1.1 Greenhouse Effect & Global Warming

• Some gases such as CO2, CH4, O3, water vapour, N2O and CFCs are known as greenhouse gases serve as insulation to maintain the temperature of the Earth's atmosphere, which is the Natural Greenhouse Effect.
• Human activities increases the concentration of greenhouse gases in the atmosphere, increasing the absorption of infra-red radiation in the atmosphere, which leads to increases in global temperatures. This is the Enhanced Greenhouse Effect which ultimately causes global warming.
• Humans have increased the concentration of the greenhouse gas of CO2 and H2O by the complete combustion of fossil fuels and chopping rain forest.

  Deforestation increases CO2 concentrations by releasing stored carbon whilst reducing the earth's capacity to absorb future CO2 due to less photosynthesis
• Humans have increased the concentration of the greenhouse gas of CH4 by ruminant animals (cow burp and poo) and fossil fuel mining
• Humans have increased the concentration of the greenhouse gas of N2O by using excessive fertilizers which increase the activity action of micro-organisms in the soil
• Some consequences of global warming include

  • Melting ice caps, polar caps, glaciers
  • Rising sea levels (because water expands when it's hot)
  • Loss of biodiversity
  • Change weather patterns (more extreme droughts and floods)
• The ocean has a pH of 8.06. An increase of carbon dioxide in the atmosphere will cause an increase in carbon dioxide absorbed by the oceans, creating carbonic acid:

  CO2 + H2O <=> H2CO3

  Carbonic acid partially ionises as a weak diprotic acid, increasing the concentration of hydrogen ions.

  H2CO3 + H2O <=> HCO3- + H3O+

  HCO3- + H2O <=> CO32- + H3O+

  This increases the rate of dissolution of skeletons and shells
• Exoskeletens and shells of marine organisms are made of calcium carbonate and the extra hydrogen ions from the low pH can dissolute them

  CaCO3 [shell] + 2H+ --> H2O + CO2 + Ca2+
• A decrease in pH increases the concentration of hydrogen ions in the sea. According to LCP, an increase in concentration of a product will cause the equilibrium to shift in the direction to counteract the change. In this case, an increase in hydrogen ions will cause the system will shift the equilibrium to the left. Consequently, this decreases the concentration of CO32-, which is needed to combine with Ca2+ to make marine organisms's shells and exoskeleton.
• Ocean acidification can cause the loss of many shelled organisms like oysters, clams and sea-urchins, affecting the food web and causing great economic distress around the world. A drop of 0.4 pH units would already be fatal.

  However, some photosynthetic organisms like seagrass and algae may increase in number, benefiting from ocean acidification.
• Short wave UV radiation from the Sun reaches the Earth's atmosphere. Some is reflected back by clouds but most is absorbed by the land and oceans. The earth re-radiates the energy into long wave infra-red radiation. The greenhouse gases in the atmosphere contain polar bonds which absorb and re-emit infrared radiation from the Earth's surface due to their polar bonds. This prevents the heat from escaping back to space and traps it in the lower atmosphere, preventing rapid temperature fluctuations.