Abstract:The present study aimed to reveal historical trends and distribution patterns of enteric methane (CH4) emissions from ruminants in China between 1990 and 2010. Enteric CH4 emissions were calculated using the Tier 1 equation provided by the Intergovernmental Panel on Climate Change (IPCC). The enteric CH4 emission factors of different ruminant subcategories were the corresponding default values provided by the IPCC (2006), such as 61 kg CH4 head-1 a-1 for dairy cows, 47 kg CH4 head-1 a-1 for both beef and draught cattle, and 5 kg CH4 head-1 a-1 for both sheep and goats. In addition, information about the population size of cattle, dairy cows, goats, and sheep was obtained from the Statistical Yearbook of China and Statistical Yearbook of China's animal husbandry. The enteric CH4 emissions in each province were also estimated to obtain the distribution pattern of national enteric CH4 emissions from 1990 to 2010. The results showed that the total enteric CH4 emissions of ruminants ranged from 5.90 to 7.65 Tg, with the maximum value being obtained in 1995. The enteric CH4 emissions from beef and draught cattle (mainly cattle and buffalo) exceeded 4.33 Tg, accounting for more than 65% of total enteric CH4 emissions. The enteric CH4 emissions from dairy cows showed a continuous rising trend with advancing years. In 2006, the amount and proportion of enteric CH4 emissions from dairy cows (0.83 Tg, 12.7%) exceeded that detected from goats and sheep, and represented the second largest source of enteric CH4 emissions in the ruminant production system. However, enteric CH4 emissions per kg of milk production decreased, indicating that the efficiency of dairy farming had greatly improved from 1990 to 2010. The distribution pattern of the enteric CH4 emissions showed regional variation, and was mainly distributed in the northern, western, and central regions of China. For example, 10 provinces (including Sichuan, Inner Mongolia, Xinjiang, Henan, Tibet, Shandong, Hebei, Heilongjiang, Yunnan, and Gansu) accounted for more than 50% of total enteric CH4 emissions. The distribution pattern of the enteric CH4 emissions of ruminant subcategories also exhibited regional variation. The enteric CH4 emissions of beef and draught cattle were mainly distributed in the southwest and central regions of China, with 10 provinces (including Sichuan, Yunnan, Guangxi, Guizhou, Henan, Shandong, Hunan, Hebei, Tibet, and Anhui) in China accounting for more than 55% of total enteric CH4 emissions by these ruminants. The enteric CH4 emissions of dairy cows were mainly distributed in the northern regions of China, with six provinces (including Xinjiang, Inner Mongolia, Heilongjiang, Henan, Hebei, and Shandong) in China accounting for more than 55% of total enteric CH4 emissions by this group. The enteric CH4 emissions of goats were mainly distributed in the northern and central regions of China, with five provinces (including Inner Mongolia, Shandong, Sichuan, Henan, and Jiangsu) in China accounting for more than 50% of total enteric CH4 emissions by this group. The enteric CH4 emissions of sheep were mainly distributed in the northwest regions of China, with five provinces (including Xinjiang, Inner Mongolia, Tibet, Qinghai, and Gansu) in China accounting for more than 60% of total enteric CH4 emissions by this group. In summary, ruminants represented (6.77 ± 0.46) Tg (of which more than 65% was from beef and draught cattle) of national enteric CH4 emissions from 1990 to 2010, which initially increased and then decreased with advancing years. The distribution pattern of national enteric CH4 emissions exhibited regional variation, with 60% of total enteric CH4 emissions originating from the northern, western, and central regions of China.