FUTURE METHANE EMISSIONS FROM ANIMALS

The future global emission of CH4 from enteric fermentation in animals has been estimated for cattle, sheep, and buffalo, which together contribute approximately 91% of the total CH4 emitted from domesticated animals at present. A simple model has been used to relate livestock levels to the national human populations for each country involved in breeding the three species included in this analysis. United Nations population predictions to 2025 were then included in the model to estimate future CH4 emissions. A variational analysis was carried out to investigate the effect of future changes in both the land available for grazing and the nutritional content of feedstocks. Results suggest that the total emission of CH4 from enteric fermentation in domestic animals will increase from 84 Tg CH4 per year (Tg = 10(12) g) in 1990 to 119 (+/- 12) Tg CH4 yr-1 by 2025. These values correspond to an average rate of increase over the next 35 years of 1.0 Tg CH4 yr-1.