1%

More than one percent of all the energy used by humankind goes to synthesizing ammonia. Ammonia is used to make nitrogen fertilizers. The higher grain yields obtained with nitrogen fertilizer are absolutely necessary to feed more than 40% of the world's population, and to support the nitrogen-intense diet of the rest of the world.

Anthropogenic sources (primary ammonia synthesis, but also NOx from fossil fuel combustion and cultivation of leguminous crops such as soybeans) account for well over half of the flux of nitrogen fixation in the world (on land). This is a huge perturbation to the global geochemical cycling on nitrogen. Biogeochemists, however, haven't yet figured out what happens to all the nitrogen fertilizers we put in the ground. Some of it forms nitrates which enter groundwater via leaching from the soil or runoff into lakes and rivers. No one knows what happens to all the nitrate after that, though. Either it is "denitrified" by soil and freshwater microorganisms, or it is being trapped in some unknown and huge nitrate reservoir, possibly deep underground.

The full environmental consequences of all this extra nitrogen are largely unknown.