Actually, the atmospheric concentration of methane and CO2 are increasing with an alarming rate. But I confused regarding ambient methane concentration. It is known to me up to 90% methane converted to CO2. Is it really happen after emission of methane in atmosphere or before emitting in atmosphere?
Dr Islam, part of the methane produced in the rice soil is consumed in the oxidized rhizosphere of rice roots or in the oxidized soil-flood water interface. Therefore, reduction in soil methane does not necessarily reflected that all these CH4 emitted into the atmosphere. As conversion of methane to CO2 needs oxygen so it mostly happen after emission of methane in the atmosphere . Enclosed please find some interesting related works.
Thanks Dr. Tarafdar for your information and related supporting. You mentioned CH4 is consumed in the rice oxidized rhizosphere and converted to CO2 after emitting into the atmosphere. I completely agree with you, but my query is all produced methane converted to CO2?
Thanks Dr. Tarafdar. Now we have to address remaining 20% methane only from agriculture. Because 80 % methane converted to CO2. We know CO2 balance almost zero in agriculture. So, Emission of CH4 is not a significant factor in agriculture?. In contrast, N2O emission is negligible in continuous flooded rice culture. On the whole, GHG emission in agriculture is not a big issue?
Dear Colleague, I am not sure the answers provided above tell all the story. The methane emitted in rice fields into the atmosphere converts entirely to CO2 enentually... However during its lifetime, which is in the order of 10-20 yrs on average, it has a very high impact on climate forcing. Taking a hundred years window, the forcing of a kg of methane emissions into the atmosphere is 20-30 times bigger than a kg CO2 emitted the same way.... This measure is called a global warming potential (GWP), and to be precise, developing countries used a GWP value of 21 for methane, when compiling their GHG inventories, according to the current UNFCCC guidelines. So, the problem is not the overall carbon mass balance, since in fact from a CO2 perspective only, the emissions would appear to be carbon neutral (the final CO2 from the methane would have been fixed by photosynthesis). However it is not. The problem should be viewed in terms of warming impact of the methane emissions. From this standpoint, which is all that it matters here, methane has a large overall effect on climate forcing, and this cannot be canceled out by a simple carbon mass balance. This is why climate impact is to be measured in terms of CO2eq and not CO2 only. If you look at available databases, for instance the one we maintain at FAO on GHG ag emissions (http://www.fao.org/faostat/en/#data/GT/visualize), you will see that the yearly impact of global CH4 emissions from rice is about 500 million t CO2eq yr-1 (This is about 20% of all the methane emitted annually by agriculture; The main contributor being enteric fermentation from ruminant livestock). My take home point is: in terms of global warming, 100% of the emitted anthropogenic methane is the problem and needs to be considered in terms of mitigation. Best Regards, Francesco
I would like each of you to address the following:
CO2 is plant food. CO2 is actively pumped into greenhouses by burning either methane or propane to promote plant growth. Greening of the earth is promoted with increased CO2. Increasing leaf coverage and stimulating photosynthesis ultimately leads to cooling of the atmosphere especially in semi-arid envirotments because the stomata in leaves don't have to be opened as wide when CO2 levels are relatively high (400-1200 ppm) so less water is lost.during photosynthesis. Greenhouse gases have not predicted temperature rises well, I think because cloud formation effects are not well accounted for and because fluctuations of solar radiance are poorly predictable. Increased temperatures over oceans during spring and summer increases water vapor in the atmosphere, which leads to cloud formation and cooling. I think we should not be worried about increased CO2 levels, especially in agricultural and semi-arid regions. I think we should be focusing instead on decreasing nitric acid, sulfuric acid, carcinogenic hydrocarbons, and particulates, especially in areas where inversions are common by getting rid of combustion engines and using more electric powered cars and getting rid of sulfur in fossil fuels like coal and oil.
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