Developing countries constitute 70% of the potential for land-based mitigation from agriculture. Recognizing their potential, 52% of developing countries included decreasing greenhouse gas emissions from the agriculture sector in their plans to limit global warming prepared for the 2015 Paris climate change conference (COP21) and the Paris Agreement. But this research finds that the available methods to calculate emissions from agriculture can produce spurious estimates, a serious barrier to predict or monitor future emissions reductions.

Agriculture and climate scientists and climate policy leaders need tools to rapidly estimate emissions from agriculture and assess the potential impacts of policy and agricultural practice changes on emissions. This has catalyzed the development of “greenhouse gas calculators,” simple accounting tools that use a mix of emission factors and empirical models to calculate emissions with minimal input data. The calculators use methods and data from IPCC guidelines - the same methods used by national governments to report their greenhouse gas emissions. Governments are not the only stakeholders that have adopted greenhouse gas calculators. Companies, project managers, and farmers also use greenhouse gas calculators to anticipate or monitor the effects of agricultural practices.

Meryl Richards, lead author of the study and scientist for the CGIAR Research Program on Climate Change, Agriculture and Food Security (CCAFS) based at theGund Institute for Ecological Economics at the University of Vermont, explained:

Calculators are useful for getting a general sense of the relative contribution of different activities to greenhouse gas emissions. However, even the best available calculators will not be able to provide precise estimates for developing countries if the calculators are based on data sets from countries with very different agricultural systems.

Current tools have mixed results 

The study compared field measurements of soil emissions from smallholder farmers’ fields in Africa, Asia, and Latin America, with estimates produced by two of the most commonly used greenhouse gas calculators: the Cool Farm Tool, developed by the University of Aberdeen and the Sustainable Food Lab, and the Ex-ante Carbon Balance Tool (EX-ACT), developed and used by the Food and Agriculture Organization of the United Nations (FAO). 

The calculators overestimated net GHG emissions 70% of the time, and 41% of the time the tool-predicted emissions were more than twice those obtained through field measurements. The tools were most likely to overestimate nitrous oxide emissions, which are generated primarily from fertilizer application.

The researchers also examined whether the calculators could predict the relative change in greenhouse emissions associated with a change in management. In other words, if a rice farmer switched from continuously flooding her fields to using alternate wetting and drying, would the calculators correctly predict whether emissions would increase or decrease?