Barker noted that raising animals for food is one of the largest sources of carbon dioxide and the single largest source of both methane and nitrous oxide emissions.
巴克提到饲养动物作为食物是二氧化碳的一种主要来源，并且是甲烷和氧化亚氮排放的唯一主要来源。
2
He and some of his grad students wanted to use nitrous oxide as an emissions-free energy source.
他和他班上一些大学生想利用氧化氮作为无排放的动力能源。
3
When summed across the globe, the results showed rivers and streams are the source of at least 10 percent of human-caused nitrous oxide emissions to the atmosphere.