On a cattle farm, most of the carbon usually comes from the herd, not the tractor: the methane cattle belch up as they digest grass outweighs the diesel. To see where your own farm’s carbon comes from, count it one activity at a time (herd, crop and planted forest), since nearly every source of emissions belongs to just one of them. Eduardo de Figueiredo and colleagues at São Paulo State University, in a 2017 paper in the Journal of Cleaner Production, found this digestive methane, which the IPCC calls enteric fermentation, at 87 percent of total emissions for beef cattle on degraded pasture, and it was the largest share in every system they compared.
This year a buyer, a cooperative or a bank may ask for the farm’s carbon number, and many farms have none. You can estimate it without measuring anything in the field, with the Tier 1 method of the Intergovernmental Panel on Climate Change (IPCC). Tier 1 is the simplest of the IPCC’s three levels: it multiplies what the farm already counts (head of cattle, kilograms of nitrogen, liters of diesel, hectares of forest) by published default factors. A growing forest works in the opposite direction and removes carbon, so it is subtracted from the total.
Take a mixed farm. It runs 400 beef cattle on 600 hectares of pasture and produces 120 tonnes of live weight a year. It grows grain on 400 hectares, spreading 5,000 kilograms of nitrogen and harvesting 1,200 tonnes. It has 5 hectares of eucalyptus. The cattle burn 6,000 liters of diesel a year, the crop 8,000 and the forest 300.
The total is expressed in carbon dioxide equivalent (CO₂e) because little of what a farm gives off is carbon dioxide itself: the herd emits methane and the fertilizer nitrous oxide, and each traps far more heat than CO₂. The calculation converts each gas into the amount of CO₂ that would trap the same heat, so the three activities add up to one number.
Livestock emits about 736 tonnes of CO₂e a year, the crop about 45 and the forest’s fuel less than one, while the 5 hectares of eucalyptus remove about 214. Net, the farm emits around 568 tonnes, and the small forest offsets a little over a quarter of what the rest emits.
How do you split the farm by activity?
Assign each source of emissions to the activity that caused it. The herd’s methane from digestion and from manure goes to livestock, the nitrous oxide from a crop’s fertilizer goes to that crop, and the carbon dioxide from fuel goes to whatever burned it. Two inputs are shared, and you split them yourself: diesel, because the same fuel runs the crop tractor and the cattle truck, and nitrogen, if you fertilize both pasture and crop.
The split matters for each product’s intensity, meaning its emissions per kilogram of beef or per tonne of grain. That figure should carry only what its own activity caused, and dividing the whole farm’s total by a single product would overstate it.
Why does the herd’s digestion outweigh the tractor?
Because a grazing animal belches tens of kilograms of methane a year, and methane traps twenty-five times as much heat as carbon dioxide over a century, the conversion factor in the IPCC’s Fourth Assessment Report. The IPCC’s default for a beef animal on Latin American pasture is 56 kilograms of methane a year, and its tables give every world region its own figure. That comes to 1.4 tonnes of CO₂e per head before anything else is counted. The nitrogen in the animal’s urine and dung adds about 375 kilograms of CO₂e more (worked out in the section on nitrogen), so each head carries about 1.8 tonnes.
Published studies point the same way. De Figueiredo’s team found digestive methane was still the largest share in the two systems that used fertilizer and other inputs, at 61 percent on managed pasture and 51 percent in an integrated crop, livestock and forest system. Modernel and colleagues, in a 2013 paper in Environmental Research Letters, compared grazing and feedlot beef in Uruguay and found digestion above 46 percent of emissions in every case, and 68 percent on native pasture. The diesel most people picture as the farm’s emission is the small share; the herd is the large one.
How much does the nitrogen add?
Close to 4.68 kilograms of CO₂e for each kilogram of nitrogen spread, charged to whichever activity got it. The IPCC’s default is that one percent of the nitrogen applied is given off as nitrous oxide; converted to the weight of the gas and multiplied by its warming factor of 298, that gives the 4.68. Count the nitrogen, not the fertilizer: a hundred kilograms of urea at 46 percent nitrogen is 46 kilograms of nitrogen.
On a grazing operation, though, the nitrogen that weighs most is not the nitrogen you buy. It is what the animals leave in urine and dung every day they spend on pasture. In the same IPCC chapter it counts as an emission from the soil, at a factor twice the fertilizer factor, two percent of the nitrogen deposited. A beef animal excretes about 40 kilograms of nitrogen a year, so the 400 head in the example leave 16,000 kilograms on the pasture. That comes to 150 tonnes of CO₂e, a fifth of the whole farm, from a figure almost no farm spreadsheet holds.
