Cultural Responses to Climate Change: Lessons from the Holocene

Peter deMenocal (Lamont-Doherty Earth Observatory of Columbia University)

Climate - Society Theories

“Cultural Determinism”– Culture alone determines culture.– Prevalent throughout 18th-19th century Europe

“Environmental determinism” – Human culture is determined by the environment.

• Charles Darwin “Origin of Species”, 1870’s  

“Possiblism”– Compromise: The natural environment influences

the range of available (possible) human choices.

Overview

• Natural climate variability: – The present is NOT the key to the past.

• Climate of the last 10,000 years (Holocene):– Punctuated by large and persistent climate

changes every ~1000-2000 years.

• Cultural responses to past climate change: – The Classic Maya and Akkadian empires.

• We can learn about our future by studying the past.

Introduction

• Water availability is the critical factor regulating life in semiarid environments.

• Cultures can and do adapt to interannual to decadal changes in climate.

• How have cultures responded to longer-term (decade to century-scale) changes?

Combine detailed and well-dated paleoclimate and archeological records.

What do we know about the climate of the last 1,000 years?

• Instrumental climate records are too short (100-200 years).

• Longer records of past climate change (paleoclimate):– Glaciers– tree rings – corals – lake and ocean sediments

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Tree-ring record of drought in the American SW

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The 1930s Dust Bowl

• Six year drought (1933-1938), well-documented.

• Due to wanton farming practices and over-capitalization.

• Cost over $1 billion in 1930’s dollars, federal relief programs.

• US was better prepared for a longer drought in 1950s.

Sea Surface Temperature Anomaly 1932-1939

OBSERVED

Contour interval = 0.2°C

A cold, La Nina-like, tropical Pacific Ocean

The Dust Bowl Precipitation Anomaly (1932-1939)

GOGA MODEL

GOGA MODEL = Global Sea Surface Temperature Specified

Contour interval = 2 mm/month

OBSERVED

What about BEFORE the instrumental record?

Tree ring evidence for drought

Thickness of tree rings in some species is sensitive to rainfall.

Narrow band = dry climate

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LONG-TERM CHANGES IN DROUGHT AREA IN THE 'WEST'

THE CENTRAL DATES OF THESIGNIFICANT (p<0.05) EPOCHSARE INDICATED WITH ARROWS

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Cook et al., Science(2004)

A Longer Perspective on Drought:Tree Ring Reconstructions

Past droughts have been longer and more severe

Medieval Droughts

Similar pattern as modern drought.

Conditions persisted MUCH longer (20-40yrs)

‘Mega-droughts’

40 years

30 years

25 years

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Drought and the Anasazi (ancestral Pueblo)

Classic example of cultural impacts of climate change.

Studies of the Four Corners region show population crashes related to megadroughts

Benson et al. (2006)

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Anasazi depopulation of the SW US

The “Great Drought” spanned 1272-1298 AD (~26 years).

Other factors: Warfare, balkanization, religion.

Mesa Verde, CO

Interannual-Decadal Variability

– Severe droughts lasting decades are common (many per millennium).

– This mode of climate variability is present in the instrumental record (that is, expected).

– Cultures can and do readily adapt to these variations.

Is this the full range of natural climate variability at socially-relevant timescales?

Holocene Climate

The Holocene represents the present warm period (last ca. 12,000 years).

It’s “Our Time”, spanning the emergence of agriculture and civilizations.

– How stable was it?– What factors influenced Holocene climate

change?

Mechanisms of Holocene Climate Change

– Long-term: Earth orbital variations (millennia)– Shorter-term: Solar variability, volcanic eruptions

and greenhouse gases (century-scale)

– Ocean-atmosphere interactions (El-Niño, NAO…)– Natural, unforced variability (random)

Stable or Unstable Holocene?

Unstable! Persistent 1500±500 year variability

The Little Ice Age and Medieval Warm Period were the most recent of these events...

