Greenhouse Gases and Global Warming

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  • 1. Greenhouse Gases and Global Warming
  • 2.  What is a greenhouse gas?  Infrared Radiation is passed through a molecule and if it can pass through without interacting with the molecule then it is not considered a greenhouse gas.  Oxygen and Nitrogen, the two major gases in our atmosphere have no interaction with the IR radiation.  Water vapour however, does absorb some IR radiation, therefore there is an interaction, making this a greenhouse gas.
  • 3.  The greenhouse gases absorb long wave radiation (IR radiation) but allow for the passage of long wave radiation (eg. UV Light), which does not interact with the gases.  The IR radiation absorbed by the greenhouse gases cause vibrations in the bonds, then the energy is ‘re-radiated’ back to Earth.  (Just FYI, the IR radiation comes from the Earth, whereas UV light are emitted from the Sun)
  • 4. Absorption of Infrared Radiation by Greenhouse Gases  Water vapour (H₂O) is the most active molecule in the absorption of Infrared radiation and thus in heating the atmosphere. It accounts for about 55% of IR absorption.  Carbon Dioxide (CO₂) accounts for about 18%  Methane (CH₄) for 6%  Ozone (O₃) for 5%
  • 5. Natural Sources of GHGs  Volcanic Eruptions  Forest Fires  Dust  Pollen  Incomplete oxidation of methane in the atmosphere. (The methane originates from aerobic decomposition)  Bacterial action in the soil produces NO₂
  • 6. Anthropogenic Sources of GHGs  Industrial plants that produce smoke/soot from the combustion of fossil fuels.  The incomplete combustion of fossil fuels. (Forms CO)  Paint  Cleaning Supplies  High temperature combustion engines produce NO which is then oxidised to 2NO₂
  • 7.  Despite looking at the relative effects on heating due to the absorption of infrared radiation, water vapour is not the biggest contributor to global warming.  This is because the water cycle remains fairly stable and consistent meaning that the amount of water vapour in the atmosphere at any one time is pretty consistent.  However the concentrations of Carbon Dioxide and Methane are not so stable and are increasing in amounts thus absorbing more IR and causing further heating of the planet.
  • 8.  Temperatures have clearly picked up following the industrial revolution and have escalated as technologies advance and the population increases.  In 2007 GHG levels were at 430ppm, but before the Industrial Revolution that number was just 280ppm.  To cope with the increasing demand for energy, fossil fuels have and are being burnt more and more, releasing growing amounts of Carbon Dioxide into the atmosphere and heating up the Earth as a result.
  • 9.  The increase in heat due to excess Carbon Dioxide in the atmosphere causes the melting of permafrost, especially in places such as Siberia. The frozen ground contains trapped Methane which is released as this ice melts (at an accelerated rate) altering the balance of Methane in the atmosphere causing further heating.  In just a single year (2004-5) NASA reported a 14% decline in permanent sea ice.  In turn, the more sea that is exposed, the less energy is reflected, and instead absorbed by the darker coloured oceans resulting in even further heating of the oceans and earth.
  • 10.  The speed of human induced climate change is much faster than it has naturally. Since the last ice age (10,000 years ago) and today there has been an overall rise of 5 degrees Celsius, however at current rates the increase is 1.4 degrees per 100 years.  Anthropogenic changes are happening much faster than natural rates seem to have ever done, making it extremely difficult for organisms to adjust, and the consequences could be extreme.  Just of 3 degrees has massive impacts on our well tuned ecosystems and could result in the loss of 20-50% of species.
  • 11. https://www.youtube.co m/watch?v=2yx8kGyeOy Y