Radiative forcing of Earth's atmosphere is increasing at unprecedented rates, largely because of increases in the concentrations of atmospheric trace gases, mainly carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) - collectively known as greenhouse gases (GHG). Concentrations of CO2, CH4 and N2O have increased markedly as a result of human activities since 1750 and now far exceeded pre-industrial values as determined from ice cores spanning thousands of years (Table 15.1). The atmospheric concentrations of CO2 and CH4 in 2005 have exceeded the natural range over the last 650,000 years (IPCC 2007). The global atmospheric concentration of CO2 has increased at an annual growth rate of 0.5%, while that of CH4 at 0.6% and nitrous oxide at 0.25%. Agriculture plays a major role in the global fluxes of each of these gases and is considered as one of the major anthropogenic sources (Fig. 15.1). Agriculture comprises several activities, contributing to GHG emissions and globally, the most significant activities identified include (i) deforestation and other land-use changes as a source of CO2, (ii) rice-based production systems (including rice-wheat rotation) as sources of CH4 and N2O (and also source of CO2 due to burning of agricultural residues) and (iii) animal husbandry as a source of CH4.
With an estimated global emission of non-CO2 GHGs over 5969 Mt CO2yr-1 in 2005, agriculture is estimated to account for about 14% of total global anthropogenic emissions of GHGs and 47 and 84% of total anthropogenic CH4 and N2O emissions, respectively (US-EPA 2006). CH4 emission from enteric fermentation and N2O emission from soils constitute the largest sources, accounting for 44 and
Central Rice Research Institute, Cuttack - 753006, Orissa, India e-mail: [email protected]
S.N. Singh (ed.), Climate Change and Crops, Environmental Science and Engineering, DOI 10.1007/978-3-540-88246-6.15. © Springer-Verlag Berlin Heidelberg 2009
Table 15.1 Major anthropogenic greenhouses from agriculture and their properties
Current tropospheric concentration (ppmV)
Atmospheric life time
GWP (100 years time horizon)
Increased radiative forcing (W.m2)
Carbon dioxide (CO2) 280 379 Variable 1
Methane (CH4) 0.715 1.774 12 23
Nitrous oxide (N2O) 0.270 0.319 114 296
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