Although agricultural greenhouse gases could make up as much as 30% of the world's manmade greenhouse emissions each year, there's been no global assessment since 2005. Now a team from the Food and Agriculture Organization of the United Nations (FAO) and the University of Aberdeen, UK, has created a database for 1961–2010 that considers emissions country by country and from all agriculture's emitting sectors, including key emissions from land use and land-use change.

"It's the first time that an international organization has created a coherent global database for greenhouse gases for agriculture, forestry and other land-use sectors, one that can be updated at yearly intervals," Francesco Tubiello of FAO told environmentalresearchweb. "This adds to the existing database on fossil-fuel emissions managed by the International Energy Agency. The FAO database can be used to support countries with low capacity identify their key emission sources and serve as a benchmark for international greenhouse-gas reporting."

The International Energy Agency updates fossil-fuel emissions each year, analysing the data by country. In 2007 the IPCC's fourth assessment report provided measures of agricultural greenhouse-gas emissions for 2004–2005. The new work extends this analysis further back in time and forward to 2010.

To calculate emissions, Tubiello and colleagues used data from FAOSTAT such as livestock numbers, amount of fertilizer applied and harvested area extent, along with default emission factors from the international reporting guidelines of the Intergovernmental Panel on Climate Change (IPCC).

"This approach allows for the creation of a global database with country detail," said Tubiello. "The platform facilitates data access and streamlining, identification of emission sources and data benchmarking, in line with new UNFCCC reporting requirements."

In the future, climate funding could be linked to more precise estimates of greenhouse emissions and mitigation potential, the team reckons. That would mean many developing countries would need a better assessment of their agricultural, forestry and land-use emissions.

"Our first results help quantify trends in the relative contribution of agriculture and deforestation to total anthropogenic forcing, showing that the ratio of agriculture emissions to total fossil-fuel emissions is declining," said Tubiello. "Results also indicate that emissions from agriculture are now comparable to those related to deforestation, and highlight the important role that degraded organic soils play in global emissions."

Growth in fossil-fuel emissions has outpaced the increase in emissions from agriculture, forestry and other land uses every decade from 1961 to 2010, the team found. Agricultural emissions increased by 1.1% a year from 2000 to 2010, to reach 4.6 Gt of carbon dioxide per year in 2010, or 5.8 Gt including emissions from biomass burning and organic soils. Over the same period, the ratio of agriculture to fossil-fuel emissions decreased from 17.2% to 13.7%, while the ratio of net deforestation to fossil-fuel emissions dropped from 19.1% to 10.1%. Indeed in 2010, emissions from agriculture were about 1.2 Gt of carbon dioxide per year larger than those from net deforestation.

"We are now expanding the database to include other relevant land-use emission components," said Tubiello. "We are providing this data to the current IPCC AR5 WGIII AFOLU (agriculture, forestry and other land uses) chapter. We will also make projections to 2030 and 2050, based on FAO projections of the underlying activity data such as projected livestock numbers and fertilizer use. Finally, we will begin to look at possible mitigation actions."

When it comes to capacity development, the team will use the new database in a series of regional workshops aimed at improving the ability of countries to identify their emissions from agriculture and report them to the international community. "We ran the first such workshop for the Asia-Pacific in October 2012 in Vietnam," said Tubiello. "Two additional workshops are planned this year in Latin America and Africa."

Tubiello and colleagues reported their work in Environmental Research Letters (ERL) as part of the Focus on Improving Quantification of Agricultural Greenhouse Gases.