northern hemisphere climate variability over the past few hundred years: proxy-based reconstructions...

Northern Hemisphere Climate Variability

over the Past Few Hundred Years: Proxy-based Reconstructions of the winter NAM and PNA

Justin J. Wettstein

John M. [email protected]

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Climate Impacts Group Seminar January 4th, 2005

N.H. Climate Variability over the Past Few Hundred Years: NAM/PNA Reconstructions

OUTLINE

NAM ? PNA ?

Existing Proxy-based Reconstructions

A more parsimonious approach

Where from here?

NAM ? PNA ?


Northern Annular Mode (NAM)Pacific North America [pattern] (PNA)

PNA:Sea Level Pressure

NAM:Sea Level Pressure

Max in both figures is ~6 millibars per unit change in the NAM / PNA index


NAM: Temperature / Precipitation 1

Max is ~1.8º C per unit change in NAM Max is ~1 cm/month per unit change in NAM

Temperature(red = warm)

Precipitation(red = dry)


NAM: Temperature / Precipitation 2

Max is ~1.8º C per unit change in NAM Max is ~1 cm/month per unit change in NAM




PNA: Temperature / Precipitation

~ -1.5 to 0.6ºC per unit change in PNA Max is ~1 cm/month per unit change in NAM



Flip sign: sorry!


Time Series of the NAM / PNA

Existing Proxy-based Reconstructions


Proxies with annual resolution

Source: International Tree Ring Database (various)

Source: NOAA Paleoclimatology Program (various)


NAO Reconstructions: Summary

[Jones and Mann, 2004 (Reviews of Geophysics: Fig 6b)]

Jones+ 1997: Observed NAO (1821-Present)

Luterbacher+ 2002: Multi-proxy, documentary records, met data (1500-1990)

Cook+ 2002: Multi-proxy (1400-1979)

Vinther+ 2003: Greenland ice cores (1250-1970)

Others: Appenzeller+ (1998), Gluek and Stockton (2001), Cullen+ (2001)


NAO Reconstruction: 1 example

Cook et al., 2002 (J. Climate)


Cook et al., 2002: Proxy weights


PNA-like Reconstruction

Moore et al., 2002 (Nature)

See also: Minobe, 1997 (GRL)

Accumulation vs. time at site


PDO reconstruction: example(s)

Biondi et al., 2001 (J. Climate)

Others: Gedalof and Smith, 2001 Evans et al., 2000

Urban et al., 2000 Linsley et al., 2000


PDO meta-reconstruction: example

Gedalof et al., 2002 (GRL)

• PC-based reconstruction of the PDO index using 5 existing reconstructions

• PC1 kept, PDO correlation is 0.64 from ~1900 - 1990

• “PDO may not have been an important organizing structure during the 19th century” SST regression

A more parsimonious approach


Approach

1. Species-by-species

2. Trees must lie in a region where the temperature and/or precipitation signal of the NAM / PNA is robust

3. Growth of a particular species must be significantly and consistently related to temperature or precipitation during the winter preceding the annual growth ring

4. Ring width time series must be available 1711-1971 so only one statistical model is required

5. Each candidate predictor must add to both the calibration and cross-validated skill of the model, or it is removed


Good locations: NAM temperature


Good locations: NAM precipitation


Bad locations


Prior winter proxy skill: monthly

Black Pine: Mediterranean Temperature (good proxy)

Norway Spruce: Mediterranean Temperature (poor proxy)


Poor seasonal correlations: 2 ex.

Scots Pine Minimum Density temperature correlation

Camp century temperature correlation


Depends on where you look

Norway Spruce Temp. Correlation Norway Spruce Precip. Correlation


Good seasonal correlations

Good trees / ring widths(temperature examples)

milcent

Good ice core(temperature)


Summary of results

Where from here?


Frequency dependent 1


Frequency dependent 2

correlation


Future Work

66 annually-resolved records from ice cores– Local temperature correlations up to 0.55– Local precipitation correlations up to 0.55– NAM index correlations up to 0.55 – PNA index correlations up to 0.60

– Best correlations generally from low-pass filtered ice data– Possibility to “staple” two reconstructions together?

Match cross-validation method to Cook et al., 2002 and compare with NAO reconstruction directly– Simplified NAM and PNA (not shown) reconstructions seem

comparable to existing literature (x-valid r’s ~0.65 and ~0.60)

Other suggestions?

northern hemisphere climate variability over the past few hundred years: proxy-based reconstructions...

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