Livestock impact on global emissions

However, his claims about the effects on global warming of livestock emissions are far from settled science.

Reisinger mentions that almost half New Zealand’s emissions come from livestock. Two-thirds of these are deemed to be methane. This is only true if the assumptions underlying the calculations are true. 

Different greenhouse gases cause differing amounts of warming. To compare one gas with another, all are converted to ‘carbon dioxide equivalents’. But there is no one particular way to do this. The chosen method is one known as ‘global warming potential’. An alternative method is ‘global temperature change potential’. This method would reduce our methane emissions to a third of their current level.

Furthermore, the calculations count all the emissions from our livestock each year. Methane does not last long in the atmosphere. This means that a constant number of livestock will have methane breaking down as fast as they produce it and the atmospheric concentration does not change. 

Global warming cannot occur unless there is an increase in greenhouse gas concentration. The IPCC in its most recent report, the AR5, considers that the methane produced at any given point in time is effectively gone after 50 years. That suggests that our methane emissions from 50 years ago should be deducted from the current figure to give the net amount.

Reisinger claims reducing livestock emissions from livestock can help stop the world warming more than 2^oC. But I have just pointed out that the major livestock emission, methane, is gone in 50 years so the temperature in 50 years will be no different whether we produce the methane or whether we don’t.

But the real heart of the matter is just how much warming our livestock emissions produce in the first place. In spite of tomes of literature – such as the UNFAO’s ‘Livestock’s Long Shadow’ – it appears no one has quantified this. I have yet to find a scientist who can give a figure off the cuff, in spite of a paper by Scottish chemist Dr Wilson Flood, which shows that a doubling of methane from all sources would raise temperature by a mere 0.07^oC, without allowing for feedbacks, which is yet another contentious issue that is beyond the scope of this item. With feedbacks it would be 0.21^oC. Even Dr Reisinger’s own pastoral Greenhouse Gas Research Consortium (PGGRC) had to reach for the calculator to answer my request for a figure. 

Of the various figures I have from different sources, the PGGRC’s is the highest at 0.2^oC for livestock only, which is similar to the figure Dr Flood has from all sources. Someone has to be wrong. 

The PGGRC uses figures for methane forcings in their calculation that are more than double those listed in the IPCC’s AR5. No allowance is made for the carbon dioxide removed from the atmosphere to make the methane. Adjusting their figures for the above reduces the figure to 0.05^oC, which is entirely consistent with Dr Flood’s. My challenge to the PGGRC about their choice of figures received no response.

The PGGRC has previously stated it hopes to reduce livestock methane by 10%. That would reduce global warming by 0.005^oC. Who is prepared to pay a ‘carbon price’ of some form on their livestock to meet their share of this un-measurable amount?

NB. Dr Flood has read this and says he is in agreement with my arguments.

• East Coast farmer Neil Henderson has been actively involved in the issue of global warming since 2008, spending 2000-3000 hours doing research.