Livestock and climate change: what if the key actors in climate change are... cows, pigs, and chickens?
Robert Goodland and Jeff Anhang's 2009 Worldwatch analysis reviewed direct and indirect greenhouse-gas sources linked to livestock, arguing that conventional inventories omitted or misallocated several important categories and therefore understated the sector's climate impact.
What the study did and found
Robert Goodland and Jeff Anhang's 2009 article “Livestock and climate change: what if the key actors in climate change are... cows, pigs, and chickens?” reassessed direct and indirect greenhouse-gas emissions associated with livestock. The authors reviewed categories they considered underestimated, overlooked or assigned to other sectors, and presented a tabulated accounting of livestock-related emissions. Their calculation produced an estimate of at least 32.6 billion tonnes of CO2-equivalent per year, or 51% of global anthropogenic greenhouse-gas emissions. They also discussed mitigation options, incentives for the food industry, marketing strategies and investment opportunities. The article was an analytical reassessment rather than a new field measurement study, and its result depended strongly on the accounting boundaries and assumptions adopted.
Why it is cited
The paper is cited because its 51% estimate sharply challenged lower contemporary livestock-emissions estimates and stimulated debate about system boundaries in greenhouse-gas accounting. Later discussions often use it as an example of how totals can change when land use, methane metrics, supply-chain activities and other indirect effects are treated differently.
Current mainstream assessments do not support the 51% figure as the standard global estimate for livestock. FAO's 2023 assessment using the Global Livestock Environmental Assessment Model estimated livestock agrifood systems at about 6.2 Gt CO2-equivalent in 2015, around 12% of anthropogenic greenhouse-gas emissions. Differences reflect both updated data and different accounting methods. IPCC assessments nevertheless confirm that livestock remain a major source of agricultural methane, especially from enteric fermentation, and also contribute through manure, feed production and land-use change.
The topic today
Today, livestock climate assessment relies increasingly on life-cycle and supply-chain accounting that separates gases, production stages and mitigation options more explicitly. Priorities include reducing enteric methane, improving feed and animal health, better manure management, lowering emissions intensity and addressing land-use change. Demand-side measures and food-system choices are also considered in climate mitigation. The 2009 paper remains useful mainly as a historical challenge to accounting conventions, while current policy relies on more standardised inventory frameworks and updated global datasets.