Things I've Learnt About Agricultural Greenhouse Gas Emissions

While on holiday on in Nelson I engaged in some blogging back and forth with Charles Finny at Dear John on the subject of agricultural greenhouse gas emissions and Kyoto.

Since then I have been trying to get up to speed on some of the questions we discussed so as to reach a non-holiday, informed, opinion on the issues.

One good resource for information is the UN Food and Agriculture Organisation's 2006 report Livestock's Long Shadow. Despite being a product of the dreaded UN, and one that has come in for some political criticism, this seems to me a generally informative and well referenced report. In particular Chapter 3 addresses agriculture's impact on the carbon cycle.

Firstly: we spent some time on arithmetic. Charles wanted to estimate the savings if agricultural methane emissions were discounted under the assumption that every atom of carbon in emitted methane originated from grass that had recently absorbed CO2 from the atmosphere due to photosynthesis. This resulted in a reduction in CO2 equivalent emissions equal to about 10% of agricultural methane emissions.

Whatever the merits of the premise I would argue that this shows that New Zealand policy makers should pay very close attention to the provisions related to agriculture in any Kyoto successor with a view to improvements that could also constitute significant savings to the New Zealand taxpayer. And it goes without saying that more attention could probably have been paid in the negotiation of the original treaty.

Finally on this point I'll just mention that Kyoto apparently regards the CO2 emissions from livestock respiration as being offset by the CO2 absorption of the grass they eat but charges in full for methane emissions from enteric fermentation and the decomposition of dung. This is addressed in section 3.2.2 of the report.

That said, I still don't know what is wrong with the argument that every C atom in CH4 emitted by livestock also originated in CO2 recently absorbed by the grass they ate.

Secondly: this discussion assumed farming was going on in a steady state. The report highlights the fact that land use changes, in particular cutting down forests for agriculture, result in much of the carbon emissions related to agriculture. Deforestation in New Zealand in favour of dairy farming has been a significant source of carbon emissions as we all know.

Thirdly: on a related point we also ignored the fact that farm land, like forests, can be significant carbon sink and the stored carbon can be increased by appropriate farming practices. It's estimated that one quarter of the international response to climate change could involve storing carbon on land (terrestrial carbon sequestration). Of this it seems that about a third could be carbon storage in agricultural land rather than new forests or avoided deforestation. (For information about this you should take a look at the recent Lowy Institute talk by Ralph Ashton, video here and podcast from the Lowy Institute.)

Typically the conversion of natural ecosystems to agriculture results in the loss of 20 to 50% of the stored organic carbon in the top metre of soil. However there is evidence that at least 50% of this lost carbon storage can be restored by appropriate farming practices. These include agricultural intsensification, conservation tillage and erosion reduction. This is discussed in section 3.5.1 of the FAO report. It seems that Professor Rattan Lal at the University of Ohio is at least one of the world experts on this and those of you with access to a Science subscription may be interested in his review article on soil carbon sequestrtion, global warming and food security.

The hook here is that, unlike sequestration in forests, avoided deforestation and agricultural sequestration are not included in Kyoto. So while they have a positive effect on climate change they do not contribute to a nation's responsibilities under Kyoto. A high level group the Terrestrial Carbon Group, which includes Nobel Prize winning economist Joseph Stiglitz and Australian environmental scientist Tim Flannery, have a proposal for how to fix this in any Kyoto successor. This proposal is discussed in Ashton's talk.

Surely if the New Zealand government wishes to put flesh on the bones of its statement at Poznan it should be advocating for efforts like this and in particular a fuller accounting of agricultural emissions and carbon storage?