A herd of 400 beef cattle on pasture emits about 736 tonnes of carbon dioxide equivalent (CO₂e) a year, and all the diesel burned on the same farm adds 38. CO₂e is the amount of carbon dioxide that would trap the same heat as the gases the farm gives off. When a buyer, a cooperative or a bank asks for your farm’s carbon number, count it one activity at a time: herd, crop and planted forest. The count tells you where to look first. Cutting a tenth of the diesel saves 3.8 tonnes of CO₂e a year, while cutting a tenth of the herd’s digestive methane saves 56. Enter your head count, kilograms of nitrogen, liters of diesel and hectares in the carbon footprint calculator and read the largest source first.
The numbers come from an example farm built for this article and placed in North Dakota. None of it is North Dakota data: the herd, the crop and the areas are invented, and the factors are the IPCC’s. The farm runs 400 beef cattle on 600 hectares (about 1,480 acres) of pasture and produces 120 tonnes (about 265,000 pounds) of live weight a year. A tonne here is a metric tonne, 1,000 kilograms. It grows grain on 400 hectares (about 990 acres), spreading 5,000 kilograms of nitrogen (about 11,000 pounds) and harvesting 1,200 tonnes. It has 5 hectares of eucalyptus. The cattle burn 6,000 liters of diesel a year (about 1,585 US gallons), the crop 8,000 and the forest 300.
The estimate uses the Tier 1 method of the Intergovernmental Panel on Climate Change (IPCC), the simplest of its three levels. Tier 1 multiplies what the farm already counts (head of cattle, kilograms of nitrogen, liters of diesel, hectares of forest) by published default factors, so nothing is measured in the field. A growing forest removes carbon, so it is subtracted from the total.
Livestock emits about 736 tonnes of CO₂e a year, the crop about 45 and the forest’s fuel less than one. The 5 hectares of eucalyptus remove about 214. Net, the farm emits around 568 tonnes, and the forest offsets 27 percent 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. 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 comes to 0.11 tonnes per hectare and 37.4 kilograms per tonne of grain.
| 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 781.9 t, removals 213.7 t | net 568.2 t emitted |
Give each activity its own diesel and nitrogen figures before you open the calculator.
Why does a 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 calls this digestive methane enteric fermentation. The IPCC’s table lists a default for each world region. For a beef animal it is 56 kilograms of methane a year in Latin America, which the calculator uses, and 53 in North America, where North Dakota lies. With 56, the digestion comes to 1.4 tonnes of CO₂e per head before anything else is counted. The 3-kilogram difference is worth 30 tonnes across 400 head.
The nitrogen in the animal’s urine and dung adds about 375 kilograms of CO₂e (worked out in the next section). Adding manure methane and diesel, each head carries 1.84 tonnes. The example also counts the herd on pasture all twelve months. In North Dakota, months on hay or in a feedlot change the sum, so write those months down.
The 25 for methane, and the 298 for nitrous oxide from fertilizer nitrogen, are the Fourth Assessment Report factors used here and in the calculator. The GHG Protocol corporate standard says companies should use GWP values from the most recent Assessment Report, may choose another report, and shall report which one they used. The most recent is the sixth. Its Table 7.15 gives 27.0 for methane from non-fossil sources and 273 for nitrous oxide. With those factors the example farm emits 812.9 tonnes and nets 599.2, about 5.5 percent above the 568.2 of the Fourth report. Write the report next to the number.
Published studies point the same way. De Figueiredo’s team in Brazil found digestive methane was 87 percent of total emissions for beef cattle on degraded pasture. It was still 61 percent on managed pasture and 51 percent in an integrated crop, livestock and forest system. Modernel and colleagues compared beef finishing systems in Uruguay and found digestion above 46 percent of emissions in every case, and 68 percent on native pasture. In the example, diesel is 5 percent of the farm’s emissions.
How much do the nitrogen and the diesel add?
