Topic 4 : Ecology
4.4 Climate change
Greenhouse Gas
- Greenhouse Gas: gases in atmosphere that retain heat e.g. carbon dioxide, water vapor, methane, nitogen dioxide
- The gases that have the greatest impact on the warming effect on earth are \(CO_2\) and water vapour
- Carbon dioxide is released into the atmosphere by cellular respiration by organisms and combustion of organic materials and burning of fossil fuels. It is removed by photosynthesis and absorption by the oceans
- Water vapour is created by evaporation of the water in oceans, seas and lakes and transpiration by plants. It is removed through precipitation.
- Methane has the third greatest impact on the greenhouse effect
• It is emitted from marches, other water-logged habitats and from landfill sites containing organic wastes - Nitrogen dioxide, which is another significant greenhouse gas is released naturally by bacteria in some habitats and also by agriculture and vehicle exhaust
- All the greenhouse gases together make up less than 1% of the earth’s atmosphere
- The greenhouse effect is a natural phenomenon that keeps the surface of the earth warm due to the presence of an atmosphere containing these gases that absorb and radiate heat.
Impact of greenhouse gas
- The two factors that determine how much of an influence a gas will have on the greenhouse effect are
1) The ability of the gas to absorb long-wave radiation (heat)
2) The concentration of the gas in the atmosphere - Methane actually has the ability to cause much more warming per molecule than carbon dioxide; however, there is a much lower concentration of methane in the atmosphere
- When light (shorter wavelengths) enters the earth’s atmosphere, some of the light reflects off the earth’s surface back towards outer space.
- Some of the light is converted into heat, which in turn warms the surface of the earth (the air, mountains and water).
- This heat (longer wavelengths) radiates off the earth back towards the atmosphere.
- Greenhouse gases such \(CO_2\) and water vapour absorb this heat (infrared radiation) trapping it within the atmosphere, further warming the earth.
- As the infrared radiation is reflected back off the earth, a large percentage of this heat is captured by the greenhouse gases in the atmosphere. This energy is re-emitted, thus heating up the earth’s atmosphere. This effect is called global warming.
- There is a correlation between rising atmospheric concentrations of carbon dioxide since the start of the industrial revolution 200 years ago and average global temperatures.
- There is also strong correlation between human emissions and atmospheric carbon dioxide level
- This does not mean that the amount of greenhouse gas is the only reason for the earth warming and cooling
- Other factors such as the cycles in the Earth’s orbit around the sun, variations in the amount of solar radiation due to sunspot activity, past volcanic activity, and changes or oscillations in ocean currents
Increase in greenhouse gas level
- The number one source of carbon emissions due to human activities is through combustion of fossil fuels in automobiles, buses and planes.
- Another source of carbon dioxide is the deforestation through burning large tracks of land and heating homes with fossil fuels, such as natural gas
- Humans demand for meat has led to large numbers of cattle, which is responsible for releasing methane into the atmosphere, which is changed into
carbon dioxide - As the human population increases and countries become more industrialized, human production of greenhouse gas, shows no sign of slowing down
- The increase in greenhouse gas will likely lead to:
- Higher global average temperature
- More frequent and intense heat wave
- Some areas become prone to drought
- Some areas become prone to rainfall and flooding
- Ocean Acidification – more carbon dioxide dissolved in water
Coral reef
- Ocean acidification is the ongoing decrease in the pH of the Earth’s oceans, caused by the uptake of carbon dioxide from the earth’s atmosphere.
- Reef-building corals that use calcium carbonate in their exoskeletons need to absorb carbonate ions from seawater.
- The concentration of carbonate ions is low in seawater because they are not very soluble.
- Dissolved \(CO_2\) makes the carbonate concentration even lower as a result of some interrelated chemical reactions:
\(CO_2 + H_2O <–> H_2CO_3 <–> H^+ + HCO_3^− <–> H^+ + CO_3^{2-}\) - If the carbonate ions concentrations drop it is more difficult for reef-building corals to absorb these ions to make their exoskeletons
- Also, if seawater ceases to be a saturated solution of carbonate ions, existing calcium carbonate tends to dissolve, so existing exoskeletons of reef-building corals are threatened.
- Global warming will cause the water temperature to increase, this will also affect the growth of coral reef.