The breakdown of cellulose occurs in the stomachs of cattle. This links the production of methane gas (CH₄) to food production (meat and milk). Decay of dead organic material also produces methane gas. This occurs in bogs and marshes, where murky water pools and harbors many microorganisms that break down dead plant material in the marsh.

Rice paddies are essentially marshes, so anthropogenic CH₄ is produced by this agricultural practice. For other food crops, the decomposition of unharvested, waste plant material produces methane. All this means is that as world population increases, the increased food production results in increased CH₄ emissions (and probably higher CO₂ concentration as well, from the deforestation needed to support this food production). This makes it difficult to regulate CH₄ emissions, because there are few practical substitutes to large-scale food production.

Nitrous oxide (N₂O) emissions can be linked to agriculture just like CH₄, except now it's more widespread---it applies to just about anything grown in soil. Soil bacteria, often living on the roots of plants (legumes, such as beans, in particular) eat nitrate compounds in the soil and convert them to N₂O. In commercial agriculture, fertilizers (including that old standby, steer manure) contain nitrates (helps the plant produce leafy green mass). Much of the recent sudden increase in N₂O emissions can be attributed to the use of the nitrate fertilizers.

As with CH₄, regulation of N₂O emissions will be difficult because without the nitrate fertilizers, the productivity of agricultural lands may be too low to sustain the food production needed by the large global population. Note that growing vegetables organically does not significantly reduce the output of N₂O--organic fertilizers are still supply the same nitrate nutrients as chemical fertilizers, and vigorously growing plants will result in the same N₂O emissions no matter what the nitrogen source, since it's all chemicals to plants anyway.

All chlorofluorocarbons (CFCs) are anthropogenic (except for a few similar compounds that are not really true CFCs). Their long atmospheric lifetimes (50-100 years) pose a potential problem, in that it allows the concentration to build up before breakdown in the stratosphere can remove them (and then there is a whole new set of problems from CFC breakdown in the stratosphere).

Modern countries like the U.S. have agreed to limit and reduce the amount of CFCs manufactured and emitted to the atmosphere, so the problem should take care of itself over time. Unfortunately, developing countries are just now showing capacity to manufacture and/or use these materials (for refrigeration, mostly), so in the near future, there may still be a ramping-up of CFC concentration as these materials are used in these regions. [One can suppose that in the absence of practical substitutes, CFCs are linked to a necessity of modern life---refrigeration---and like the gases that are linked to food production, it will be difficult to regulate something that is essential to food, in this case preservation.]