Close to 4.68 kilograms of CO₂e for each kilogram of nitrogen spread, charged to the activity that 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 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. The 5,000 kilograms on the example crop add 23 tonnes.
On a grazing operation, the nitrogen that weighs most is the one nobody spreads. It is what the animals leave in urine and dung every day they spend on pasture. The IPCC counts it, in its chapter on managed soils, as a soil emission at a factor of two percent of the nitrogen deposited, twice the fertilizer factor. The IPCC’s default excretion for a beef animal in Latin America is 0.36 kilogram of nitrogen per 1,000 kilograms of body weight a day. With the default weight of 305 kilograms, that is about 40 kilograms a year, so the 400 head leave 16,000 kilograms on the pasture. That comes to 150 tonnes of CO₂e, 19 percent of the farm’s emissions.
The estimate leaves out the nitrogen that escapes as ammonia or washes out with rain and turns into nitrous oxide elsewhere, 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 it counts no urine and dung emission for pigs. The IPCC sets the same two percent for pigs as for cattle, but the estimate has no default pig weight to run the number.
Diesel adds about 2.68 kilograms of CO₂e per liter (roughly 10.1 per US gallon), and gasoline 2.27 per liter (about 8.6 per gallon), charged to the activity that burned them. This gas is pure carbon dioxide, so no warming factor multiplies it. The IPCC publishes the default factors for burning diesel and gasoline per unit of energy, and the calculator converts them to liters. In the example, the diesel of all three activities comes to 38 tonnes. Splitting it between crop and cattle keeps each activity’s figure right.
Count the kilograms of nitrogen in each bag, not the kilograms of fertilizer.
How much carbon does a planted forest take back?
About 43 tonnes of CO₂e per hectare a year for eucalyptus, within a wide range of 13 to 85. 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, with a range of 6 to 40. The conversion multiplies the 20 by 1.24 to add the roots, by 0.47 for the carbon share of dry matter, and by 44/12 to turn carbon into CO₂. A hectare of pasture emits 1.23 tonnes in the example, so a hectare of eucalyptus removes nearly 35 times that, and 5 hectares offset 27 percent of the farm.
Eucalyptus is the calculator’s default and the example’s choice. A North Dakota farm with other trees needs the IPCC’s factor for its own species and climate, which the same table lists by forest type. A farm with no planted forest has no removal, and its net equals its emissions: 781.9 tonnes in the example.
The same chapter carries three cautions. The figure counts growth only, and the IPCC’s accounting subtracts the wood harvested, so a block that is cut stops removing carbon and returns it. At Tier 1 the soil carbon of a forest is assumed not to change with management, so the soil is not counted. And the default is a broad average, so the result gives the forest’s order of magnitude, not a figure anyone can certify.
Note the month a block is cut, because its removal ends that day.
What do you write down first, and how far can the number go?
Write down the fuel, the fertilizer labels and the months on pasture, because only the farm knows them. The IPCC says that factors estimated with Tier 1 are unlikely to be known more accurately than 30 percent and may be uncertain to 50 percent for livestock, and the forest range is wider. Tier 1 gives the order of magnitude and which sources are largest. It does not stand in for a measured inventory where a certificate is required.
A full life-cycle study draws a wider boundary. Modernel’s team counted herbicide, insecticide and fertilizer made off the farm, and the example counts none of those. Their systems ran from 16.7 kilograms of CO₂e per kilogram of live weight gained on native rangeland to 6.9 on seeded pasture and feedlot. An enterprise’s intensity therefore depends on its productivity as much as on its emissions, and the comparison from one year to the next is the one that holds.
Set aside an hour with the year’s fuel receipts, fertilizer invoices and herd records. The calculator 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. Use the checklist for what the calculator cannot know and for what you decide to do with the number.
The number goes out of date when the herd, the crop or the planted area changes, so keep the year next to it. Comparing this year’s number with last year’s is a routine check of farm management, and the library’s sustainability section covers the farm’s other environmental records.