Nothing affects global food security as much as synthetic nitrogen fertiliser. Nothing underlines the inadequacy of organic farming for meeting current food and feed demand while sparing forests as much as the global accounts on the nitrogen cycle that is an essential part of all life on the planet.
These facts of life are captured succinctly by an image available at The Economist website this week in their essay on the Anthropocene.
The Anthropocene: A man-made world | The Economist: “May 26th 2011 | from the print edition”
Science is recognising humans as a geological force to be reckoned with…
…The [Nitrogen] fix is in
No Dickensian insights are necessary to appreciate the scale of human intervention in the nitrogen cycle. One crucial part of this cycle—the fixing of pure nitrogen from the atmosphere into useful nitrogen-containing chemicals—depends more or less entirely on living things (lightning helps a bit). And the living things doing most of that work are now people (see chart). By adding industrial clout to the efforts of the microbes that used to do the job single-handed, humans have increased the annual amount of nitrogen fixed on land by more than 150%. Some of this is accidental. Burning fossil fuels tends to oxidise nitrogen at the same time. The majority is done on purpose, mostly to make fertilisers. This has a variety of unwholesome consequences, most importantly the increasing number of coastal “dead zones” caused by algal blooms feeding on fertiliser-rich run-off waters.
Industrial nitrogen’s greatest environmental impact, though, is to increase the number of people. Although nitrogen fixation is not just a gift of life—it has been estimated that 100m people were killed by explosives made with industrially fixed nitrogen in the 20th century’s wars—its net effect has been to allow a huge growth in population. About 40% of the nitrogen in the protein that humans eat today got into that food by way of artificial fertiliser. There would be nowhere near as many people doing all sorts of other things to the planet if humans had not sped the nitrogen cycle up.
It is also worth noting that unlike many of humanity’s other effects on the planet, the remaking of the nitrogen cycle was deliberate. In the late 19th century scientists diagnosed a shortage of nitrogen as a planet-wide problem. Knowing that natural processes would not improve the supply, they invented an artificial one, the Haber process, that could make up the difference. It was, says Mark Sutton of the Centre for Ecology and Hydrology in Edinburgh, the first serious human attempt at geoengineering the planet to bring about a desired goal. The scale of its success outstripped the imaginings of its instigators. So did the scale of its unintended consequences.
For many of those promoting the idea of the Anthropocene, further geoengineering may now be in order, this time on the carbon front. Left to themselves, carbon-dioxide levels in the atmosphere are expected to remain high for 1,000 years—more, if emissions continue to go up through this century. It is increasingly common to hear climate scientists arguing that this means things should not be left to themselves—that the goal of the 21st century should be not just to stop the amount of carbon in the atmosphere increasing, but to start actively decreasing it. This might be done in part by growing forests (see article) and enriching soils, but it might also need more high-tech interventions, such as burning newly grown plant matter in power stations and pumping the resulting carbon dioxide into aquifers below the surface, or scrubbing the air with newly contrived chemical-engineering plants, or intervening in ocean chemistry in ways that would increase the sea’s appetite for the air’s carbon….continues at the Economist