In a recent column, I summarized recent data from the 2020 Canadian submission to the United Nations Framework Convention on Climate Change (UNFCCC). The  data show Canadian and Canadian agricultural greenhouse gas (GHG) emissions for 2018, expressed in carbon dioxide (CO2) equivalents, are essentially unchanged from 2005. Year 2005 is the base year for reduction commitments made under the United Nation’s ‘Paris Accord.’

This newer column, based on improved calculation methodology, shows that a more accurate consideration of the relatively short atmospheric life of methane means both Canadian and Canadian agricultural emissions, measured as CO2-equivalent global warming potential (GWP), have actually plummeted since 2005. This should have major significance for future policy setting. The explanation follows.

First, a quick review of the earlier article, highlights of which are summarized in Table 1.

Table 1: Canadian and Canadian agricultural GHG emissions including credits and debits for LULUCF, on-farm fuel usage and Canadian biofuel consumption.

	2005	2018	2018/2005	% of Cdn total
	Mt CO2 equivalent		%	(2018)
Total Canadian gross emissions	730	729	100	100
LULUCF (sinks), Canadian total	-13	-13	100
Canadian net emissions including LULUCF	717	716	100
Agriculture
Ruminant digestion, CH4	31	24
Manure management, CH4 and N2O	9	8
N2O from soil fertilizing, management	19	25
Other	1	3
Agriculture total, reported to UNFCCC	60	59	98	8.1
Agricultural LULUCF (sinks)	-10	-6
Agricultural net including LULUCF	50	53	106	7.4
Add biofuel credit	-1	-6
Add on-farm fossil fuel usage	12	14
Agriculture total, biofuel and farm fuel included	61	61	100	8.5

The table presents statistics on Canadian GHG emissions for the years 2005 and 2018, with 2018 representing the most recent year for which official data are available. The values are expressed as ‘CO2 equivalents’ as defined by UNFCCC, recognizing that some GHG have a far greater climatic warming effect than CO2. The conversion factors used by UNFCCC for submissions for year 2018 are x25 for methane (CH4) and x298 for nitrous oxide (N2O). These values are their calculated average warming effects compared to CO2 over the 100-year period following emission. Note that the conversion factor for methane has recently been restated as x28, and even higher in recent publications from the International Panel on Climate Change (IPCC), but I’ll use x25 here as that’s the value used in the reports to UNFCCC.

Reports to UNFCCC also include emissions associated with storage or release of carbon dioxide from forests and soils – commonly referred to as either carbon sinks (presented as negative values) or sources (positive values). This overall category is called Land Use, Land Use Changes and Forestry, or LULUCF for short. Table 1 shows Canadian GHG emissions, either gross, or net after including LULUCF amounts.

Table 1 shows GHG emissions reported  to UNFCCC for Canadian agriculture. These values mostly involve GHG emissions associated with animal agriculture and various soil amendments (mostly manure, fertilizer and lime). The table also shows LULUCF changes that are the result of changing farm soil management practices and shifts of land into and out of agricultural crop production. Agricultural GHG emissions reported to UNFCCC consist primarily of CH4 and N2O, along with some CO2. The data for agriculture reported to UNFCCC do not include CO2 released in fossil fuel consumption for agricultural operations nor the reduction in Canadian CO2 emissions associated with biofuels. However, data are provided elsewhere in the submission to UNFCCC that permit these values to be calculated. I’ve done this in the final three lines of Table 1.

Table 1 permits two general conclusions:

• Canadian and Canadian agricultural GHG emissions, whether including LULUCF or not, changed hardly at all from 2005 to 2018.
• There was a shift In Canadian agriculture to more emissions from N2O and less from CH4 over this 13-year interval, but the sum of all agricultural emissions remained at about 8% of total Canadian emissions.

In recent years, there has been intensive debate on whether the UNFCCC reporting methodology, based on protocols prescribed by the International Panel on Climate Change (IPCC), provides an accurate estimate of expected global warming for emissions of certain GHG, especially methane.

