Ancient Climate/Environmental Change

Climate Proxies

Natural record of past climates!

1. Dendrochronology + Glaciation + Dinoflagellates: reconstructs temperature (Roman warm period is good for dating, Late Antique Little Ice Age is not)

   1. Dinoflagellates are algae on ocean surfaces + different species prefer different conditions/nutrients → their shells sink to the ocean floor when they die + record

2. Sedimentation stratigraphies + Stalactites (Speleothems): oxygen + carbon measured from plants to match this (thus need to know a lot about plants/environment as well) + need to still be growing

3. Ice cores: measure sulfur from volcanic eruptions, Beryllium 10 for solar

4. Modern climate modeling

5. Paleogenomics: study of ancient DNA or aDNA for migration studies + epidemics

6. Viticulture in the Levant and Italy, or wheat production in Egypt and North Africa + expansion of these industries

   1. could also be due to human ingenuity

7. Solar Activity through…

   1. Milankovitch cycles: orbital tilt, very long change i.e. glacial time scale

   2. 11 year cycle: short term change in the sun’s magnetic activity

What are the 3 cells in Atmospheric Circulation

Hadley Cells, Westerlies, and Polar Cells

What are Hadley Cells

Right above + below the ITCZ, caused by trade wind circulation patterns

What is the Intertropical Convergence Zone? How does it move/impact the Earth?

Trade winds converge at the equator - moves and creates shifts in climate

1. Goes along with tilt of the Earth; as it rotates the ITCZ moves throughout the year

   1. Earth’s orbit has generally shifted over time

2. Impacts the Indian ocean monsoon, pushing it south, making Egypt drier (key idea: climate patterns can impact any region on the planet)

3. Winds preventing the monsoon from going where it wants to, over long time scales it has shifted (i.e. glacial timescales)

How does atmospheric circulation influence climate?

• Warm air sinks = desert, cold air rises = releases rain

• Atmospheric (and ocean) circulation help distribute the sun’s energy across the Earth

Seasonal temperature changes caused by…

Earth’s tilt changes the angle of sunlight/length of day

Global Water Cycle

Movement of Water between atmosphere, ocean, and land

• The hydrologic cycle is a major component of energy balance

• Condensation releases heat in the atmosphere

• Western ocean sends warm water to the poles

• Eastern ocean sends cold water to the equator

Atlantic meridional overturning circulation (AMOC)

• Keeps ocean temperatures/weather patterns in specific regions consistent, but impacts long term global climate 

  • Specifically in the North Atlantic Ocean near Europe

• Influences North Atlantic Oscillation, which influences…

  • the Mediterranean indirectly through El Niño

  • the Nile indirectly through Indian Ocean Monsoons

Thermohaline Circulation

Deep water current meets with other currents and upwell + change

• happens on a much larger time scale than seasonal changes

• crucial for long term climate because it stores heat and carbon

• Greenland ice sheet melting could stop this flow, which would cause the Northern Hemisphere to go into an ice age

Benefit of stable climate in antiquity

Stable food source!

What was the LALIA triggered by?

3 massive eruptions

• 536, 540, and 547 CE

Caused climactic cooling → shifting environments → trophic cascade collapse → rise in lower scale species (i.e. rodents)

• also see people migrating

Hittite Collapse

1200 BCE, around the Late Bronze Age Collapse

• Dendrochronology as a proxy for rainfall

  • aligns with speleothem records in Turkiyë

  • Anatolian records show 3 year drought episode coincide with this collapse

Okmok Eruption

43 BCE

• Triggered by extreme global climactic downturn

• Coincides with Roman and Ptolemaic collapses

• Tephra ash found in Greenland ice cores (tephra doesn’t usually travel far = HUGE eruption)

Sources showing serious environmental stress

• Cassius Dio: sun blocked out, sun dogs (i.e. refractions of sunlight via minerals in ash)

• Plutarch + Appian: food production slows

More than just an eruption

• Suppression of the Nile flood → revolts + political instability

• Ptolemaic papyri records: strong correlation between state decrees, agriculture, war, economic stress, and social unrest

Fayum, Egypt Collapse

Rivers are carved from the Nile so water can collect in the Fayum Depression

• Trade winds shift = no more monsoon = drier Egypt

Evidence of previous water collection

• Nileometers: measure flood size

• Qanats: shafts → tunnels → mother wells that extend the aquifer

  • North Qarun Oasis

Post Roman Climate Optimum

2nd-7th ce

• many abandoned cities on the Nile delta as flooding becomes erratic

Sites

• Kharga: digging/altering more qanats = struggle to sustain water table = water shortage

  • shift from agricultural production to fortress/stopping points along trade routes - wells found inside fortresses = water was precious