| The atmospheric concentration of carbon dioxide |
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| Tuesday, 15 April 2008 | |
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The atmospheric concentration of carbon dioxide (CO2) has increased by 31 percent since 1750. The current concentration of CO2 has never before been achieved during the last 420000 years and not probablement7 during the 20 million years. The current rate of increase is unprecedented for at least the last 20000 years.
About three-quarters of anthropogenic emissions of CO2 in the atmosphere over the last 20 years are due to the combustion of fossil fuels. The remainder is due primarily to changes in land use, especially deforestation.  The rate of increase in the concentration of CO2 in the atmosphere was about 1.5 ppm (0.4 per cent) per annum over the past 20 years. During the 90 years, increasing from one year to another ranged from 0.9 ppm9 (0.2 percent) to 2.8 ppm (0.8 percent). Much of this variability is due to the effect of climatic variability (eg, El Niño) on the absorption and emission of CO2 by the oceans and land. The greenhouse gases other than CO2 "The atmospheric concentration of methane (CH4) has increased by 1060 ppb9 (151 percent) since 1750 and continues to increase. Past 420000 years, the concentration of CH4 had never reached the current level. Growth this annual concentration slowed and became more variable in 90 years than in 80 years. Slightly more than half of current emissions of CH4 are anthropogenic (eg burning of fossil fuels, livestock, cultivation Rice, landfills). Moreover, the emissions of carbon monoxide (CO) has recently been identified as one of the causes of the increase in the concentration of CH4. The atmospheric concentration of nitrous oxide (N2O) increased by 46 ppb9 (17 percent) since 1750 and continues to grow. The current concentration of N2O had Never reached this level since at least 1000 years. About a third of current emissions of N2O are of human origin (eg cropland, food Livestock, chemical industry). Since 1995, atmospheric concentrations of several of these gases halocarbon, which are both gases that deplete the ozone layer and greenhouse gas (per Example: CFCl3 and CF2Cl2) rose less rapidly or decrease as a result of emission reductions under the rules laid down by the Montreal Protocol and its amendments. Their replacement compounds (eg CHF2Cl and CF3CH2F) as well as other synthetic compounds (eg hydrocarbons Perfluorocarbons (PFCs) and sulphur hexafluoride (SF6)) are also greenhouse gases and their concentrations are increasing. Radiative forcing due to increases in greenhouse gas well mixed between 1750 and 2000 is estimated at 2.43 W m-2: * 1.46 W m-2 due to CO2; * 0.48 W m-2 due to CH4; * 0.34 W m-2 due to halocarbon gas; * And 0.15 W m-2 due to N2O. The depletion of ozone (O3) stratospheric as it has been observed between 1979 and 2000 would have resulted in an estimated negative radiative forcing (-0.15 Wm-2). Assuming that the existing regulations on the gas halocarbon be fully respected, the positive forcing halocarbon gas will be reduced, as well as the magnitude of the negative forcing due to stratospheric ozone depletion, as the ozone layer will replenish the twenty-first century. According to estimates, the total volume of O3 in the troposphere rose 36 1750, largely as a result of anthropogenic emissions of various gases Contributing to the formation of O3. This corresponds to a positive radiative forcing of 0.35 W m-2. Forcing due to O3 varies considerably from one region to another and react more quickly to changes in emissions that greenhouse gases long-lived as CO2. |
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| Last Updated ( Thursday, 03 July 2008 ) |
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