natural & anthropogenic changes Flashcards
what is earth temp regulated by
balance between how much energy comes in the system (sun) + how much goes out
what is Heat absorbed by the Earth re-emitted as
longwave radiation (IR)
what is the heat entering the system
the light that hits top of atmos and gets absorbed – some gets reflected and scattered away by tiny particles (droplets, dust etc)
what 3 things is More long-wave radiation absorbed by
- CO2
- water vapour (clouds) - good at absorbing light
- nitrous oxides
**all associated with climate change
what is insolation
Radiation reaching surface
what is albedo
insolation reflected by surface
Snow: high albedo, Soil: low albedo
what happens to Radiation that’s reflected back off surface
absorbed in the atmosphere (Atmosphere: blanket keeping heat in)
- This reflected radiation is usually infrared & longer wavelengths
- H2O vapour & CO2 strongly absorb infrared
what is CO2 accelerated by recently
- Greater industry activity: burning fossil fuels
- Deforestation & land clearance
some stats about increase in global temp
- From 1959-2011: 24% increase in atmos CO2
- Between 1906-2005: Mean global surface temp increased 0.74oC
- Proportion of sea ice has decreased around 1/3 - less albedo + reflection of light – gets absorbed by sea instead
where takes direct measures of [CO2]
Mauna Loa Observatory, Hawaii
what’s used to take samples of CO2 concentration years ago
ice cores, coral drilling + tree rings
what conditions can we see in High-mid latitudes + Low latitude
- High-mid latitudes = cold: glacials (ice ages) & interglacials
- Low latitude = warmer: interpluvials (dry) & pluvials (wet)
name Milankovitch’s 3 astronomical cycles
- axial tilt
- Eccentricity of the Orbit
- Precession of the Equinoxes
what does Milankovitch’s 3 astronomical cycles explain
the drives of glacial cycles - cycles between warm & cold periods
- 3 factors that control sunshine reaching high N latitudes: ~20% light variation
what does the axial tilt explain
- Tilt of Earth’s spin – what causes seasons
- ~21.5o to ~24.5o and back every 42k years
- More intense/defined seasons in both hemispheres – bigger tilt
what does Eccentricity of the Orbit explain
- Orbit circular, elliptical & back ~100k years
- If jupiter + saturn are to one side and pulling in the same direction it elongates that orbit to one side
- Weaker effect on seasonality than axial tilt
- Intensifies seasons in one hemisphere + Moderates seasons in the other hemisphere
what does Precession of the Equinoxes explain
- Wobble of spin axis + effect of tidal pull of moon and sun on the earth - causes planet to slightly wobble
- Interplay between the 1st two factors
- Increases or decreases the tilt of the planet – intensifies or weakens seasonal variation
what’s the problem with believing Milankovitch’s 3 astronomical cycles
No independent record of ice age timing – need to try get this from the sea
what allows us to track what’s going on in terms of temperature
Ratios in O2 isoptopes (O16, O18)
why do we use O2 isoptopes to track temperature
- Tend to have < O18 in ice than normal water
- 18O/16O in SW tracks ice volume on land
- H2O vapor: 18O precipitates more readily than 16O
- 18O evaporated from ocean less likely to travel from source than 16O
- Oceans enriched with 18O during glacials
how can we use O2 isoptopes to track what’s going on in terms of temperature / ice ages
- Foraminifera use 18O/16O for their CaCO3 tests (shells)
- Die, sink, bury O signature in sediments
- Record of 18O/16O from forams in deep-sea cores:
- Ratio fell & rose in accordance with Milankovitch cycles
- Found Ice volume peaked every 100K yrs: eccen of orbit
- Other 2 cycles (23Ky & 41Ky): wrinkles
- Shows temp is varying because of these cycles
how can we link temp with atmospheric CO2
- Analysed CO2 in ice core bubbles from Antarctica & - Greenland – looks at ratio of CO2 : N + O2 in the air bubbles on the ice
- V good correlation between CO2 & temp
- Low temp: result of low CO2
how can we Link temp with ocean CO2
- Oceans regulate atmospheric CO2
- Ocean can act as large CO2 sink & hold 50-60 times more CO2 than the atmosphere
- Oceans = powerful CO2 pump - more efficient during glacial periods
how does ocean control the global climate
great ocean conveyer belt
- Warm water gets drawn from gulf of mexico, over the north atlantic to northern europe – that heat gets released into atmosphere
- NADW floods deep Atlantic, distributes around other oceans
what might drive the earth to further increase in atmos CO2
- Milankovitch Cycles major driving force – but happens in long periods
- Human perturbation = big consequence – rapid and severe changes in system
- However: Gradual changes in external forcing lead to ABRUPT & SEVERE alterations in climate
what are the evidence that the rise in atmos CO2 could flip climate
- Over past five decades: increased freshening of Nordic seas – melting sea ice, increased rainfall
- Leads to Slowed NADW formation that drives the thermohaline conveyer
- Overflow decreased 20% since 1950
- Future: worsen with increase in CO2 + temp
- Accelerated melting of Greenland ice sheet
- Continued freshening: collapse of Atlantic Thermohaline Circulation?
- Models suggest 45% collapse by 2100 if CO2 emissions not cut
- Rapid cooling of NW Europe ??
2 reasons ~30% anthro CO2 taken up by oceans
1) Increased atmos CO2
2) Increased PP & organic sedimentation
