Lecture 5: Ancient impacts of people on climate change Flashcards
Anthropocene: Human impacts push the Earth system (particularly ___ system) beyond its
climate system
natural range of variation
when did the anthropocene begin?
DEBATE
- pre-industrial? (fire & hunting, origins of agriculture)
- industrial ? (industrial revolution, nuclear age?)
holocene
last 10,000 years
Industrial effects are obvious (CO2 + Methane)
Huge ‘hockey stick’ curves showing increase following industrial revolution
earliest impacts of humans on the planet (4 points)
1) hunters and the megafaunal extinction
2) deglaciation & origins of agriculture
3) pre-industrial spread of agriculture
4) Climatic impacts of early agriculture
Hunters & megafaunal extinction
- loss of wooly mammals etc
- on every continent (Johnson 2009)
- big animals more bias (more threatened)
- small animals thriving in modern world
- population sizes smaller in large animals, slower growth rates, breeding slower = more vulnerable to extinction
causes of megafaunal extinction?
debate, extinction correlated with human arrival
Johnson 2009
Agriculture: began? where? what does it allow?
- 10-12 thousand years ago
- began in multiple independent regions across the world
- allows society to support high no. of people in one place
- allows people to have diff jobs in society (farmers, not farmers, tax collectors)
modern agriculture
- industrialised
- support cities (importation)
- free from need to go out and work and collect (hunter & gatherer)
- tech innovations stem from agriculture (people have time on their hands)
hypothesis into why agriculture began?
- DEBATABLE –> lots of hypothesis
- - i.e. local resource availability, population growth, tech innovation, dietary breadth etc
hunter gatherers ate …
- were farming!
- a broad spectrum of wild grains
- Ohalo II, 10,000years BEFORE agriculture
- tool use (weapons, grindstones)
- wheat, barley & other things
transition to agriculture involved specialisation from a large pool of wild species
to a few crops
- wheat, barley, pulses etc
deglaciation probably allowed __ to begin
agriculture
Was agriculture impossible during the glacial?
YES,
-necessary tech & intellect:
low & unpredictable plant productivity made it impossible to specialise on a narrow range of crops
- picking a few crops = runs risk of high crop loss
- so they go out, collect things in season, buffers you to environmental change
domestication of crops allowed
- greater yields
wild crops disperse their own seeds - domesticated dont
– they rely on us, we do them
agriculture began & spread =
fertile crescent (iraq, iran, israel etc) and then spread through Europe and England in 5000 year ago - agriculture spread from where it began
agriculture spread meant the __ of trees
deforestation
from beginning agriculture (10,000) to now. Has tech innovations changed per capita land-use?
- productivity of crops has improved,
- shrinking per capita land-use
- land change occurred further back in time
- early anthropogenic view supports pre-industrial deforestation
technological innovations in food production
- hunter-gatherer management of landscapes by fire
- food processing methods
- cultivation of sown seeds in intensive gardens
- agricultural economies (manuring, ploughing)
- irrigation, multiple cropping, rotations, fertilisers,
- industrial evolution
- green revolution
Ellis et al 2013
indirect climatic impacts of pre-industrial agriculture
comparison of CO2 & CH4 in current interglacial (holocene) and past (eemian)
- Now in holocene, increase in CO2 and CH4 (slightly more recently)
reasons for CO2 and CH4 holocene interglacial levels
- CH4 emissions from paddy rice & livestock
- CO2 emission from deforestation for agriculture
- RUDDIMAN 2013
- – debatable though!
- prior to 3000 years ago, only half CO2 was from deforestation
- CH4 nature variation explains CH4 conc changes