Methane has a comparatively short life span in the atmosphere before being converted into CO2 and water. With a half-life of about 12 years, only about 1/16 of an originally emitted amount of CH4 will remain in atmosphere after 50 years; yet the IPCC calculation assumes continued presence for another 50 years to follow. Of course, the offset is that methane has an atmospheric warming potential of about x84 for the initial few years – that’s how the 100-year average of x25 arises – and that must be accounted for in calculations too.

With continuing CH4 emissions of constant magnitude, the atmospheric concentration will level off after a number of decades as rate of decomposition proceeds as quickly as rate of addition. And if the rate of CH4 emission declines, the atmospheric warming potential declines within a relatively few years as well – notwithstanding the current UNFCCC protocol that assumes otherwise.

It’s true that most other GHG also dissipate in the atmospheric with time, but at a far slower rate than methane. In the case of CO2, dissipation occurs because of photosynthesis-less-respiration, net storage of CO2 in carbon sinks, and absorption by oceans. This takes many decades and even centuries. The atmospheric half-life for N2O is more than 100 years.

There are numerous recent publications that describe this subject more completely. In particular, I refer readers to this recent overview by Dr. Frank Mitloehner and his colleagues at the University of California-Davis.

More detail is provide in a series of publications by Drs. Michelle Cain, John Lynch, Myles Allen and colleagues at the University of Oxford. A brief overview is here; a more-detailed but very readable report is here; the full scientific/statistical analysis is here.

The Oxford University team has created a measure called the GWP* (GWP-star, also called CO2 warming equivalent, or CO2_we) which is a more accurate estimate of the Global Warming Potential of methane over a 100-year interval.  The calculation involves two components, the first reflecting the large but short-term, initial warming effect, and a smaller second term that is the longer-term effect. GWP* is calculated as follows:

GWP* (CO2_we ) = ((r x ΔCH4/Δt x 100 years) + s x CH4)  x CO2₁₀₀,

where, CO2_we = ‘warming equivalent’ compared to CO2;  r and s are two constants derived statistically, with r + s = 1.00; ΔCH4 = change in annual methane emissions; Δt = number of years over which this change occurred; CH4 = methane emissions in current year; CO2₁₀₀ = 100-year CO2-equivalent conversion factor for methane as defined by IPCC (i.e., 25).

While the Δt interval can be any number of years in this equation, the Oxford team has recommended 20 years as most appropriate and have calculated r and s values of 0.25 and 0.75 for the 20-year duration.

In Table 2, I have recalculated the principal values in Table 1, replacing the originally x25-transformed values for methane with GWP*.

Table 2: Canadian and Canadian agricultural GHG using GWP* for methane emissions.

	2005	2018	2018/2005	% of Cdn total
	Mt CO2 equivalent		%	(2018)
Total Canadian gross emissions	703	592	84	100
LULUCF (sinks), Canadian total	-13	-13
Canadian net emissions including LULUCF	693	579	84
Agriculture
Agriculture gross	64	29	45	4.9
Agricultural LULUCF (sinks)	-10	-6
Agricultural net including LULUCF	54	23	43	4.0
Add biofuel credit	-1	-6
Add on-farm fossil fuel usage	12	14
Agriculture total, biofuel and farm fuel included	66	31	47	5.4

The base data on Canadian and Canadian agricultural emissions of methane come from annual National Inventory Reports to UNFCCC by Canada for the years 1990 through 2018 (see following graph).

