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Week 11 - Earths System Dynamics and Intersystem Interaction; the Last 2…
Week 11 - Earths System Dynamics and Intersystem Interaction; the Last 2 Million Years
CAUSES OF ENVIRONMENTAL CHANGE - tectonics (long time periods) climate (multiple time periods) humans (increasingly in recent millennia)
HUMAN INFLUENCE - humans may have deliberately lit major fires in tropical savannahs for 1000s years
agriculture for 4k years
impacts of ghg emissions since 19th century substantial in c20th and c21st, affects global climate, not just local environments
CLIMATE CHANGE - until recent centuries/millennia, major observable environmental changes on earth caused by natural climate change.
Climate change affects: temperature, precipitation and atmospheric circulation
WHICH FACTORS FORCE GLOBAL CLIMATE CHANGE? - variations in solar output, volcanoes, solar system transparency variations, anthropogenic greenhouse gas emissions, earths orbital variability
ORBITAL THEORY - James Croll 19th century Scottish inn keeper, amateur astronomer, recognised earths obit not constant through time.
Milankovitch, Serbian mathematician, calculated dynamics of earths orbital variability
DIMENSIONS OF ORBITAL THEORY - shape of orbit (eccentricity) circular elliptical: 94k yr cycle
Tilt of axis (obliquity) 21.5-25º variation: 42k yr cycle
Wobble of axis causes equinox precession 21k yr cycle
HOW DOES IT ADD UP? -
Key is probably how the 3 factors interact
Milankovitch & others have calc cumulative radiation effects
Need corroborative evidence of impacts from earth systems, as systems contain complex responses & feedbacks too
CLIMATE FEEDBACKS
e.g. cooling:
< radiation receipt (orbital effect)
Cooler atmosphere and oceans
More snow accumulation, ice growth
Draw-down of CO2 from atmos: more soluble in cold water
< veg growth (link to temp & CO2 ↓ )
less CO2 = less greenhouse effect (also methane declines)
enhanced cooling, etc
ANTHROPOGENIC GLOBAL WARMING - Human activities have raised atmospheric CO2 (and other greenhouse gas) concentration(s) from ~280 ppmv (natural background interglacial level) to ~417 ppmv since 1750.
This has very likely contributed to ~1.1degC Global Warming since 1900.
Arctic already showing clear signs of major change (ice melt) over past few decades: very likely due to ice- albedo & other +ve feedbacks.
Climate models predict likely 1.0-5.7degC global warming compared to 1850-1900 average, and 0.28- 1.01 m global sea-level rise by 2100 compared with 1995-2014 (IPCC AR6 WG1 2021)
WHAT IS GAIA? The Earth, its rocks, oceans, and atmosphere, and all living things are part of one great organism, evolving [and self-regulating] over the vast span of geological time.” (Lovelock 1988
GEOPHYSIOLOGY - are climate and chemistry related?
Organisms & material environment evolve tightly coupled together
Feedbacks between growth, constrained by life’s preferences, and environmental change. → self-regulation by Darwinian natural selection, e.g. Daisyworld (model simulation).
Lovelock proposes that Earth actively keeps climate & chemistry always comfortable for its inhabitants.
CRITIQUE OF GAIA - Life on Earth affects climate but not necessarily for the better.
Humans are a prime example in blindingly following our own self-interest: e.g. anthropogenic global warming may have deleterious effects for many other sensitive species less able to adjust, e.g. coral reef communities.
Yet according to Gaia theory, we are naturally appointed custodians of planet Earth and have a duty to protect a planet potentially highly sensitive to climatic perturbation.