There is a lot of interest on the role of pasture to sequester carbon in soil, to reduce atmospheric CO2 levels, to help mitigate global warming. However, the most widespread use of pasture in farming is grazing herbivores, the majority of which are cattle. Cattle are ruminants and produce the majority of the worlds methane production. Methane is a key greenhouse gas, so, farming ruminants on pasture is a double edged sword: soil under pasture has higher levels of organic matter / soil carbon, than under tillage thus reducing greenhouse gasses (GHGs), but, the livestock on top of the pasture are producing GHGs thereby increasing climate change. The net effect of this on climate change has been a hot topic of discussion for some time, with some people claiming that on balance grazing livestock on pasture creates a net reduction in GHGs and mitigates climate change while others say the effect is increased GHGs and negative impact on the climate.
The Food Climate Research Network (FCRN) recently put out a substantial report on this issue called “Grazed and Confused” based on the best avalible science, which makes a whole-of-system analysis of the climate impact of ruminants on pasture. This multidisciplinary study, by a large number of academics, from a global group of top-rate institutions, is pretty definitive. The report is important reading, but, is pretty technical in places, so FCRN have produced an easy to understand video of the key points, so if you find the report hard going, the video is essential viewing.
The conclusion is a wakeup for livestock farmers: Yes, soil carbon is higher under pasture compared with tillage, but, it reaches an upper limit and then plateaus, typically around 20 years, even with approaches, such as organic / biological / regenerative farming, that aim to maximise soil organic matter. This means that after soil carbon plateaus no more atmospheric CO2 is locked away. Land that has already been under pasture for that period of time also wont fix any more. However, ruminant livestock grazing the pasture produce methane continually and indefinitely. This means that under the majority of realistic scenarios, ruminant livestock grazing on pasture are net contributors to climate change.
It is important to note that the study boundaries were soil carbon sequestration and methane production, not the wider issues of soil quality, social issues, biodiversity, water use etc., so this study really needs to be part of a much larger analysis of the total environmental, social and economic impacts, but, within the bounds of its remit is it clear that ruminant livestock grazing pasture are a net contributor to global warming.
The Food Climate Research Network (FCRN) is an academic / science based network that “conducts, synthesises, and communicates research at the intersection of food, climate, and broader sustainability issues.” I consider it to be a particularly valuable, rigorous, and impartial source of information on the intersection of agriculture, climate change and sustainability. It is well worth signing up for their newsletter.