How do dams contribute towards redusing Co2 emission?
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According to the most detailed estimate available, done by Ivan Lima and colleagues from Brazil's National Institute for Space Research (INPE), the world's large dams emit 104 million metric tonnes of methane annually from reservoir surfaces, turbines, spillways and rivers downstream (1). This implies that dam methane emissions are responsible for at least 4% of the total warming impact of human activities. No one has yet calculated the total climate impact of dams, which would include releases of carbon dioxide and nitrous oxide
According to the estimates of the INPE researchers, dams are the largest single anthropogenic source of methane, being responsible for 23% of all methane emissions due to human activities. Methane is a much more potent heat-trapping gas than carbon dioxide, although it does not last as long in the atmosphere.
The most recent assessment of the Intergovernmental Panel on Climate Change states that methane has a warming impact 72 times higher than carbon dioxide if measured over 20 years, and 25 times higher measured over 100 years. Using these IPCC "global warming potential" (GWP) estimates means that one year's methane emissions from large dams, as estimated by Lima, have a global warming impact over 100 years equal to that of 2.6 billion tonnes of carbon dioxide. (Under the Kyoto Protocol, countries estimate their total warming impact using the 100 year GWPs). Over 20 years, the warming impact of annual large dam methane emissions is equivalent to 7.5 billion tonnes of carbon dioxide. By comparison:
Global CO2 emissions from fossil fuel burning (2004): 26.6 billion tonnes (2)
US CO2 emissions from fossil fuel burning (2005): 6 billion tonnes (3)
EU-15 emissions from fossil fuel burning (2003): 3.3 billion tonnes (4)
Global CO2 emissions from coal (2003): 9.6 billion tonnes (5)
US CO2 emissions from coal (2005): 2.1 billion tonnes (3)
US CO2 emissions from road transport (2005): 1.7 billion tonnes (3)
Global CO2 emissions from aviation (2002): 0.5 billion tonnes
According to the estimates of the INPE researchers, dams are the largest single anthropogenic source of methane, being responsible for 23% of all methane emissions due to human activities. Methane is a much more potent heat-trapping gas than carbon dioxide, although it does not last as long in the atmosphere.
The most recent assessment of the Intergovernmental Panel on Climate Change states that methane has a warming impact 72 times higher than carbon dioxide if measured over 20 years, and 25 times higher measured over 100 years. Using these IPCC "global warming potential" (GWP) estimates means that one year's methane emissions from large dams, as estimated by Lima, have a global warming impact over 100 years equal to that of 2.6 billion tonnes of carbon dioxide. (Under the Kyoto Protocol, countries estimate their total warming impact using the 100 year GWPs). Over 20 years, the warming impact of annual large dam methane emissions is equivalent to 7.5 billion tonnes of carbon dioxide. By comparison:
Global CO2 emissions from fossil fuel burning (2004): 26.6 billion tonnes (2)
US CO2 emissions from fossil fuel burning (2005): 6 billion tonnes (3)
EU-15 emissions from fossil fuel burning (2003): 3.3 billion tonnes (4)
Global CO2 emissions from coal (2003): 9.6 billion tonnes (5)
US CO2 emissions from coal (2005): 2.1 billion tonnes (3)
US CO2 emissions from road transport (2005): 1.7 billion tonnes (3)
Global CO2 emissions from aviation (2002): 0.5 billion tonnes
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