Lecture 26: Last 1000 years Flashcards
What has the last 1000 years consisted of and what period did it begin after?
Beginning after the medieval warm period, the last 1000 years has been characterised by major climatic events alongside the acceleration of anthropogenic changes
What has knowledge of the last 1000 years been substantially aided by?
People writing things down i.e. there are more instrumental and documental records, there is a plethora of palaeoclimate data
What two types of information can tree rings provide us with about the past?
Dendroclimatology and Dendrochronology
What are some of the oldest trees in the world?
Bristlecone Pine (>5kya) but suggestions that ones in Sweden are older
Why are Giant Sequoia trees good for palaeoclimate data? Where are they found?
They are large and provide magnified image of the past. California
What does the presence of scars on tree cores suggest?
Fires or pests may have hindered growth patterns
What climate characteristics can tree rings provide us with?
Temperature, precipitation, extreme events
What is a huge benefit of the tree ring data?
It is of extremely high resolution and can provide us with seasonal variation data
What are the two parts of tree ring bands which tell use about seasonal variation?
Early and Late wood
What is dendroclimatology?
This determines the climate conditions of the past predominantly by looking at the isotope composition
What can analysing the ratio of carbon 13 tell us in dendroclimatology about climate?
It determines the co2 concentration within cells of the tree which is then an indication of different climate characteristics such as temperature and precipitation
What can analysing the ratio of oxygen 18 tell us in dendroclimatology?
It determines the source of precipitation that the tree is experienced to which then provides information on the global temperature because (think to the ice/sea oxygen balance thing)
What is dendrochronology?
Constructing a chronological order of how the tree rings growth has changed over time
What can we do in dendrochronology to construct a longer term record of climate?
Pair up different parts of tree growth or from different trees with each other as some will cover an older period (they have died and so do not contain information on more recent periods) and others will be younger trees and cover the more recent period
What state can tree remains be in in order to be used for dendrochronology?
Dead, alive or fossilised
What are dendrochronology’s especially useful for?
radiocarbon dating
What type of carbon decays?
Radiocarbon e.g. 14C
What happens to radiocarbon over time?
It decays, at a known rate
How do we determine how radiocarbon has decayed?
Half life - this is when the atoms within the molecule start to transfer from the parent nuclei to the daughter nuclei
Simplify what half life means
The time it takes for half of the atoms that make up the molecule of 14C at a given point to have ‘decayed’ (been lost) from their initial state to their new state
What is the known rate of radiocarbon (14C) decay?
5730 + or - 30 years
What marks the starting point for when radiocarbon decay? Why?
All living things absorb radiocarbon and so when they die this absorption stops and so we have a starting point of how much radiocarbon it holds and therefore from which to work back from how much it has decayed since
How is the age of things determined using radiocarbon dating?
Looking at how much unstable radiocarbon (the radiocarbon which still has to decay) and stable radiocarbon (that which has decayed) is left in the molecule, then using the known rate of decay to work back when the decay process would have begun and therefore when the living thing died and its age.
How far back can radiocarbon dating stretch back to?
50kya
What must radiocarbon samples be?
Organically sourced
What is a problem with radiocarbon dating?
There has been significant variation in the amount of insolation over time and so this means neither has the atmospheric CO2. Meaning that dating back to a time is difficult
What needs to happen to the radiocarbondated measurements after they have been collected?
They need to be calibrated for their true age
How are radiocarbon samples calibrated?
The age estimated using radiocarbon dating diverges from the calendar age in tree rings. Tree rings also contain radiocarbon and so we can compare the radiocarbon concentration of that sample with the tree rings to see when that concentration of radiocarbon was present and therefore the age of the body in which the radiocarbon sample was collected.
what is the rule in radiocarbon dating calibration?
If a sample has the same proportion of radiocarbon as that of a given tree ring, it is safe to conclude that they are of the same age
What does calibration always produce?
Uncertainty
How can uncertainty in the radiocarbon dating be represented?
Age +_ standard deviation
Lower value of standard deviation from the age - upper value of standard deviation from the age
What does non calibrated radiocarbon look like?
14C Years BP
What does calibrated radiocarbon look like?
Cal. Years BP
When did the medieval warm period take place?
~1000AD to 1300AD
What was it possible to do in Scotland during the MWM?
Grow grapes and produce wine
When did the Little Ice Age take place?
~1450AD and ~1850AD
What was it possible to do in the LIA?
frost fairs on the river thames
What is the 20th century warming period in relation to the last 1000 years?
Unprecedented and out of the norm
What are the main drivers for the climate changes in the last 1000 years?
Insolation cycles
Anthropogenic
What are 2 reasons for why people have called for an ‘Anthropocene’?
1) Humans are no longer a temporary disturbance
2) Humans shape processes across the terrestrial biosphere and increasingly the ocean and atmosphere
What have some called for to be created to recognise the role of human behaviour in the earth system?
anthroposphere
What are 8 indications of human activity that have an on the earth system?
GHG, deforestation, land cover changes, aerosol production, industrial farming, great pacific garbage patch, microplastic waste, tar sands, fracking, flaring,
What impacts are humans having on biodiversity?
1) Extinction rates increased and mass extinctions more common; 2) Land use change and habitat loss; 3) translocation of flora and fauna through intentional and unintentional human agency that homogenises species and introduces invasive species
What impacts are humans having on climate?
1) Atmospheric GHG concentration; 2) global temperature rise; 3) loss of ice masses (albedo and thermohaline circulation); 4) sea level rise; 5) permafrost melt; 6) climate-driven habitat loss
What is the emerging consensus about the dawn of the Anthropocene?
That it emerged during the industrial revolution but has been enhanced by a stage 2 rise marked by the period since 1950.
What is Stage 2 of the Anthropocene known as?
Rapid acceleration period
What did Crutzen (2002) propose was the ‘dawn’ of the Anthropocene?
Industrial revolution
What were some products that were produced during the industrial revolution period?
New steam engines designed by Newcomen (1712) and Watts (1874)
What were some flow-on effects of the industrial revolution period?
efficient land clearance systems, synthetic fertilizer, improved sanitation/water supply
What year did IPCC identify as the pre-industrial boundary?
1750
What demographic change occurred since the industrial revolution?
rapid population growth
What did Steffen et al. (2011) propose about the dawn of the Anthropocene?
It dawned with the ‘rapid acceleration period’ in the 1950s
What happened following the 1950s in terms of the dawn of the Anthropocene?
Major changes in consumption patterns which resulted in major shifts in industry which produced major climatic and environmental impacts
Aside from GHG pollution, what were some other climate and environmental impacts that became major after the 1950s?
Ozone depletion and deforestation in certain countries
Why is it important to define the dawn of the Anthropocene?
To ensure consistency across the literature. This will enable correlation between sources of evidence and establishment of baselines which will aid understanding and coherence
Why was there an increase in the amount of 14C which coincided with the rapid acceleration period?
Nuclear bomb testing in Cold War
What record contains evidence of the nuclear bomb testing impact?
Dendrochronolgies from the ‘loneliest tree in the world’ located in New Zealand recorded a sharp rise in the amount of 14C in its tree rings
What is the ‘business as usual’ RCP in the IPCC reports?
Continue acting the way we do and we will find a way to cope
What is the ‘path to sustainability’ RCP in the IPCC reports?
Drastic action to alter our current behaviour?
What is the ‘geoengineering’ RCP in the IPCC reports?
we manage to find a way to manipulate the earth system
