Anthro Flashcards
(29 cards)
When could the anthropocene have begun?
1610
1950
4000 ya
What forces are responsible for past CC (big)
Null model - what would happen without humans. Natural processes can affect climate too
Plate tectonics - results in configurations of land masses and oceans that affect the Earth’s climate
- continents at polar regions accumulate snow and ice = incr albedo
- enclosed seas and oceans at poles reduce heat exchange with other oceans, cold polar regions have sea ice, glaciation of continent rim, again incr albedo (fraction of short wave radiation from the sun reflected from the earth back to space)
- continent and ocean configuration can also affect currents that are crucial for energy transfer around the globe.
- plate tectonics can result in mountain ranges that modulate continental and regional scale climates. Mountains also incr albedo, incr weathering (dissolving and reduction of CO2), and N/s mountain ranges disrupt E/W circulation
Milankovitch cycles- eccentricity (shape around the sun), precession (wobbling axis), obliquity (tilt of axis)
How can we measure climate change in the past?
O18 variation can be seen in Benthic foraminifera
Tertiary sediments eg Greece show alternating brown and white layers reflecting the climate at the time they were laid.
Brown (lignite, brown coal) set down in drier periods, swamp veg
White (marl, calcium rich mudstone) wetter intervals, lake
Precession affects rainfall at mid to lower latitudes. Each couplet of white and brown shows one precession cycle. Variation within couplets shows sub-milankovitch climatic fluctuations. Couplets contrast is modulated by eccentricity
Methane concentrations in ice cores vary in near synchrony with precession pattern and solar radiation (until recently- see peak where solar radiation falls
CO2 concentrations in ice cores. Varies with precession but looks odd in very recent history (human actions).
- Exact cause not fully understood but thought to involve effects of M cycles on growth and decomposition of veg in N hemisphere
Minima of solar radiation, more glaciation, less veg, so less CO2 and methane produced by decomposition –> theory
CH4 and Co2 diverging from patterns, long before great acceleration affecting GG, before history –> earlier start to anthropocene?
Climatic variations at smaller time scales are caused by?
Ocean Thermohaline Circulation
Fluctuations in Solar energy eg rivers
Oscillators eg La Niña
Volcanic eruptions
Key impacts of climate change
- Ecosystem function and spp composition
- Rainfall changes
- Large scale changes in vegetation cover may feedback to regional rainfall patterns eg savannah
- CO2 fertilisation and warming effect of rising atmospheric CO2
- Above ground C stocks in Savannah are strongly contingent upon disturbance regimes
- Fires
- Ocean acidification
How to experiment climate change
- Eddie flux towers to look at the transfer of gasses- determines exchange rate of trace gases to quantify gas emission rate
- Warm plot with infrared lamps
- Soil heating cables to warm soil
- Covers that can move over a plot when ppt is sensed
- Chambers that have altered CO2 and temp levels - small scale
- Branch bags
- Phenocam can look at the landscape and see how much green/brown so can understand when senescence is occurring + remote
- sonic anemometer- uses ultrasound as air packets move through) measures phot and respiration in dark
- Pumping liquid CO2 to gas to increase co2 to twice the normal ambient level- eg duke forest co2 enrichment experiment
How can we determine migration patterns?
Radio telemetry Colour marking Satellite tracking Genetic and isotope studies Geolocators
How do birds prepare for migration
- Moult all of their flight feathers
- Build up flight muscles- premigratory hypertrophy. Eat like crazy particular types of food high in certain nutrients so can put on lots of muscle mass
- Changes in Basal Metabolic Rate promotes high food intake. Especially artic breeders
- Changes in diet and eating behaviour- many switch to frugivory bc higher calories from insectivory
How might climate change affect migration
Phenological mismatch
Weather can affect species ability to migrate (eg where they can stop for food/ favourable wind currents)
Wy do we think anthropocene began in 1950
‘The Great Acceleration’
Big uptick in: Population GDP Fertiliser consumption Urban populations Large dams Water use Paper production transportation telecommunications foreign direct investment
Earth system trends also experienced an uptick: Co2 NOx Methane Surface temp Ocean acidification Marine fish capture Shrimp aquaculture Tropical forest loss Domestic land Terrestrial biosphere degradation
Also have stratigraphic signatures: technofossils C N P deposition Co2 CH4 CC and sea level rise Extinctions Nuclear weapon fall out
Technofossils
Plastic- can fall to the bottom of the ocean to the benthos and remain in sediment. Could be found in many years (100s). Photo-degradation also leads to a range of plastic particle sizes including micro plastics.
Aluminium- 98% of production since 1950
Concrete- invented by the romans so been around for a while
Mineral extraction and sediment- ME accounts fo 57,000 Tgyr-1 of sediment displacement= 9,500 great pyramids of giza. We move these materials around for industry. In the UK 50Tgyr-1 of material moved by rivers, 688Tgyr-1 by us.
Carbon- Spheroidal Carbonaceous Particles (SCP) and black carbon (soot) has been increasing since the industrial revolution. Increase accelerated in 1950 on globally near synchronous. SCPs will remain in sediment
CO2 and CC
Increase in CO2 in late Pleistocene, gradual increase through holocene, Rise in C13 mid holocene. Preferential C12 uptake in biosphere; ocean release.
A lot of C burned in industrial revolution so now lots of C12 from fossil fuels and relatively less C13. Isotopic ratios will be picked up in geological records.
