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Detailed notes [including case studies] on Climate Change for OCR A-Level Geography paper 3
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CLIMATE CHANGE1. How & why has climate changed in the geological past
Key ideas Content
1.a. The ● Methods used to reconstruct past climate, including marine & lake sediments, ice
Earth’s cores, tree rings & fossils
climate
is dynamic SEA-FLOOR Fossil shells of tiny sea creatures called foraminifera, which accumulate in sea-floor
SEDIMENTS sediments, can be used to reconstruct past climates. The chemical composition of
foraminifera shells indicates the ocean temperatures in which they formed
ICE CORES Ice cores from the polar regions contain tiny bubbles of air - records of the gaseous
composition of atmosphere in the past. Scientists can measure the relative
frequency of hydrogen & oxygen atoms with stable isotopes. Colder the climate, the
lower the frequency of these isotopes
LAKE Past climates can be reconstructed from pollen grains, spores, diatoms & varves in
SEDIMENTS lake sediments. Pollen analysis identifies past vegetation types & from this infers
palaeoclimatic conditions. Pollen diagrams show the number of identified pollen
types in the different sediment layers. Diatoms are single-celled algae found in lakes
with cell walls made of silica. They record evidence of past climates in their shells
(see foraminifera above). Varves are tiny layers of lake sediment comprising
alternating light & dark bands. The light bands, formed from coarser sediments,
indicate high energy, meltwater run-off in spring & summer. The darker bands, made
up of fine sediment, show deposition during the winter months
TREE RINGS Dendrochronology [study of tree rings] is the dating of past events such as climate
change through study of tree ring (annule) growth. Annules vary in width each year
depending on temperature conditions & moisture availability
FOSSILS Plants & animals require specific environmental conditions to thrive e.g coral reefs,
are highly sensitive to temperature & sunlight. Where they exist in the fossil record
they can be used as proxies for climate. Animals are more adaptable
FORAMINIFERA
➔ Foraminifera = foraminifera are amoeba-like single celled protists. They secrete a tiny shell [or
test]. Fossilised tests are found in sediments.
➔ Foraminifera are still found in marine & brackish waters [Brackish water=saltier than freshwater,
but not as salty as seawater. Mostly found in estuaries where freshwater meets seawater]
➔ Foraminifera that lived in the geological past were also controlled by the environment so fossils
can be used to identify the conditions in which the enclosing sediments accumulated
➔ They can be used, for e.g to recognise glacial & warm episodes during the Quaternary,
changes in salinity in the Cretaceous period, variations in the O2 content of the water in the
Jurassic, sea level oscillations during the Carboniferous & so on
➔ Can identify glacial/interglacial period = temp - affect chemical make-up
,DIATOMS
➔ Diatoms are single-celled algae that live in houses made of glass.
➔ Palaeoclimatology is the study of past climates. Past climates can help us to predict future
climate conditions. Microfossils, such as diatoms & foraminifera, can help us with
palaeoclimatology studies. They can tell us about lots of different conditions including ocean
acidification levels, sea surface temperatures, how much ice was present on Earth & how much
CO2 & O2 was present in the atmosphere
,FOSSILS: Different species of plants & animals need different conditions to survive. Some can be
sensitive to climate & don’t adapt easily to change. E.g coral reefs live in tropical waters - need
particular temp, specific depth of water & right amount of light. If the depth of the water changes, they
can’t survive. Thus where fossil corals are found it’s possible to estimate fairly precisely the
environment they lived by assuming that they needed the same conditions as those that thrive today
CORAL REEFS
➔ Made from coral polyps - [stationary] tiny creatures, related to jellyfish & found in tropical seas
➔ If nothing is done, within 15 years all the coral will be in danger of disappearing -> fragile
ecosystem [like the rainforests of the sea] = anthropogenic factors -> over-fishing, ocean
pollution, warming temperature due to global warming [enhanced greenhouse effect]
➔ Interdependence e.g turtles prevent over-growing of corals - food source for turtles
➔ Another e.g of interdependence - clownfish hides in sea anemone from predators, in turn, a
benefit for the anemone is that clown fish cleans the anemone from parasites
POLLEN DIAGRAMS
➔ Pollen diagrams are a series of graphs for different plant species displayed side by side. The x
axis shows the % of total pollen for each plant type displayed. The y axis shows age [time] &
sometimes depth of sediment
➔ Pollen analysis can give indication of past flora - growing conditions [so tell us conditions in the
past as different trees need different conditions to grow
● Past climate to reveal periods of greenhouse and icehouse Earth, including:
○ long term, 100 million year transition to colder global climate conditions
Mid-Cretaceous period [100 million years ago]
- During the mid-Cretaceous period around 100 million years ago, average global temperature
were 6-8℃ higher than today.
, - No polar ice caps and atmospheric CO2 levels were 5x higher than today
- At this times the continents had a very different configuration, which affected ocean circulation
& the Earth’s energy budget
- A further, but short lived, spike in global temperatures occurred 55 million years ago which is
known as the Palaeocene-Eocene thermal maximum, where the average global temperatures
peaked around 23℃
- At the start of the Oligocene period, 35 million years ago, there was a rapid transition to colder
conditions which have continued to the present day. This change was related to a major
reduction in atmospheric greenhouse gases [especially CO2]
○ glaciation of Antarctica around 35 million years ago
40 million years ago, the fossil record shows that the continent experienced subtropical conditions. The
descent of Antarctica into a permanent icehouse state occurred rapidly around 35 million years ago.
This transition to icehouse conditions has been explained by changes in atmospheric CO2 & tectonic
processes
● CO2 levels dropped abruptly 35 million years ago, from 1000-1200 parts per million (ppm) to
600-700 ppm.
● Continental drift: the movement of Antarctica towards the south pole & away from South
America & Australia, isolated the continent.This allowed the Antarctic Circumpolar Current to
insulate Antarctica from the warmer water further north
● The Antarctic Circumpolar Current is an ocean current that flows clockwise from west to east
around Antarctica. The current is circumpolar due to the lack of any landmass connecting with
Antartica & this keeps warm ocean waters away from Antarctica, enabling that continents to
maintain its huge ice sheet
● The growth of the South Sandwich Islands'
submerged volcanic arc disrupted deep-water
ocean currents around Antarctica, isolating the
continent from warmer water from the South
Pacific, Atlantic & Indian Oceans
○ quaternary glaciation
● The Quaternary period spans the last 2.6 million
years.
● Main feature of Quaternary: cyclic changes of climate, with long cold periods/glacials
interrupted by shorter, warmer interglacials.
● Typically, glacials have lasted for around 100,000 years, interglacials for 10,000-15,000 years.
● During glacial periods, average annual temp in northwest Europe remained well below zero
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