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Geography Lecture 2 (Additional Information (Proxy evidences are used as…

- - - - Foraminifera
        
        In ice ages, water is frozen and thus removed from the oceans. This leads to a reduction in concentration of ¹⁶O isotopes in the water.
        
        The freezing of ice caps not only lead to a decrease in sea level, it also changed the chemical composition of the oceans
        
        This change in composition causes the foraminifera to change the chemical composition of their shells. When they die, their shells fall to the ocean floor and accumulate as ocean sediment
        
        By extracting cores of ocean sediment, we can study the chemical compositions (calcium carbonate) of the shells of foraminifera, and thus infer the temperature of the ocean during that period of time
    - - Pollen Grains
        
        Pollen grains are extremely resistant to decay and are unique for every plant species
        
        As pollen grains fall from plants into closed-system lakes, the grains becomes lake sediment
        
        Thus, cores of lake sediment can tell us what kind of vegetation lived near the lake at specific points in time and thus tell us the climate of the region during that time
      - Diatoms
        
        The type of diatom present in the water depends on the salinity of the water. If the salinity of the lake changes, the diatoms present in the lake will change as well. This will be recorded in the lake sediments as they die and accumulate at the lake bed
        
        Diatoms can only be used as a proxy evidence in a closed-basin lake (no outlet)
    - - Isotopic composition
        
        The higher the ratio of ¹⁶O to concentration of ¹⁸O, the colder the air was then the snow precipitated from the clouds
      - Greenhouse Gasses
        
        Ice-core records also contain small pockets of greenhouse gasses. By extracting ice cores, we can analyze the gasses and reconstruct how the composition of the atmosphere was like at that time
    - - Ice Cores
        
        Limited accuracy of temperatures derived from oxygen isotope
        
        The large volume of water stored in ice sheets altered the isotope composition of the oceans
        
        Increasing elevation of ice sheets would be expected to cause a decrease in temperatures
      - Oceans
        
        The sediments may have been disturbed since the time which it was formed
      - Lakes
        
        There may be a time lag between the change in climate and the organism's response
- - - - The most recent ice age reached its maximum severity 21000 years ago.
      - Most of the British Isles were covered with glaciers up to 300m thick. Icebergs were found as far as Spain
    - - A sudden and drastic warming took place. In a few hundred years, the temperatures rose rapidly to levels close to today's.
    - - Ice caps grew and extended over Scotland, and mean annual temperatures were at -8 degrees
      - Started very suddenly at 12900BP
      - Ended very suddenly at 11500BP
    - - Temperatures were around 8 degrees cooler than today's
    - - Sudden dip of 6 degrees, lasting for 200 years.
    - - Temperatures were 2 degrees higher than today's
    - - Vineyards were as far North as York
      - Wetter summers and later frosts coincided with the Black Death
    - - Glacial expansion in the Alps
    - - 12000-6000BP
        
        Higher atmospheric pressure
        
        Higher lake levels due to higher evaporation and rainfall
        
        Hippos and humans in Sahara
        
        Rainforest in Australia
      - 6000BP to now
        
        Desiccation in Sahara
        
        Falling lake levels due to increased temperatures and aridity
        
        Tropical rainfall is suppressed
        
        Rainforest in Australia retreats
- - - - Clouds reflect about 1/3 of Earth's insolation. A warmer climate would cause more clouds to form, reflecting more insolation, thus reducing the warming effect
    - - Precipitation increases with increased water vapor in a warmer atmosphere, but not in all regions, some will dry out. Changes in precipitation may cause an increase in plant growth, thus removing carbon dioxide from the atmosphere
    - - Natural processes, such as tree growth, remove about half of human carbon dioxide emissions. Changes in plant growth can lead to more plants removing more carbon dioxide from the atmosphere
    - - Ice reflects much insolation. As the atmosphere warms, ice melts into water. This reduces the albedo and less insolation is reflected, thus warming the Earth further
  - - - If enough ice melts, Earth would absorb more and more heat. This is as there is no more ice to reflect the heat. We may hit a point of no return, and this would cause many people living near coasts to be affected
    - - Deposits of frozen methane within the permafrost. As the world warms and permafrost thaws, the gas would be released and thus cause further warming
    - - If the Gulf Stream fails, it would cause significant cooling in Western Europe (5-10 degrees). This may potentially lead to a global catastrophe
  - - - Solar Irradiance
        
        The amount of insolation reaching the Earth
        The Sun has an 11-year sunspot cycle, causing about 0.1% of the variation in Solar output
      - Milankovitch Cycles
        
        i. Eccentricity of orbit
        
        The cycle takes about 96,000 years. There is a 3% difference between aphelion and perihelion. This means the Earth receives 6% more energy in January than in July. At most elliptical, the insolation at perihelion is 20-30% more than aphelion
        
        iii. Precession of the Equinoxes
        
        The cycle takes 23,000 years.
        Today, the Earth is tilted at 23.5 degrees, pointing at Polaris.
        At the other end, the Earth will point at Vega. This would cause the seasons to flip
        
        ii. Axial Tilt
        
        The axial tilt of Earth today is about 23.5 degrees
        Smaller angle = cooler
        
        Limitations
        
        Foraminifera do not represent a pure sea level record. They are also affected by deep sea temperature changes. For example, Skinner and Shakleton(2005) showed that the isotope record for the end of the last glacial appears to be 2200 years earlier than the likely timing
        
        The expected changes in temperature caused by orbital forcing are too small to explain the ice expansions, thus other forcings must be at play
        
        Milankovitch Cycles show a smooth change, but the curve is in a sawtooth pattern
      - Albedo
      - Aerosols :
      - Greenhouse Gases :
    - - Volcanic activity
        
        Volcanoes hurl large amounts of volcanic matter into the atmosphere, reflecting sunlight and causing net cooling. For example in 1815, Mount Tambora in Indonesia erupted, killing 90,000 people and ejecting 50km^3 of rock 40km into the atmosphere.
      - Fluctuations in oceanic activity
      - Changes to biosphere and cryosphere
      - Tectonic activity
        
        Continental positions, sizes and configuration of ocean basins are the result of crustal processes. These processes have also changed the size and location of mountains and plateaus, thus changing the pattern of ocean circulation and surface currents.
        
        Over the last million years, the uplift of the Tibetan plateau and the Himalayan ranges has caused the intensification of desert conditions in Western China and Central Asia