New Zealands biogenic methane emissions and the not zero target

In the recently unveiled Zero Carbon Bill, or more correctly, the Climate Change Response (Zero Carbon) Amendment Bill, biogenic methane emissions get a separate and distinctly non-zero emissions reduction target.

What are these methane emissions? I thought I would do some graphical analysis.

First of all - definitions. The draft bill in Section 4 amended (Interpretation) defines biogenic methane as:

"...all methane greenhouse gases produced from the agriculture and waste sectors (as those sectors are defined in the New Zealand Greenhouse Gas Inventory)".

The New Zealand annual greenhouse gas inventory records three sub-categories of methane; methane from enteric rumination, methane from agricultural soils and methane from the waste sector. Waste sector emissions in 2017 were 95% methane, 4.12475 million tonnes and 5% of total gross emissions. That's a significant chunk of New Zealand's GHG emissions.

Why is the waste sector methane included? It's not sourced from agriculture. None of the advocates of the split-gas target, like David Frame or Simon Upton, made any arguments about waste sector methane. Also, the Productivity Commission in it's 2018 report Low Emissions Economy thought waste sector emissions could be feasibly reduced. (See page 451 of their final report; "Waste also represents a major mitigation opportunity.")

The methane from enteric rumination, from agricultural soils and from the waste sector and the total biogenic methane look like this.

The total biogenic methane emissions in 2017 was 40.34134 million tonnes. It's a crude point so here's a crude pie graph to make it, 40 million tonnes of biogenic methane is half of gross emissions (excluding landuse and forestry).

40 million tonnes of biogenic methane is more than twice the quantity of net emissions (including landuse and forestry). Net emissions are 41% of biogenic methane emissions.

This line graph shows how the biogenic methane emissions compare to gross and net emissions over the 1990 to 2017 period. In the early 1990s, biogenic methane emissions exceeded net emissions.

The amount of biogenic methane emissions exceeds all emissions attributed to the agricultural sector. So the 'split' gross target, in carbon dioxide equivalents, is less than a counterfactual target where all agricultural sector emissions are excluded.

For context, here is my preferred graph of all New Zealand's greenhouse gas emissions by sector.

This next graph below shows actual emissions and the split gas targets; biogenic methane to 10% less by 2030, and to either 24% to 47% less than 2017 by 2050.

Net emissions in carbon dioxide equivalents, after taking out methane, go to...well..zero of course in 2050. I have assumed that carbon sequestration from the land use and forestry sector is the same in 2050 as it was in 2017.

Note that from 1990 to 1995, the net emissions were less than the 2050 net zero carbon dioxide target. In other words, under the net zero split gas carbon dioxide/methane targets definition, New Zealand's greenhouse gas emissions were negative. Can anyone credibly argue that New Zealand's greenhouse gas emissions in the early 1990s were 'net zero'?

Now this final graph shows the targets scaled up to include gross emissions as well as net. Gross emissions must decline at the same rate as net emissions. As the difference between them is the carbon sequestration from land use and forests.

The key point here is that if the sequestration in 2050 is about 23 million tonnes (the same as in 2017) then the New Zealand 'net zero' target for gross emissions, is 50 million tonnes. That's still a heck of a lot of emissions.

The net zero/split gas target is not nearly as stringent as all the pundits seem to think. It is hard not to conclude that the waste sector methane has been moved to the less stringent methane target in order to make the carbon dioxide target larger in 2050 and therefore easier to achieve. This, unfortunately, seems to be another example of New Zealand's favourite climate change practice; achieving targets by creative accounting instead of reducing emissions.