This estimate leaves out, on purpose, the nitrogen that escapes as ammonia gas or washes out with rainwater and turns into nitrous oxide somewhere else, because that share is far more uncertain. It also leaves out the carbon dioxide urea gives off as it breaks down in the soil. And pigs carry no urine and dung emission in this estimate, not because the IPCC factor excludes them (it sets the same two percent for pigs as for cattle), but because the region’s pigs are usually raised confined rather than on pasture, and no default weight for them is on hand to run the number.
How much does the diesel add?
About 2.68 kilograms of CO₂e per liter of diesel (roughly 10.1 per US gallon) and 2.27 per liter of gasoline, charged to the activity that burned them. Unlike the gases from the herd and the soil, this one is pure carbon dioxide, so no warming factor multiplies it. The per-liter figures come from the IPCC’s default factors for burning diesel and gasoline, converted through each fuel’s energy content and density. On a grazing operation fuel is a small share of the total, and splitting it between crop and cattle keeps each activity’s figure right.
How does a forest reduce the total?
A growing planted forest removes carbon, so it enters with a minus sign. In the IPCC’s forest chapter, the default growth for eucalyptus in the Americas is about 20 tonnes of dry matter per hectare a year. Counting the carbon in that growth and in the roots, and converting it to CO₂, gives about 43 tonnes of CO₂e removed per hectare a year, within a wide range of 13 to 85. That is nearly thirty-five times what a hectare of pasture emits in the example, which is why 5 hectares of eucalyptus offset a little over a quarter of the farm.
The same IPCC chapter carries three cautions. The figure is gross growth, and the harvest returns the carbon, so a standing forest is not permanent storage. It counts only the trunk and roots, not the soil. And the default is a broad average, so the result gives the forest’s order of magnitude, not a figure anyone can certify.
Which number should you track for each activity?
Its intensity: from the total you learn how large the farm’s emissions are, and with the intensity you can compare one year with the next. In the example, livestock comes to 1.23 tonnes of CO₂e per hectare of pasture and 6.14 kilograms per kilogram of live weight; the crop to 0.11 tonnes per hectare and 37.4 kilograms per tonne of grain. These figures fall when an activity produces more with the same emissions, even while the total holds or grows. The net balance, emissions minus removals, describes the whole farm and is usually what a buyer or bank asks for; with the intensity you see whether each enterprise is improving.
How far can a Tier 1 estimate go?
Tier 1 gets you the order of magnitude and which sources are largest, not a precise figure for your farm. Its default factors carry an uncertainty the IPCC puts at around thirty to fifty percent for livestock and far wider for forests. The estimate is not a measured inventory, and it will not stand in for one where a certificate is required.
A full life-cycle study also counts making the fertilizer, transport, fencing and sheds, and gets a higher figure: Modernel’s team put native-pasture beef in Uruguay at 16.7 kilograms of CO₂e per kilogram of live weight, against 6.14 in this example, which counts only what happens on the farm. Nor does the estimate judge the farm. With it you see where the emissions and the removal are, so the effort goes to the source that is actually large.
How does the example farm add up?
The example farm activity by activity, in metric tonnes of CO₂e.
| Activity | What goes in | CO₂e |
|---|---|---|
| Livestock | 400 beef cattle, 6,000 L diesel, 600 ha | emits 736 t |
| Crop | 5,000 kg N, 8,000 L diesel, 400 ha | emits 45 t |
| Forest | 5 ha eucalyptus, 300 L diesel | removes 214 t, emits under 1 t |
| Farm | emissions 781.6 t − removals 213.7 t | net 567.9 t (emitter) |
Rurivia calculation from the IPCC Tier 1 default factors applied to the example farm’s herd, nitrogen, diesel and eucalyptus area.
Where to start
Set aside an hour with the year’s fuel receipts, fertilizer invoices and herd records. The carbon footprint calculator on this site applies the same IPCC factors activity by activity and gives you a report to print; you enter what only the farm knows, the head count, the fuel split and the areas. The checklist covers what the calculator cannot know, and what you decide to do with the number.
The number goes out of date as soon as the herd, the crop or the planted area changes, so keep the year next to it. A block of eucalyptus cut this winter stops removing carbon and starts returning it, and a farm that kept last year’s report sees the balance move and knows why.
The same net number, with its year and its source, fills the environmental line of a first ESG report from what you already measure, the article on putting together a first sustainability report for a buyer or bank from records the farm already keeps. It also settles one line of the farm risk list, the article on ranking the farm’s risks by likelihood and impact, where a buyer’s carbon demand otherwise gets its impact score by guesswork. Other articles on the farm’s environmental records are in the sustainability section. Comparing this number each year with the last is the kind of routine check that farm management is built on.