I have a paper up on the Geoengineering Our Climate site about “nitrogen geoengineering”. It argues that there is at least a case for seeing the human takeover of the nitrogen cycle as an act of geoengineering, and that — to some extent independently of whether you accept that case — the nitrogen takeover has lessons for people with an interest in geoengineering the climate. Some of this material will end up in chapter six of my book (eventually..) though in rather different form (which makes it worth noting that , although this is not explicitly stated on the geoengineeringourclimate.com site, I retain the copyright.)
Some people (including one referee on the paper) have responded by saying that if industrial nitrogen fertilization counts as geoengineering, then so do various other agricultural innovations, and indeed agriculture itself. I can accept that there is perhaps a continuum here, but I think its worth noting that: the nitrogen revolution depends on a specific technological breakthrough which was actively sought due to scientific and political concern about a global problem; it was implemented not in a purely bottom up way but at least in part as an act of deliberate geopolitical policy (“the green revolution”); and it has had effects on the earth system that were global in their significance. To me this all marks it out as being more akin to a piece of geoengineering than anything that had gone before, and indeed anything since.
In what ways can this historical analogue inform debates about climate geoengineering? First, it offers an existence proof. It is possible for humans to identify a global problem, create a technology that addresses that problem, and deploy it on a global scale.
It also shows that the scope of such an intervention can greatly outstrip its progenitors’ plans, and perhaps their imaginations. While Sir William Crookes did not put specific numbers on the amount of nitrogen he felt was needed when he raised the issue as president of the British Association, the scale of today’s nitrogen industry and its effects surely far outstrips the consequences he expected. This suggests that those imagining possible futures for climate engineering should take care that they imagine applications of the technology well beyond the minimum that seems to be required—not as necessary endpoints to the programme, but as plausible ones.
There are other aspects of nitrogen geoengineering that climate geoengineers should be aware of. One is that it is deployed inefficiently. Most of the deliberately fixed nitrogen does not get into crops; Vaclav Smil estimates that the overall efficiency of the global food system seen this way is less than 15%. The wasted nitrogen is not just a loss; it often does harm. Over-fertilized soils produce nitrous oxide, which destroys stratospheric ozone and is also powerful greenhouse gas. Nitrate-bearing run-off waters from agricultural watersheds stimulate algal blooms and “dead zones” in coastal seas. While nitrogen fixation has made the world more habitable by humans—more precisely, habitable by more humans—than it could be in a state of nature, it has also done significant damage to biodiversity, human health and ecosystem services in the process.
As I said, the whole thing is here. Feedback welcome, as ever.
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