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:

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