Overall cooling trend in last 2000 years but we have this uptick. Temps in southern hemisphere and tropics already exceeded holocene variation. N hemisphere following suit.
Biotic exchange and homogenisation
Eu and N america have been separated for a long time, so they have evolved distinct biotic But moving species around the world you homogenise biota by mixing them and losing differentiation
eg st helena
Island . Used to be vegetated. portuguese introduced goats and other mammals so they’d have food when they came back. Goats consumed so much vegetation over time soil and vegetation washed into sea. Humans also introduced novel plants. Novel communities. These species will leave their pollen and bones in sediment in places where they did not evolve.
Fall out radionuclides from weapons
Global synchronous appearance of radionuclides give Global Standard Stratigraphic Age (GSSA). Peak in radioactive plutonium and carbon (C14) in 1964 following peak in nuclear weapons testing.
The start of anthropocene highly contesting. Some say 4000 years ago when farmers started changing the surface of the land (most of the worlds forests were converted to cropland and cleared before 1950). Some argue agriculture was the revolution that allowed humans to develop.
To define an epoch the International’s Commission on Stratigraphy accepts layers of any sedimentary material- ice core, tree rings, stalagmites. But some argue none have been found for the anthropocene.
Some contest that holocene because glaciations have been happening cyclically and pretty consistently over the last 2.8 MY. This one happens to get a special name because we live in it. Some believe CC may have broken the cycle of glaciations so we defo need a new name if that is the case.
Why does the new epoch matter for ecology
1700: 50% land surface wild, 5% intensively used
2000: 25% wild, 55% intensively used
Transformation of biomes from natural to anthropogenic. Currently remaining wilderness is 22%, most of it in 20 countries. At all scales have to study organisms with consideration of humans. Humans are major ecosystem engineers, destruction, transformation and restoration, novel ecosystems. Setting specie on novel evolutionary trajectories
Ocean thermohaline circulation and smaller variations in earths climate
Driven by gradients in ocean temp and salinity, affecting sea water density. Cold, dense, salty water sinks low.
North Atlantic Deep Water (NADW) formation makes way down to south pole then upwells at some point and becomes warm again. Thought (at least in part) responsible for past abrupt climatic changes
When sea water freezes it expels salt and adds salt to the remaining water which becomes dense and sinks. This sets up thermohaline flow. The ocean carries heat to the poles at the poles it cools and sinks.
If thermohaline shuts down can cause freezing around northern europe. Starting to see salinity changing around poles, implies its less dense, so won’t sink and could alter thermohaline cycles
Cooling in north
Heat redistributed- warming in the south –> incr global warming
Fluctuations in solar energy and smaller variations in earths climate
The sun goes through cycles of higher and lower activity seen every 11 years. The sun’s appearance also changes including solar flares, sunspots during peaks of solar activity, changes in aurora. thought to be linked to climate through unclear mechanisms.
Past- historic sunspots may coincide with changes in climate. Little ice age in 14-19th century, prolonged cooling in N europe. Can also see medieval warming period prior. Warming and cooling coincide with a few sun spots. Fewer sun spots= less solar activity. Reflected in C14 too, more radioactive C14 when more solar radiation
Effects of solar activity on hydrology
Sunspot frequency is correlated with changes in water flow and rivers eg panama river, s america. Higher solar activity –> greater ppt –> incr river flow
However, variation in solar activity too small to account for climate variation beyond decades time scales, so was it responsible for little ice age
What do Oscillators do
drive inerannual to decades climatic functions- not persistent long term changes. Best known for el nino.
El nino
- Upwelling off south america reduces nutrient supply to surface water and warmer sea. Leads to crash in fish population, notably anchovies- impacts sea birds, mammal.
- Warmer in east, cooler in west.
- Increased floods in Peru, droughts in Brazil. Warmer ocean water can increase earth’s temps
La Nina
- strengthening of normal trade winds.
- Warmer water in west, cooler in east ??
Irregular every 5-7 years
Records of O18 of annual banded corals show periodicity and strength have differed in the past
Volcanic eruptions
Large volumes of dust and sulphate into upper atmosphere | \/ Absorbs incoming solar radiation | \/ - warms stratosphere - cools troposphere and earths surface
Large eruptions are discrete, relatively uncommon and only the largest cause as much as 1 degree of cooling for a year or more
Laki Eruption in Iceland 1783
- 122 megatons of SO2 into atmosphere
- Annual mean surface cooling by 1.3 degrees in Eu and North America
- Subsiding plume led to severe volcanic pollution and acid rain
Volcanoes as trigger for little ice age?
Sulphates from several successive eruptions as alternative explanation. Four large, sulphur rich, explosive eruptions. Cool temps maintained by sea ice/ocean feedback (albedo). Several at the same time may affect climate for longer period, alternate theory to sun cycle.
Can strip out volcano effect through modelling
Past human impacts of cc
rice cultivation increased methane
incr co2 from deforestation (clearing for agriculture)
so should date anthropocene much further back?
co2 drops coincide with disease epidemics
Black death killed 25-40% of European population in middle ages.
Small box and other european disease killed 90% of native population of the americas- first nation did lots of farming so could be due to forest growing back
green house effect from co2 and ch4 from agriculture believe to be enough to ward off glaciation in NE canada that should have started about 5000 years ago
sensible heat
what you can feel
latent heat
does work eg evaporation
