Climate and ancient civilizations

how was climate change traditionally viewed before a few decades ago

As gradual, occurring over centuries or millennia, barely perceptible during a human lifetime.

What has recent evidence shown about climate change in the Holocene?

Climate can change abruptly — large shifts (several °C) can occur in decades or even years.

What are Dansgaard-Oeschger (D-O) events?

Abrupt cooling oscillations superimposed on the Holocene trends, with notable events at 8.2 ka, 5.5 ka, 4 ka, and 1200–1650 CE.

What happened during the 8.2 ka event

• Abrupt cooling and drying lasting ~200 years

• Seen in GISP2 Greenland ice cores

• Widespread arid conditions from North Africa to Asia, also parts of Americas & NW Europe

What was the 5,500-year event?

• Abrupt shift in precipitation (~5.5–5.3 ka)

• Transition to drier conditions in NW Africa (end of African Humid Period)

• Linked to decline of Elm in Europe and Hemlock in North America

• Associated with abandonment of Skara Brae (Orkney Islands)

what was the 4,000 year event

• Strong cold and arid event in North Atlantic, North Africa, and southern Asia

• Coincided with collapse of major civilizations: Old Kingdom Egypt, Akkadian Empire, Indus Valley, Early Bronze Age societies in Anatolia/Greece/Israel, Hilmand civilization, Hongshan culture

what is the little ice age

• Most recent Holocene cold event (~1200–1850 AD)

• Two periods:

  1. Medieval Cold Period (MCP/LIA b): gradual start ~1200 AD, ended ~1650 AD, affected Norse colonies and caused famine in Europe

  2. Classical LIA (LIA a): most rapid & largest change in North Atlantic, Greenland ↓0.5–1°C, West Africa SST ↓4°C, Bermuda Rise SST ↓2°C

• Impacted civilizations in Central & South America, including the Mayan collapse

what is significant about skara brae (orkney islands)

Neolithic sandstone houses, buried in sand until 1800s storms exposed them; dated ~5,000 years ago; bone-beaded necklaces found; abandoned due to cold Holocene climate events.

• climate cycles affect settlement, region = sig cooling in 5.5 ka likely causing abandonment

old kingdom of egpt 220 bce

(2700–2200 BCE)

prior stable conditions: Fertile Nile valley, natural desert barriers, monumental architecture like the pyramids.

collapse caused y 200 year period of arid climate

egypt split into north+ south, sediment shows drier conditions and ice rafted debris

recovery from 2050bc onwards in middle kingdom

Was climate a cause of Rome’s fall?

Tree-ring data shows cooling during collapse; but political pressures from migrating Germanic and Mongolian tribes were primary causes.

What natural factors contributed to the Mayan collapse 900 CE?

Drought, soil exhaustion, water loss, hurricanes, earthquakes, climate change.

human factors however icl. peasant revolts, warfare

major drought triggered urban system collapse

impacts of the little ice age

Thames River froze; famine in Europe (~1 million deaths); collapse of Norse colonies in Greenland; influenced Mayan, Inca, Aztec societies indirectly.

: Great Famine, Thirty Years’ War (1618–1648), shifts in food production.

How did the Columbian exchange affect climate?

Massive depopulation (~56 million in Americas) → land abandonment → CO2 drop → regrowth of forests → temporary global cooling (0.2–0.3°C), coinciding with the LIA.

How was the Ming Dynasty affected by climate?

Collapse occurred during the LIA, 1600s ; climate stress (cooling, drought) likely contributed to societal strain.

What patterns of climate change occurred in the Holocene?

Threshold events(Climate can change gradually, but once it reaches a certain tipping point, it can shift suddenly and dramatically), cycles (~1.5kyr climate tends to repeat patterns), and one-off abrupt events; climate was not entirely stable.