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1a.a) Methods to reconstruct past
climates?
Long term
Ice cores
• As snow falls it traps parts of the atmosphere underneath.
• Every winter has a different amount of gas trapped
• Overtime, layers of snow get compressed into ice from the wight of top
layers
• Scientist drill down to collect samples
• Very reliable
Sea floor sediment
• Fossil shells of small sea creatures called foraminifera accumulate at the
bottom of the sea bed
• The chemical composition in their shells indicates the temperature they
formed in and tells us the climate
• Reliable - little human interference
Pollen
• Each layer on the sea bed indicates what plants grew at the time
• Scientists take core sample and analyse the distinctive shape of grains to
find out what plant grew and that tells us the climate which it grew in
• Not as reliable as they is human interference and long pollen sequence
chains are rare
Fossils
• Different plants show climates they thrived in
• Animals show climates they survived in
• Reliable - little human interference
Medium term
Tree rings
• Trees are sensitive to changes in heat, sunlight and rainfall
• Thicker rings show hotter climates
• Reliable - only localised
Historical records
• Paintings and books
• Unreliable - not scientific often exaggerated and locally source
Glacier retreat
• Glaciers respond to climate changes
• Growing and retreating
• Scientifically unreliable
Sea level rise
• Warmer temperatures melt ice increasing water capacity in the oceans
• Hot temperature influences thermal expansion
• Reliable
,Short term
• Hockey stick graph shows how quickly and by what large amount the CO2
levels have increased by since the industrial era, showing evidence for
anthropogenic climate change
,1a.b) Past climates
Ice house earth
• Ice sheets and glaciers present
• Glacial and interglacial periods
• Greenhouse gases less abundant
Greenhouse earth
• No continental glaciers
• More greenhouse gases
• Average sea temps. 28ºC - 0ºC
Quaternary period
• 2.6mil years ago to present
• Split into Pleistocene and Holocene
• Glacial periods of 100,000 years
• Interglacial periods 10,000 years
Glaciation of Antarctica
• Fossils show 40mil years ago a sub-tropical climate but 35mil years ago
entered permanent icehouse state changed due to:
1. CO2 levels dropped from 1000-1200ppm to 700-600ppm - caused
cooling
2. Continental drift meant Antarctica moved away from south
America, south. This created the drake passage and allowed the
Antarctic circumpolar current to form bringing cold water to the
surfaces
3. South sandwich islands (volcano ash) disrupted the deep ocean
currents and warm water from the Indian ocean couldn’t reach
Antarctica
, 1a.c) Natural forcing
PLATE TECTONICS
• Global distribution has changed drastically since Pangea was a single land
mass
• explains change of greenhouse earth to ice house earth.
• Land masses at the northern and southern latitudes meant ice cover
expanded as it is colder there.
• This meant more light was reflected as the white ice reflects solar
radiation, which made it colder through positive feedback, creating more
ice - albedo effect
• Tertiary era created extensive folds - mountain ranges
• This led to increased rainfall, erosion and chemical weathering from CO2
charged rainwater.
• This removed vast amounts of CO2 from the atmosphere and stored it
deep ocean carbonate sediment
• The increased nutrients led to a vast bloom of phytoplankton which
further extracted CO2. When they died the CO2 was trapped in deep sea
sediment
OCEAN CIRCULATION
• Transfers surplus energy from the tropics to the poles
• 5mil years ago the isthmus of panama formed, closing the gateway
between pacific and Atlantic oceans
• This intensified the gulf stream which led to more evaporation and
precipitation in northern Europe which diluted the salinity in north
Atlantic and arctic oceans.
• This weakened the downwelling of the north Atlantic which drives the
gulf stream and the entire global thermo-haline circulation
• Less saline water and reduction in heat transferred by the gulf stream,
made sea ice expand.
• This was amplified by positive feedback and caused the glaciation of
northern Europe 3mil years ago and the last glacial period 110,000 -12,000
years ago.
VOLCANOES
• Large eruptions eject ash and sulphur into stratosphere
• Ash settles but sulphur turns into sulphur dioxide and then sulphuric acid
• This forms a haze of sulphate aerosols
• They reflect solar radiation lowering the temperatures in troposphere
• 1816 Tambora eruption led to the year without summer temps dipped by
0.4 - 0.7
• 1991 Pinatubo eruption caused global dimming of 1.3ºc
NATURAL GREENHOUSE GASES
• More GHG in the atmosphere = higher temps
• Ice ages coincide with low CO2 levels
• Pliocene - 3.5mil years ago, had 400ppm of CO2 And average temperatures
were 2ºc - 3.5ºC higher than todays
• Ocean currents, mountain ranges and tectonic plates explain how CO2
was extracted.
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