Transcript Cultural Responses to Climate Change: Lessons from the

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):
–
–
–
–
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Glaciers
tree rings
corals
lake and ocean sediments
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Tree-ring record of drought
in the American SW
wet
dry
The 1930s Dust Bowl
• Six year drought (19331938), well-documented.
• Due to wanton farming
practices and overcapitalization.
• 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)
OBSERVED
Contour interval = 2 mm/month
GOGA MODEL
GOGA MODEL = Global Sea
Surface Temperature Specified
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
A Longer Perspective on Drought:
Tree Ring Reconstructions
Past droughts have been longer and more severe
LONG-TERM CHANGES IN DROUGHT AREA IN THE 'WEST'
% DROUGHT AREA
100
THE CENTRAL DATES OF THE
SIGNIFICANT (p<0.05) EPOCHS
ARE INDICATED WITH ARROWS
1150 1253
936 1034
80
60
40
DRIER
20
0
WETTER
800
1321
1613
1829
1915
900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000
Cook et al., Science
(2004)
YEAR
30 years
Medieval Droughts
Similar pattern as modern
drought.
40 years
Conditions persisted MUCH
longer (20-40yrs)
25 years
22 years
‘Mega-droughts’
Drought and the Anasazi (ancestral Pueblo)
Number of habitation sites
Classic example of cultural
impacts of climate change.
Studies of the Four Corners
region show population crashes
related to megadroughts
Benson et al. (2006)
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...
Greenland Temp.
(°C)
0
500
Age
1000
(yr BP)
1500
2000
-32.0
-31.0
Bermuda Rise SST
(°C)
21
22
23
24
25
West African SST
(°C, anomaly)
-6
-4
-2
0
2
a
Little Ice Age
b
Medieval Warm Period
Mid-Neoglacial
2500
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
40
50
60
40
Tell Leilan
Eu
ph
ra
tes
30
M5-422
20
– Late Holocene aridity record
should be preserved in
deep-sea sediments.
Nile
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30
ris
Tig
Cullen et al. (2000) tested the
Weiss et al. (1993) claim
using the deep-sea sediment
record to reconstruct
changes in Mesopotamian
climate.
10
Dust source areas
Dr. Heidi Cullen
The Weather Channel !
Summer surface w inds &
dust transport vectors
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.
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8-15 million people across Yucatan
Peninsula
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
Climate Change
and Classic Maya
Collapse
Cariaco Basin
laminated sediments
Mayan collapse
occurred during a
150-year drought!
wet
dry
0
1
2
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.
2002
Modern
Lake Powell
2003
Lake Powell levels, today