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Greenland Temp. (°C)

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Bermuda Rise SST(°C)

West African SST(°C, anomaly)

Age (yr BP)

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Medieval Warm Period

Mid-Neoglacial

Little Ice Agea

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Most of the variability over the past 1000 years due to solar variability and volcanism.

Cultural Responses to Holocene Climate Change

• Paleoclimate records document large climate changes which persisted for many centuries to millennia.

• Climate transitions can be very abrupt.• Regional to global (?) extent.

• What impact did these climate perturbations have on complex societies living at the time?

• Examples:– Akkadian Empire (ca. 4200 yrs BP)– Classic Maya Empire (ca. 1200 yrs BP)

Akkadian Imperial Collapse (4200 yrs BP)

• First empire imperialized Mesopotamia between 4300-4200 yr BP.

• Imperialization linked productive rainfed (semiarid) agriculture of northern Mesopotamia (Sumer) with south.

• Collapse occurred near 4170±150 yr BP (Weiss et al., 1993).

• Collapse was previously attributed to political disintegration.

Sargon of Akkad

Tell Leilan, NE Syria

• Weiss et al. (1993) excavated this former Akkadian imperial town.

• Their results suggested rapid abandonment due to onset of aridity.

• At right, a ~600m2 excavated residential occupation with roadway.

Deep-Sea Sediment Record of Mesopotamian Climate

Cullen et al. (2000) tested the Weiss et al. (1993) claim using the deep-sea sediment record to reconstruct changes in Mesopotamian climate.

– Late Holocene aridity record should be preserved in deep-sea sediments.

Euphrates

Tigris

Nile

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Dust source areas Summer surface winds &dust transport vectors

M5-422

Tell Leilan

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Mesopotamian Dust

Dust storm over Mesopotamia (May, 2000)

Same dust storm, 10 days later, over the Gulf of Oman

Climate Change and Akkadian Collapse

Cullen et al. (2000)

Akkadian Collapse

• Onset of ~300 year period of greatly increased aridity near 4025±125 yr BP coincides with Akkadian collapse at 4170±150 yr BP (within dating uncertainty). – How widespread was the collapse?

• Enhanced aridity at this time also reported for Turkey, Israel, and Egypt.

• Nd and Sr isotopes confirm dust is from a Mesopotamian source similar to Tell Leilan.

• Volcanic glass shards found at Tell Leilan and in the deep-sea are geochemically correlative.

Classic Maya Culture (300-900 AD)

Classic Maya culture ruled Mesoamerica from 250 to 850 AD.

Late Classic culture (550-850 AD) known for highly stratified society, vast trade networks, and widespread construction of urban centers and monumental stellae.

8-15 million people across Yucatan Peninsula

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Tikal (Guatemala)

Classic Maya Collapse (800 AD)

Classic Maya empire collapsed at peak intellectual and cultural development at 900 AD.

Lowland urban abandonment

End of monument construction

Cultural disintegration

Factors cited: Deforestation, overpopulation, warfare, religious and social upheaval.

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Largest urban center: Palenque

Cariaco Basin (Venezuela)

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Annual laminations

Cariaco Basin laminated sediments

Mayan collapse occurred during a 150-year drought!

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Climate Change and Classic Maya

Collapse

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What can be learned from these examples?

Complex societies are sensitive to climate change.

Paleoclimate records document changes in climate which surpassed modern variability.

Other social factors in each case may have contributed to observed collapse.

Collapse occurred despite evidence that these cultures had large buffering capacities.

Conclusions

Modern and ancient cultures:- Thrive in marginal environments.- Plan for the future based on recent past (regrettably)- Learn and adapt (fortunately).

Only ancient cultures experienced century-scale drought.

Their past can be a guide to our future.

Lessons from the past

Complex societies are both adaptive and vulnerable to climate change.

Past climate changes far surpassed modern variability.

Collapse occurred despite large buffering capacities.

ModernLake Powell

2002

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Lake Powell levels, today