Agriculture is the Main Driver of Climate Change and Deforestation
About 10,000 year ago, humans started shifting from hunting and gathering for their food to domesticating their crops and animals, in what is called the Agricultural Revolution. This allowed human populations to grow rapidly, and to be able to engage and develop sectors other than agriculture. Later came the mechanization of agriculture, with the Industrial Revolution, allowing that today only 1 billion people working in agriculture are able to feed the other 6.5 billion people in the world.
These, of course, were great and essential steps in the development of humanity, but they also marked the start of the ecological degradation and the environmental challenges that we are facing today.
It is hard to estimate how much a large and complex system like that of food contributes to climate change, but several studies allocate food systems with the largest share of greenhouse gas (GHG) emissions of all other human activities. The food system includes manufacturing of agricultural inputs (e.g. fertilizers, materials...), food production, processing and the supply chain. One study estimated that this entire system produces up to 1/3 of the global GHG emissions, with agricultural production (including crops, livestock, and the conversion of lands required for these activities) being the most polluting stage by far. However, this value may be very underestimated, as another study found that livestock production alone accounts for 51% of the GHG!
We may not have the universal value, but it is now widely accepted that agricultural production is if not the most, one of the most polluting economic sectors in the world.
These, of course, were great and essential steps in the development of humanity, but they also marked the start of the ecological degradation and the environmental challenges that we are facing today.
It is hard to estimate how much a large and complex system like that of food contributes to climate change, but several studies allocate food systems with the largest share of greenhouse gas (GHG) emissions of all other human activities. The food system includes manufacturing of agricultural inputs (e.g. fertilizers, materials...), food production, processing and the supply chain. One study estimated that this entire system produces up to 1/3 of the global GHG emissions, with agricultural production (including crops, livestock, and the conversion of lands required for these activities) being the most polluting stage by far. However, this value may be very underestimated, as another study found that livestock production alone accounts for 51% of the GHG!
We may not have the universal value, but it is now widely accepted that agricultural production is if not the most, one of the most polluting economic sectors in the world.
Figure 1 - Illustration of the sources of GHG emissions in agricultural production (©IPCC).
Agriculture is the main producer of other GHG than CO2: methane (CH4) and nitrous oxide (N2O). These molecules have a much more powerful global warming potential (GWP) per molecule CO2 (how much heat they capture from solar radiation): in their first 20 years in the atmosphere, CH4 has a GWP 56 times higher than CO2, and it is 280 times higher for N2O. CH4 mainly comes from the digestive process of ruminants (e.g. cattle, goats, sheep), called enteric fermentation, from their manure, rice production and biomass burning. N2O is emitted from the volatilization of excess amounts of synthetic fertilizers applied to soils, and from manure. Last, agricultural fields are also a source of CO2, from soil respiration (organisms living in the soil), biomass burning and the use of machinery (Figure 1). (FAO 2014)
The land-cover change that is needed to establish croplands and pastures for livestock (e.g. Figure 2), and their consequent degradation of lands, are other significant indirect sources of CO2. The conversion of lands produces about 12% of the world GHG emissions. Clearing lands also eliminates the C sequestration potential of the previous vegetation, and over 80% of agricultural lands have replaced the most important terrestrial C sinks: tropical forests.
The land-cover change that is needed to establish croplands and pastures for livestock (e.g. Figure 2), and their consequent degradation of lands, are other significant indirect sources of CO2. The conversion of lands produces about 12% of the world GHG emissions. Clearing lands also eliminates the C sequestration potential of the previous vegetation, and over 80% of agricultural lands have replaced the most important terrestrial C sinks: tropical forests.
Figure 2 - A Palm oil monoculture in Indonesia, a major source of GHG emissions and a species extinction hotspot (©Rhett Butler, Mongabay)
Deforestation is therefore the main way in which agriculture has expanded across the globe, currently claiming about 38% of the world’s terrestrial surface (croplands and livestock), greater than the size of Asia and Europe together. And this estimate is projected to further expand between 10 and 25% by 2050 with the increasing food demand from a growing and increasingly rich world population.
This extension has yielded agriculture the top rank among drivers of terrestrial biodiversity loss. By altering ecosystem functions, declines in biodiversity reduce agricultural productivity, and therefore threaten the capacity to feed a growing population.
Diego Garcia-Vega - October 14th 2017
This extension has yielded agriculture the top rank among drivers of terrestrial biodiversity loss. By altering ecosystem functions, declines in biodiversity reduce agricultural productivity, and therefore threaten the capacity to feed a growing population.
Diego Garcia-Vega - October 14th 2017