A few explanations are needed regarding calculations used to create Table 2:

• GWP* calculations require data on annual methane release for the current year and that 20 years earlier. This presents a problem for 2005 calculations in that Canadian UNFCCC data are only available for years 1990 to 2018. For agriculture, a close linear relationship exists for those years between annual methane emissions reported to UNFCCC and total Canadian cattle numbers published by Statistics Canada. Hence, I was able to estimate Canadian agricultural methane emissions using the cattle number for 1985. (The number for 1985 is about 5% higher than for 1990.) Unfortunately, I was not able to find something comparable for total methane emissions for Canada, so I assumed the 1985 number to be the same as for 1990. That may represent an over-estimate for 1985 (Canadian methane emissions trended upward from 1990 to 1995) and, hence, an underestimate in the true change in Canadian methane emissions that occurred from 1985 to 2005.
• The LULUCF emissions include a small emission of methane. However, it is generally less than 1% of the equivalent value for Agriculture, and too small to be of meaningful significance. I ignored LULUCF-GWP* values in producing Table 2.
• There are three dominant sources of methane emissions in Canada – losses associated with natural gas, methane from waste management, and ruminant animals. The Canadian ruminant animal source (primarily cattle) increased from 1987 to 2005 but has steadily declined since then. Total Canadian methane emissions increased until the year 2000 and have declined since then (down by 18% from 2000 to 2018). Because of this, calculated values for GWP* for 2018 for methane are actually negative for both Canada and Canadian agriculture.

Negative values for GWP* when methane emissions are declining is fully consistent with the GWP* concept as shown in the following series of graphs from Dr. Cain of the Oxford team:

When methane emissions are increasing with time, the global warming effect of methane also increases. When the methane emission rate is constant, the global warming effect is static (unlike CO2 where continued CO2 accumulation means increased warming). But when methane emission rate declines – as for both Canada and Canadian agriculture after 2005 – the warming effect of methane declines. And that’s what’s evident in Table 2.

Some key conclusions from Table 2 are:

• The global warming potential (GWP) of Canadian GHG emissions has declined by about 20% since 2005 when the warming effect of methane emissions is calculated more accurately.
• The calculated GHG global warming potential for Canadian agricultural emissions has declined by more than 50% since 2005.
• Canadian agriculture (2018) represents only about 5% of total Canadian GHG global warming potential.
• The decline in methane emissions since the early 2000s actually means a cooling effect. Even if Canadian cattle numbers change little in the next few years, the cooling effect caused by reductions in ruminant methane emissions since 2005 will continue – for about another 14 years according to my calculation using the Oxford equation.

I also did a calculation of what the difference would be over the interval 2019 to 2050 if Canadian agricultural emissions were to remain the same every year as in 2018. I calculated, using the Oxford equation, that use of GWP* for converting methane emissions into CO2_we over that 32-year interval would mean a 45% reduction in total accumulated atmospheric warming potential for GHG emissions from Canadian agriculture – compared to that calculated using x25 .

One caution: Readers should treat the numbers shown in Table 2 as approximations only. I have no idea of the size of the error of estimate. But even if the results are only rough approximations, this calculation procedure, based on sound science, does represent a major improvement over the calculation procedure for methane now used for UNFCCC submissions, and the trends shown in Table 2 seem very significant.

How the global warming effect of methane is calculated should mean a huge difference in strategic planning on how to reduce GHG emissions in Canadian agriculture – especially options pertaining to ruminant agriculture.

This then begs an obvious question: How long before UNFCCC calculation protocol is altered to include this (or a comparable) computation of the short and long-term warming effect of methane? This author can offer no informed opinion but rather the observation that 1) given the complexity of UNFCCC/IPCC processes and 2) negative attitudes towards animal, especially ruminant-animal agriculture within various UN agencies (see this tweet as an example), changes along the line supported by the research at Oxford University may be very difficult to achieve.

I express deepest appreciation to Dr. Vernon Baron, Agriculture and Agri-Food Canada, Lacombe Alberta; Dr. Frank Mitloehner, University of California, Davis California; Dr. Raymond Desjardin, Agriculture and Agri-Food Canada, Ottawa; and Dr. John Lynch, University of Oxford, England for professional advice and input used in making the calculations described above. However, they bear no blame for inadvertent errors present in the resulting product.