What is a Carbon Foot Print? -------------------------- M.V.N. Murthy The Institute of Mathematical Sciences Chennai 600 113 There is now a scientific consensus that the temperature near the surface of the Earth is increasing on the average. The average is taken over all regions of the world and over a period of one year. This average temperature shows a steady increasing trend. This is called global warming. If this warming continues, it is expected cause the increase in sea levels, expansion of deserts, retreat of glaciers, extreme weather conditions and many such effects with catastropic consequences for all the living beings on earth. Of course these changes will not be uniform all over the globe, but could vary from region to region. Fig.1: Golbal mean temperature variation with respect to the mean temperature during the period 1951-1980. It is now reasonably well established that most of the observed increase in the average temperature, at least partially if not wholly, is caused by the increased emission of the so-called green house gases (GHG). This itself is a result of increased human activity since the middle of 20th century as shown in Fig.1. BOX 1: Green house gases: The name green house gas refers to a set of gases which trap heat in the earth's atmosphere much like a green house traps heat in the enclosure. The trapping of heat is infact necessary as other wise earth would be much cooler than what it is now. Green house gases infact help maintain the temperature balance on earth. However, if the concentration of these gases increases in the earth's atmosphere it will lead to the warming as we are witnessing now. The gases which contribute to the green house effect in our atmosphere are water vapour, carbon dioxide, methane, nitrous oxide, ozone and chlorofluorocarbons (Freon is the trade name for these). Water vapour and carbon dioxide are both necessary to sustain life on earth. However at increased levels the carbon dioxide concentration warms the air further and allows it hold more water vapour thus amplifying the green house effect. END OF BOX --------------------------------------------------- The effect of these green house gases is quantified in terms of "Carbon Footprint". It is the sum total of green house gases emissions caused by a person or product or activity measured in terms of the amount of carbon dioxide (or its equivalent of other GHGs) emitted. This quantification is necessary to develop strategies to reduce the effect of global warming. An important factor in developing these strategies is to look at the mode of energy production. Since much of human activity involves use of energy either directly by burning fuels (as in cars and buses, cooking, etc) or through production of electricity (for domestic and industrial use), it is useful to look at the sources and see which of them leave a smaller carbon foot print - how much carbon dioxide or its equivalent GHG is emitted in the process. Following table gives an idea of how much carbon dioxide is emitted per unit energy produced: Table 1: CO_2 emission in common fuels ---------------------------------------------------------------- Fuel/Resource CO_2 emitted (grams per kilo-Watt-hour of electricity) ---------------------------------------------------------------- Coal 955 Oil 893 Natural Gas 599 Nuclear Fuel 60 (Light water reactor) 65 (Heavy water reactor) Hydroelectricity 15 Solar Power 40 (estimate) Wind Power 21 ---------------------------------------------------------------- Source: Wikipedia. Since production of electricty is one of the main sources of GHG emission, the above table clearly indicates the strategy to be followed if global warming catastrophe is to be avoided. At present most of the electricity in the world and in India is produced through Coal and Oil apart from Hydro power. The reason for relying on these sources is that they are steady and reliable sources. There is heavy price to pay in each of these sources. Fossil fuels like coal, oil and natural gas emit huge amounts of GHGs and therefore there is an urgent need to replace these sources. Hydro-electricity is far more benign in terms of GHG emission. However, dams built to store large amounts of water for powering hydro power production are in most cases environmental disasters. Apart from destruction of forests, they lead to loss of habitat, displacement of large numbers of people. The economics of all the factors taken together makes it unsuitable as a major source of electricity. Similarly nuclear energy does not cause increase in GHGs to the same extent as fossil fuel fired power stations. However safety of nuclear reactors and long term disposal of radio active waste are the main issues here. Recent earth quake and tsunami induced nuclear accidents in Japan have again brought the focus back on the safety of nuclear reactors. Solar and wind power therefore hold the promise for future direction. They are available in plenty, are renewable and do not cause GHG emission except during the production of material and transportation. The main problem here is one of intermittency and variability from region to region and time to time. Photovoltaics technology to store solar energy, though this increases marginally GHG emissions, may be the answer to the future. The initial cost is also huge compared to other sources of electricity. There is huge world-wide effort to overcome these problems especially in reducing the cost. In India there is an ambitious plan to generate about 20000 MW by 2020 through these renewable sources of energy like solar and wind .