GHG Emissions and Agriculture

In a previous post we touched on the livestock sector's impact on greenhouse gas (GHG) emissions. Today, let's examine GHG emissions from the agricultural sector as a whole.

Emissions from agriculture occur in the form of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). CH4 and N2O are the most important sources of GHG emissions from agriculture, the agricultural sector contributing over 50% of the total amount anthropogenic emissions of these gases (Cole et al., 1997). Between 1990 and 2005, agricultural emissions of CH4 and N2O increased by 17%, equal to a an average annual emission rate of increase of approximately 60 megatonnes of CO2 equivalent (MtCO2-eq) per year (IPCC, 2007).

Agricultural fields in Brazil as seen from space (source: the Guardian)

Agricultural lands occupy approximately 40-50% of the Earth's land surface (IPCC, 2007), and can be clearly seen from space (e.g. above photo). Food systems today are so important that they contribute between 19 and 29% of the world's human-induced GHG emissions. Together, agriculture and forestry account for as much as one third of global GHG emissions (CGIAR, 2012). In 2008, approximately 9,800-16,900 MtCO2-eq were released from agricultural practices, agricultural production (including land cover change) comprising 80 to 86% of all food system emissions (Vermeulen, 2012).

Global agricultural emissions (CGIAR, 2013)

Various stages in the food production system are responsible for GHG emissions, as can be seen from the diagram above. The main three stages in the production of food include preproduction, production, and postproduction. By and large, the production stage which includes both direct and indirect emissions from agriculture contributes the largest portion of emissions. Within these stages of the food chain, regional variations exists with high-income countries contributing most to the postproduction stage (Vermeulen, 2012). 

Thornton (2012) argues that the effects of climate change will greatly affect the agricultural sector, and examines 22 common agricultural commodities' responses in the face of climate change. He states that "the world's agricultural system faces an uphill struggle", and that it will become a great challenge to feed global populations (as we saw with Foley, 2009). He also finds that the production of the most common commodity crops (wheat, maize, and rice) will be challenged by new weather patterns, as will the raising of livestock and catching of fish (two of the more common sources of protein). The Telegraph recently reported on the fact that the UK is now an importer of wheat because of large swings in weather conditions, exemplifying Thornton's (2012) findings (you can read the article here).

The UK was forced to switch from being an exporter of wheat to an
importer in 2013 (from the Telegraph)

At this point in our examination of current food systems, I'd like to take a little journey backwards in time. Remember when we talked about the origins of agriculture in November? We saw that the advent of agriculture about 10,000 years ago greatly altered human societies, and also the environment. What we didn't talk about was the early anthropogenic hypothesis, proposed by Ruddiman in 2003. Contrary to the popular notion that the Anthropocene began 150 to 200 years ago, altering the climate system by inputting CO2 and CH4 at industsrial rates, Ruddiman suggests that this transition in fact occurred thousands of years ago when agriculture was born. His three main arguments are that a) CO2 and CH4 concentrations anomalously began to increase 8,000 and 5,000 years ago, respectively; b) published explanations exist for mid- to late-Holocene gas increases which reject natural forcing; and c) wide arrays of archaeological, cultural, historical, and geologic evidence are available which point to anthropogenic impacts from early agriculture (in Eurasia in particular). Ruddiman's hypothesis is often criticised (see Ruddiman, 2007), but I thought it was worth mentioning and this post seemed like a good venue.

Regardless of when agriculture began to impact the climate system, it is clear that global food production is greatly contributing to climate change by inputting large amounts of GHGs into the atmosphere. The great challenge will be to produce enough food to feed the growing world, but at what cost? How will we manage to do so without imposing great climate change threats? If you're interested in mitigation strategies, you can read about it in chapter 8.4 of the IPCC's Fourth Assessment Report (AR4).

Thanks for reading, and have a Happy New Year!