I wrote recently about some truly exciting developments in soil reclamation with enormous potential for agriculture. (See The Earth.) There is great news in much of this if we pay attention and give these low-tech, largely low-energy-intensive approaches the focus they deserve.
The (really) bad news is that although fertilizers have increased agricultural output over the years, they have also caused devastating environmental impacts. I have been remiss here in not addressing the harm that the increasingly pervasive use of fertilizers has had, not only on exacerbating global warming, but on creating "dead zones" in key marine areas.
Here is an important article today from the "NY Times" – Beyond Carbon: Scientists Worry About Nitrogen's Effects. It points out that public perception of the climate change crisis is mainly focused on the impacts from carbon dioxide and not on other greenhouse gases such as methane and nitrous oxide, both listed under the Kyoto Protocol as regulated GHGs. I would guess that the general public's lack of understanding of the impacts of these other GHGs is true. However, the Intergovernmental Panel on Climate Change, and scientists and policy analysts all over the world, fully recognize the dangers. The IPCC notes "Agriculture accounted for an estimated emission of 5.1 to 6.1 Gt carbon dioxide-eq/yr in 2005 (10-12% of total global anthropogenic emissions of greenhouse gases). Methane contributes 3.3 Gt carbon dioxide-eq/yr and nitrous oxide 2.8 Gt carbon dioxide-eq/yr. Of global anthropogenic emissions in 2005, agriculture accounts for about 60% of nitrous oxide and about 50% of methane." (See the chapter on Agriculture from the IPCC's Fourth Assessment Report, Working Group III.)
Notice that the IPCC, as others do, uses the measure "carbon dioxide-equivalent." The IPCC says carbon dioxide " is the reference gas against which other greenhouse gases are measured" So, in any event, methane and nitrous oxide are very much under scrutiny along with carbon dioxide, and three others, sulphur hexafluoride, hydrofluorocarbons, and perfluorocarbons, used in refrigeration and for other heavy industrial purposes. These last three are being phased out under Kyoto and the Montreal Protocol because they are potent ozone-depleting chemicals (ODCs) as well.
The "NY Times" points out that there is another potent GHG, nitrogen trifluoride, which is not regulated. It has been used in relatively small quantities but its use is increasing significantly. For what purpose is it used primarily? For making LCD panels.
Let's return to nitrogen fertilizers and nitrous oxide, with an output of nearly three billion tons a year of carbon dioxide equivalent. Greenpeace International had an excellent report out earlier this year – Cool Farming: Climate impacts of agriculture and mitigation potential. As they put it: "Nitrous oxide emissions are mainly associated with nitrogen fertilisers and manure applied to soils. Fertilisers are often applied in excess and not fully used by the crop plants, so that some of the surplus is lost as nitrous oxide to the atmosphere." This is a good, comprehensive report with some lucid explanations and some worthwhile graphics. They also have a good bit to say here about mitigation options, as does the IPCC, of course, in the document cited above. See also the International Nitrogen Initiative which is " dedicated to optimizing the use of nitrogen in food production, while minimizing the negative effects of nitrogen on human health and the environment as a result of food and energy production."
The "NY Times" article is careful to note that there are other concerns in play aside from the radiative forcing from nitrous oxide, not to mention the carbon dioxide and methane from agriculture. One of the most dire of these are the ocean dead zones that result from the pooling of millions of tons of nitrogen fertilizer runoff. NASA explains it this way: "The apparent cause of the creeping dead zones is agriculture, specifically fertilizer. While fertilizer is necessary to foster bumper agricultural crops, it also runs off the fields into the streams and rivers of a watershed. When the fertilizer reaches the ocean, it just becomes more nutrients for the phytoplankton, so they do what they do best: they grow and multiply. Which leads to more organic matter reaching the bottom, more bacterial respiration, and more anoxic bottom water." For some good graphic explanations of the phenomenon, try this from the Science Museum of Minnesota.
