Overview
Greenhouse gas emissions refer to the anthropogenic production of certain gases which are known to trap heat in the atmosphere. Increased emissions result in higher concentrations of greenhouse gases present in the atmosphere, accelerating global warming. The global warming potential of GHGs is determined as a function of radiative forcing (the effect of each unit of gas on the level of energy remaining on the Earth), mean lifetime, and emissions (total quantity of gas emitted). Several GHGs (water vapor, carbon dioxide, ozone, methane, and nitrous oxide) occur naturally, but have increased in production due to human activity, while others do not occur naturally and were created entirely through anthropogenic means. The effects of these GHGs are compared by using the global warming potential (GWP) of each gas, and standardizing in terms of carbon dioxide equivalents. Essentially, this means that a certain amount of one GHG can be converted into the amount of carbon dioxide with the same GWP.
Agricultural GHG Emissions
Globally, the food system contributes 21 to 37% of all human GHG emissions, surpassing both industry and transport. Agriculture is a source of three main GHGs: carbon dioxide, methane, and nitrous oxide. Agricultural activities primarily contribute to carbon dioxide emissions through on-farm energy use, deforestation, burning, drainage of wetlands, and tillage. Methane is released primarily through enteric fermentation and manure management, while nitrous oxide is emitted through nitrogenous fertilizers and cropping practices. Soil and organic matter involved in agriculture can also serve as carbon sinks, slightly offsetting emissions.
Impacts of GHG Emissions
GHG emissions directly lead to global warming by trapping heat in the atmosphere. The effects of global warming include more frequent and severe weather, including storms, heat waves, floods, and droughts. Global warming results in both the melting of ice sheets and thermal expansion of water, both of which contribute to rising sea levels, which will threaten coastal populations. Higher temperatures also cause an increase in ground-level ozone, creating more smog and directly harming human health.
Global warming forces changes in the behavioral patterns of wildlife and is correlated to an increased rate of extinction. GHG emissions also contribute to ocean acidification, as the ocean absorbs excess carbon dioxide in the atmosphere. Acidification causes major losses in the populations of marine life and also accelerates the rate of extinction.