Measuring emissions

Greenhouse Gas (GHG) emissions from farms are measured in part to honour international commitments; for example, Canada needs to provide reliable annual estimates of emissions from all important sources, including farms. However, emissions are also measured for scientific reasons: if you cannot measure emissions precisely, how can you know which of various practices best reduces emissions?

Without good estimates of emissions, how can you understand the underlying principles of GHG formation and release?

Measuring emissions of GHGs from farms is not easy; emissions come from many places on the farm: soils, animals of all kinds and machinery. Sometimes the gases seep slowly into the air; other times they spew in sporadic gusts.

To capture these emissions, scientists have devised a host of methods:

  • small chambers placed on soils or large chambers housing cows
  • instrumented towers downwind of fields or instrumented aircraft flying over farming regions
  • methods that require patient analysis of carbon change in soils over tens of years
  • measurements of carbon dioxide (CO2) in air, several times a second
  • analysis of air in tubes buried in the soil, or from tubes hung high in the air on balloons

No method is perfect, but each has its role. By pooling results from all methods, scientists obtain reasonably good estimates of emissions and the factors that control them. This understanding is then usually captured in models-sets of mathematical equations that can predict GHG emissions for any set of conditions.

Such models are already widely used, but research continues to make them even more robust and reliable.

The principle measurement techniques
Description of this image follows.

Description – The principle measurement techniques

Figure displays five measurement methods on a graph with two axes: Y axis is 'Time scale of Measurement' and X axis is 'Spatial Scale of Measurement'. Five gas measurement methods are located on the axes: Chamber, Laser, Tower, Aircraft and Balloon. Gas capture chamber technique is shown as appropriate for durations of an hour or less over areas of a metre or less. Laser technology is shown as appropriate for time periods of one hour to several days and over areas of one to 100m. Towers are used to measure over time periods ranging from one hour to more than a year and distances of 100m to 1000m. Aircraft can used to measure areas of one to ten kilometres and for parts of a single day. Balloons can be used for areas similar to aircraft but periods of time up to several days.

A variety of measurement techniques are used to estimate GHG emissions from Canadian agriculture. Each measurement technique is appropriate over a specific time and area, represented by the size of the photograph in the figure. By combining measurement techniques that cover different time frames and areas, scientists can estimate GHG emissions from areas smaller than one square metre to several square kilometres and from time frames of a few minutes to several years.
Source and Photo Credits: R. Desjardins, E. Pattey, Agriculture and Agri-Food Canada, Ottawa, Ontario and P.-L. Lizotte. McGill University, Montreal, Quebec

The amount of emissions we produce

On- and off-farm sources of greenhouse gas emissions
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Description – On- and off-farm sources of GHG emissions

Figure shows sources of greenhouse gas emissions attributed to agriculture both on- and off-farm. On-farm emissions include methane emissions from manure, nitrous oxide emissions from manure, soil cultivation, crop residue decomposition and fossil fuel combustion, and carbon dioxide emissions from crop residue decomposition, and fossil fuel combustion. Off-farm emissions carbon dioxide emissions in the production of electricity, fertilizers, pesticides, machinery and building supplies, and nitrate and nitrous oxide losses from leachates.

In 2009, Canada produced 690 million tonnes of CO2 equivalents (Mt CO2e) from all sources, mostly as CO2 from energy use. Agriculture accounted for about eight per cent of these emissions (56 Mt CO2e), largely as CH4 (about two-thirds) and N2O (about one-third). This value does not include emissions from energy use; if these are counted, then agriculture accounts for roughly 10 per cent of Canada's emissions.

As mentioned, farm soils remove substantial CO2 from the air when soils gain carbon under improved practices (about 12 Mt CO2e were removed in 2009). In fact, Canadian croplands have been a net sink for CO2 starting in about 1990. However, until recently the removals on croplands were offset by carbon losses from forests and grasslands recently converted to cropland. It is only since about 2000 that agricultural lands have been a net sink for CO2 when land use change is taken into account.

The annual total GHG emissions from farms in Canada have increased from 1990 to 2009 (See Figure below). The main driver is the increase in the beef and swine populations, although they have stabilized in recent years.

Since 2005, emissions from the agriculture sector have stabilized. Declines in emissions from livestock production are being offset by increases in emissions from crop production.

In 2009, a continued reduction in emissions from livestock production and a reduction in emissions from crop production resulted in an apparent decrease in emissions. However, this reduction may be insignificant in relation to inter-annual variability or climate variability from year to year.

Carbon dioxide, methane and nitrous oxide emissions and removals from 1990 to 2009 for Canadian agriculture
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Description - Carbon dioxide, methane and nitrous oxide emissions and removals from 1990 to 2009 for Canadian agriculture

The chart shows emissions and removals (sources and sinks) in CO2 equivalents on the y axis and years on the x axis. Values below 0 are sinks (removals) and values above 0 are emissions. If the C sinks are taken into account as emissions offsets, net emissions in agriculture have declined relative to 1990.

Carbon dioxide, methane and nitrous oxide emissions and removals from 1990 to 2009 for Canadian agriculture
CO2 Mt N20 Mt CH4 Mt total Mt
1990 10.91 26.78 21.08 58.77
1991 10.59 26.17 21.38 58.14
1992 8.78 26.57 22.22 57.57
1993 7.74 27.68 22.46 57.87
1994 5.93 28.72 23.26 57.91
1995 4.50 29.27 24.42 58.19
1996 3.61 30.38 24.80 58.79
1997 2.66 30.21 24.78 57.65
1998 1.82 30.68 24.86 57.36
1999 0.82 31.08 24.60 56.51
2000 -0.33 31.17 25.20 56.05
2001 -1.06 29.57 25.93 54.45
2002 -1.76 28.87 26.24 53.36
2003 -2.79 30.98 26.31 54.50
2004 -3.60 31.88 27.06 55.33
2005 -4.49 31.38 27.64 54.53
2006 -5.01 31.32 26.89 53.20
2007 -5.62 32.21 26.15 52.74
2008 -6.43 33.78 25.40 52.74
2009 -7.08 32.36 24.25 49.54

These estimates may not be perfectly accurate; all carry some uncertainty, in particular those for nitrous oxide (N2O). But they provide a reliable view of general trends and their uncertainty may slowly shrink with further research and gradually improving methods.

What will happen to GHG emissions in coming years? With growing demand for food and other products, livestock numbers and nitrogen additions may rise further, perhaps increasing CH4 and N2O emissions, unless new ways can be found to suppress them. Soil carbon gains (CO2 removals from the air), which have offset past increases in methane (CH4) and N2O emissions, may continue for some years, but not indefinitely; eventually, soil carbon approaches a maximum, typically a few decades after introducing new practices.

Even with good practices, therefore, it is hard to foresee farm GHG emissions falling appreciably over time. More important than reducing total emissions, however, may be finding ways to reduce emissions per unit of product. In the last 15 years, for example, dairy farmers have reduced CH4 emissions per kilogram of milk by about 13 per cent, and similar trends are occurring with beef and pork.

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