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Food protein: three big challenges of today

Livestock: where do GHG emissions come from?

On March 8th, 2022 |
4 min reading time
Katja Klumpp
Katja Klumpp
Engineer in Agroecology at INRAE
Key takeaways
  • Agriculture is the second largest GHG emitting sector in France. It accounts for almost 23% of the national total.
  • Livestock farming is responsible for 68% of methane emissions, while soil cultivation accounts for 80% of nitrogen emissions.
  • However, emissions are calculated with varying degrees of accuracy depending on the method adopted.
  • For example, the IPCC proposes three levels of accuracy using multiplier “coefficients” for each category of emitting sources, type of GHG and data related to the activities concerned.
  • It is essential to adjust our production methods to reduce the impact of livestock and agricultural production on GHGs while guaranteeing benefits for producers.

We often hear that live­stock farm­ing is a major emit­ter of green­house gas­es (GHG). Which is true. In fact, agri­cul­ture is the sec­ond largest sec­tor in terms of GHG emis­sions in France (23% of the nation­al total1). Live­stock farm­ing is respon­si­ble for 68% of methane emis­sions, while soil cul­ti­va­tion is respon­si­ble for 80% of nitrous oxide emis­sions. Resilience regard­ing these emis­sions depends above all on greater auton­o­my of farms and low­er con­sump­tion of meat prod­ucts by the population.

How are the total emis­sions of the main green­house gas­es (GHG) emit­ted by live­stock (methane, nitrous oxide and car­bon diox­ide) and exchanges with­in grass­land ecosys­tems calculated?

Kat­ja Klumpp. In France, the body respon­si­ble for these inven­to­ries is the Cen­tre tech­nique de référence en matière de pol­lu­tion atmo­sphérique et de change­ment cli­ma­tique (Citepa), which uses cal­cu­la­tion meth­ods rec­om­mend­ed by the IPCC2. Thus, there are dif­fer­ent meth­ods with three lev­els of accu­ra­cy. We can use cer­tain mul­ti­pli­ers for each cat­e­go­ry of emit­ting sources, type of GHG and data relat­ed to the activ­i­ties concerned.

The first lev­el is exces­sive­ly sim­ple. For exam­ple, to find out the emis­sion of methane (CH4) from live­stock farm­ing, we mul­ti­ply the num­ber of cows in France by the asso­ci­at­ed mul­ti­pli­er. Or to find out the emis­sion of nitrous oxide (N2O) from live­stock farm­ing, we mul­ti­ply the quan­ti­ty of syn­thet­ic nitroge­nous inputs spread by the mul­ti­pli­er coef­fi­cient (emis­sion fac­tors; bovine 52 kg CH4/head/year) asso­ci­at­ed with this gas. The cal­cu­la­tion is sim­ple, but with the dif­fer­ent vari­a­tions present on the farms, the result will be sub­ject to large mar­gins of error.

In the sec­ond lev­el of com­plex­i­ty, more infor­ma­tion will be added: cow met­rics (intake, ener­gy require­ment, weight), cow cat­e­go­ry (dairy, calf, bull, etc.), loca­tion (con­ti­nent), etc. Final­ly, the third lev­el of com­plex­i­ty takes into account para­me­ters such as feed qual­i­ty, rumen func­tion in a mech­a­nis­tic mod­el, etc. We can there­fore see that to be accu­rate, we need to have a lot of source data from the farms at our dis­pos­al. In our work as researchers, we then have the pos­si­bil­i­ty of refin­ing and improv­ing the mea­sure­ments and cal­cu­la­tion meth­ods at local farms, which we then pass on to nation­al or inter­na­tion­al organ­i­sa­tions so that they can inte­grate them into their cal­cu­la­tion methods.

The albedo effect

The albe­do effect is par­tic­u­lar­ly in the spot­light at the moment. To explain it briefly, the albe­do is the pro­por­tion of solar radi­a­tion reflect­ed from a sur­face into the atmos­phere. Depend­ing on the “colour” (and tex­ture) of the sur­face in ques­tion, more or less radi­a­tion is reflect­ed. Basi­cal­ly, when light is reflect­ed, it is not con­vert­ed into heat and there­fore helps to reduce glob­al warm­ing. Max­imis­ing the albe­do effect there­fore means favour­ing sur­faces that reflect light rather than sur­faces that absorb it and con­vert it into heat. The prob­lem here too is that you have to find the right com­pro­mise local­ly. For exam­ple, a per­ma­nent grass­land with a more species-rich cov­er tends to be dark­er than a tem­po­rary grass­land with rye­grass-clover. Sim­i­lar­ly for soil colour, light soils strong­ly increase the albe­do and con­tribute to a low­er ter­res­tri­al tem­per­a­ture. Con­verse­ly, on dark soils, the intro­duc­tion of inter­me­di­ate crops increas­es the albe­do. Nev­er­the­less, we have seen that grass­land soils have a greater capac­i­ty store car­bon than crop soils. The impor­tant thing to remem­ber is that there is no sin­gle solu­tion for live­stock farm­ing in the face of glob­al warm­ing and that hav­ing sev­er­al solu­tions will always be ben­e­fi­cial to be more resilient.

