Discussions of climate geoengineering often treat it as an unprecedented venture. James Fleming's perspective in the preceding piece as well as his previous writing on the history of weather modification clearly show that this is not the case; people have been discussing manipulations of weather and climate, and developing technologies to that end, for a long time. The 20th century's development of nitrogen geoengineering is the most dramatic example history provides of humans changing the way the Earth system works. The nitrogen cycle, no less than the carbon cycle, is fundamental to the way the Earth's biosphere works. The bacteria that "fix" nitrogen from its inert gaseous form into compounds that can be made use of by plants, and the animals that eat them, are a key part of this cycle. There are other aspects of nitrogen geoengineering that climate geoengineers should be aware of. One is that it is deployed inefficiently.