Paleoclimatology n n Introduction Significance of Climate Proxies

Paleoclimatology n n Introduction Significance of Climate Proxies Role of Proxies in Reconstructing Past Climate Limitations and Strengths For Next Class: Read and Watch Ice Core Videos at: https: //icecores. org/about-ice-cores Selected slides from: www. mun. ca/geog/courses/rwhite/Lec 4. 2_Measuring. Past. Climate. ppt

Driving Question Ø How and why do scientists reconstruct the climate record prior to the instrumental era? © AMS 2

The Earth has exhibited substantial warming over the past ~100 years. Ø Paleoclimatology (the study of past climates), can help place this warming in the context of natural climate variability. Ø Until recently, most reconstructions of climate variations over the last ~1000 years focused on specific locations or regions. Ø

Because widespread, reliable instrumental records are available only for the last~100 -150 years, scientists estimate climatic conditions in the more distant past by analyzing proxy evidence.

Reconstructing Past Climates: Why and How? Ø Climate reconstruction l l l © AMS 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 5

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

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

Deciphering Past Climates © 2018 Pearson Education, Inc. Figure 10. 1

Ocean Sediment Cores © 2018 Pearson Education, Inc. Figure 10. 4

Ice Cores Figure 10. 5 © 2018 Pearson Education, Inc. Figure 10. 6

Corals © 2018 Pearson Education, Inc. Figure 10. 12

Climate Proxies Ø Which of the climate proxies excites you the most? Why? © AMS 12

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. Ø Then, this relationship is used to reconstruct the past climate from the remaining proxy data. Ø

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

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

Key strengths of proxy measures Ø Ø 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.