rwhite/Lec4.2_MeasuringPastClimate.ppt

6. Driving Question • How and why do scientists reconstruct the climate record prior to the instrument era?

7. Reconstructing Past Climates: Why and How? • Climate reconstruction • Improves our understanding of environmental response to climate variability and climate change • Provides perspective on current climate • Requires identification of a link between quantitative climate forcing and environmental response

8. What kinds of climate proxies can be used to estimate surface temperatures (last 2000+ years)?

9. What kinds of climate proxies can be used to estimate surface temperatures (last 2000+ years)? • Tree rings • Corals • Ocean and lake sediments (varves) • Cave deposits (speleothems) • Ice cores • Pollen deposits • Packrat middens • Glaciers • Documentary evidence (historical records, paintings, etc.)

10. Climate Proxies • Which of the climate proxies excites you the most? Why?

11. How are proxy data used to reconstruct climate? • For most proxies, statistical techniques are used to define the relationship between the proxy measurements and the concurrent instrumental records. • Then, this relationship is used to reconstruct the past climate from the remaining proxy data.

12. Steps involved • Collect proxy data • Dating the proxy data (e.g., matching growth rings of trees to calendar year) • Calibration – usually, this involves using regression to relate the proxy measurement to know climatic conditions • Validation – basically tests the skill of the calibration • Reconstruction – once the proxy/climate relationship is established, we again use regression to predict what past climate was like

13. What are the limitations and strengths of large-scale climate reconstructions? • 1. The instrumental record is short (~100-150 years at most) • 2. The relationship between the proxy data and the climate variable being reconstructed (e.g., temperature) may have varied over time. • 3. There is no consensus among scientists as to which statistical methods/formulae are most appropriate for calibrating and validating the models. • 4. Spatial limitations – collecting proxy data is both time consuming and expensive.

14. Key strengths of proxy measures • 1. Proxy records are meaningful recorders of environmental variables. • 2. Tree ring-derived data are especially valuable in climate reconstruction as they often represent regions (i.e., multiple sites within a region are sampled and replication is a key element of the scientific method). • 3. Most surface temperature reconstructions incorporate proxy data from a variety of sources over wide geographic areas. • 4. The same general trends (e.g., temperature trends) emerge from multiple reconstructions.

15. Questions? • Take out a sheet of paper and write down any questions about the material we covered in lecture this week.