There are a lot of vari­ables for net GHG emis­sions of a farm. Can you go over these dif­fer­ent parameters?

This is typ­i­cal­ly a case where we are in the third lev­el of com­plex­i­ty. We will take into account all the vari­ables as you men­tion. The so-called per­ma­nent grass­lands (area still under grass) which can be more than six years old as well as more than one hun­dred years old. This six-year dura­tion delim­its the bor­der with so-called tem­po­rary grass­lands (<5 years) which are gen­er­al­ly in rota­tion with crops. The plant com­po­si­tion of these grass­lands can be more or less rich, have dif­fer­ent modes of use (mowed, grazed or a mix­ture of the two), be fer­tilised with min­er­al or organ­ic fer­tilis­er, and so on. All these para­me­ters will affect the capac­i­ty of the grass­land to store (long-term process) and sequester car­bon (short-term process, it depends on the incom­ing car­bon flows) and there­fore on its over­all GHG emission.

As far as ani­mals are con­cerned, it is impor­tant to know the basis of their diet, whether arable land (con­cen­trate, oil­cake, wheat, maize, etc.) or grass­land has been used for part of their feed, and whether they are part of the fer­til­i­sa­tion of the soil, either through organ­ic or min­er­al fer­tilis­er, or the direct appli­ca­tion of manure or dung to the graz­ing area. These three cru­cial para­me­ters have an impact on GHG emis­sions. And we can go even fur­ther and add para­me­ters such as soil cov­er (type of veg­e­ta­tion), plough­ing, num­ber and time of graz­ing cows per hectare of grass­land, etc. We are still talk­ing about esti­mates because it is very dif­fi­cult get very pre­cise results. Nev­er­the­less, from a strict­ly the­o­ret­i­cal point of view, it would be pos­si­ble to com­pen­sate for the GHG emis­sions from live­stock farm­ing by using the car­bon stor­age of grass­lands and by replac­ing part of the min­er­al fer­tilis­er by the nitro­gen fix­a­tion by legumes.

How can cli­mate objec­tives be rec­on­ciled with oth­er issues such as the reduc­tion of fine par­ti­cle and ammo­nia emis­sions and the preser­va­tion of water and soil quality?

For a long time, research has focused sole­ly on GHGs. In France, agri­cul­ture accounts for 53% of par­tic­u­late emis­sions, com­pared to 29% for indus­try, 11% for ter­tiary res­i­den­tial and 5% for road trans­port (Citepa, 2014). Accord­ing to Citepa, “crops” are respon­si­ble for near­ly 80% of the par­tic­u­late emis­sions from agri­cul­ture, the rest being linked to live­stock farm­ing. The con­tri­bu­tion of live­stock farm­ing to fine par­ti­cles (size < 10μm – PM10) would be less than 10% of the nation­al emis­sion main­ly from live­stock build­ings. Then, it is ammo­nia emis­sions, which con­tribute to the for­ma­tion of fine par­ti­cles (PM2.5).

To rem­e­dy this, a set of inter­na­tion­al reg­u­la­tions has been put in place to reduce NH3 emis­sions. It became appar­ent some years ago that there was an urgent need to adopt so-called mul­ti-cri­te­ria approach­es. For exam­ple, the good prac­tice guide for improv­ing air qual­i­ty is based on a “win-win” strat­e­gy3. Here the aim is to pro­vide the keys to reduc­ing ammo­nia emis­sions while pro­vid­ing farms with oth­er ben­e­fits and avoid­ing any trans­fer of pollution.

Some objec­tives can­not be rec­on­ciled, how­ev­er. As is the case with poul­try farm­ing, which emits less GHG but more ammo­nia and fine par­ti­cles. We must there­fore find the best pos­si­ble com­pro­mise, which is far from easy. With this in mind, research is under­way to pro­mote the auton­o­my of farms (cir­cu­lar­i­ty) and allow a bal­ance in the man­age­ment of these dif­fer­ent para­me­ters, par­tic­u­lar­ly exter­nal inputs.

Interview by Julien Hernandez
1IPCC, 2019: Sum­ma­ry for Pol­i­cy­mak­ers. In: Cli­mate Change and Land: an IPCC spe­cial report on cli­mate change, deser­ti­fi­ca­tion, land degra­da­tion, sus­tain­able land man­age­ment, food secu­ri­ty, and green­house gas flux­es in ter­res­tri­al ecosys­tems [P.R. Shuk­la, J. Skea, E. Cal­vo Buen­dia, V. Mas­son-Del­motte, H.- O. Pört­ner, D. C. Roberts, P. Zhai, R. Slade, S. Con­nors, R. van Diemen, M. Fer­rat, E. Haugh­ey, S. Luz, S. Neo­gi, M. Pathak, J. Pet­zold, J. Por­tu­gal Pereira, P. Vyas, E. Hunt­ley, K. Kissick, M. Belka­ce­mi, J. Mal­ley, (eds.)]. In press

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