week 11 summary Flashcards
What has played a key role in human evolution
and migration?
climate
What is the Savannah hypothesis?
drying trend in Africa
Tropical rainforest transitioned to grassland savannah
human Ancestors forced onto the ground,
encouraging bipedalism, rapid movement and resourcefulness
What is the Variable selection hypothesis?
Rapid climate changes , favouring those who had traits that were useful to surviving in an increasingly challenging environment
Humans as ‘master invaders’
What is the Pulsed climate hypothesis
Hominin expansion and diversification associated with
orbitally driven climate pulses
Stepwise expansion in brain size 1.9 Ma coeval with
occurrence of ephemeral lakes in the Rift valley
What might have facilitated the development of agriculture?
the more stable Holocene environment
What has climate change likely contributed to in the past?
Climate change has likely contributed to the
collapse of civilisations in the past
What is the Early Anthropogenic Hypothesis?
Humans actions have significantly impacted the climate and environment long before the industrial revolution
What trends are different in the holocene when compared to other interglacials?
CH4 and CO2 are anomalous
What caused the rise in CH4 ~5,000 years ago?
rice irrigation and tending
livestock
What caused the rise in CO2 ~7,000 years ago?
deforestation and burning
When do humans begin to be active contributors to the climate system?
10,000 to 8,000 years ago
What had happened by 3000 years ago?
Hunter gatherers, farmers and pastoralists had transformed the planet
What is the key driver over human systems?
Climate variability over interannual to decadal time
scales
What are the key drivers of year to year climate variability?
ENSO, IOD and SAM
When have ENSO, IOD and SAM changesed?
over the last 50 years
What paleoclimate archives are used to measure decadal variability?
High resolution palaeoclimate records, such as tree rings, speleothems, corals and lake records
How often does ENSo occur?
every 3- 8 years
What does ENSO control
driver of rainfall and temperature variability particularly over eastern Australia
What is indies is ENSO measured through?
- sea surface temperature
- sea surface pressure between Tahiti and Darwin
What are the key theories relating to human evolution and climate change?
- Savannah hypothesis
- Variable response hypothesis
- Pulsed climate variability hypothesis
When is the greatest increase in brain size linked to?
Variable selection hypothesis
period to greatest climate variability
How may the younger dryas have enabled expansion in agriculture?
- Intensification of dry conditions in Eastern Mediterranean
- People gathered near dependable water sources
- Wild grains accidently germinated nearby
- So began cultivation of crops
What are examples of human civilisations being negatively affected by climate?
Egyptian dynasties-Weakening of monsoon 5,000-
6,000 yr ago
Akkadian (Syria)-Abrupt abandonment of villages with increased aridity ~4,200 yr ago
Maya civilisation- collapse of lowland Maya civilisation ~800 – 1000CE
• Evidence of a 20- 60% reduction in rainfall
When did CO2 diverge in mid holocene?
~7,000 years ago
• released due to deforestation,
burning
