Climate change: Agriculture is one of the most important anthropogenic activities contributing to climate change. Emissions from the entire food system—from production to consumption, and including agriculturally-driven land use change—are about a quarter of total greenhouse gas emissions. New technical, policy and institutional mitigation options will need to be developed and implemented to close the gap between current emissions projections and those needed to keep warming below 1.5-2 degrees. Examples of strategies for mitigating emissions include livestock breeds that produce less methane, greater retention of soil organic matter in soils, and more efficient use of nitrogen fertilisers.
Biosphere integrity: Agriculture has played a major role in shifting biosphere integrity, encompassing functional and genetic diversity, beyond the planetary boundary. Through land-use change (which leads to habitat fragmentation), genotype selection and intensification, agriculture has helped to drive loss in both genetic and functional diversity.
Land system change: This is rarely discussed without mentioning agriculture, which has been the most extensive driver of land use change on the planet. Between 2000 and 2010, agriculture is estimated to have driven 80 per cent of deforestation worldwide. To minimise further land-system change, food production must increase without driving further deforestation.
Freshwater use: Globally, about 84 per cent of extracted freshwater is used for agriculture; the figure is up to 90 per cent in very arid regions. With growing demand for crops for human and animal food, even more water will be required. Thus, as with the use of other natural resources, much greater efficiency in water use in food protection is key to not further exceeding this planetary boundary.
Biogeochemical flows: Agriculture has profoundly transformed the global cycles of nitrogen (N) and phosphorous (P) around the globe. Currently, agriculture’s share of total anthropogenic N and P use has been estimated at 86 and 90 per cent, respectively. Moreover, the use of fertilisers is expected to grow. The use efficiency of fertilisers can still be improved considerably. Only about 50 per cent of the nitrogen applied to soils is on average taken up by plants, with the rest leaching, eroding or volatilising away.
Ocean acidification: Caused by CO2 emissions to the atmosphere, ocean acidification is taking place at the fastest rate recorded in millions of years. The agriculture sector directly contributes to ocean acidification because it is a major source of CO2 emissions (e.g. as a driver of deforestation, from the manufacture and use of nitrogen fertiliser, and energy used for irrigation pumping).
Atmospheric aerosol loading: Agriculture contributes substantially to atmospheric aerosol loading. Emissions of the aerosol ‘black carbon’ may be the second most important contributor to global warming after CO2 emissions. Crop residue burning and dust from cultivated or desertified land due to wind erosion are both known to be significant global sources of atmospheric aerosols.
Stratospheric ozone depletion: While N2O is playing a comparatively minor role in ozone depletion, it is projected to grow in importance. N2O from soils is the main source of anthropogenic N2O and is primarily associated with the application of N fertilisers and manure to soils. 66-90 per cent of global anthropogenic N2O emissions can be attributed to agricultural activities.
Novel entities: The impact of anthropogenic chemicals on ecosystem functioning has been described for many case studies and agriculture is strongly implicated. Many pesticides, for example, are used widely in both agri- and aquaculture and are typically highly biologically active.