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Cultural Responses to Climate Change: Lessons from the Holocene Peter de. Menocal (Lamont-Doherty Earth Observatory of Columbia University)
Climate - Society Theories “Cultural Determinism” – Culture alone determines culture. – Prevalent throughout 18 th-19 th 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
Tree-ring record of drought in the American SW wet dry
The 1930 s 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 1950 s.
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 = 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 Cook et al. , Science (2004)
30 years Medieval Droughts Similar pattern as modern drought. 40 years Conditions persisted MUCH longer (20 -40 yrs) 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. . . 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 ~600 m 2 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. Dr. Heidi Cullen The Weather Channel !
Mesopotamian 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 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. Largest urban center: Palenque
Cariaco Basin (Venezuela) 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