Abstract
Much of the UK land sector’s environmental impact comes from the production of beef and dairy. Conventional metrics, which understate both the impact of methane reductions and the carbon opportunity cost of land, attribute most of this impact to enteric methane and land-use change from imported soy for feed. Recent developments in agricultural impact metrics necessitate investigation into whether continued reliance on conventional metrics could undermine national (and global) progress on climate and deforestation targets. This article estimates emissions and land use impacts associated with cattle in the UK and applies various combinations of metrics under four futures simulating a range of technological and policy levers. We find that the use of alternative metrics can highlight the potential impact of interventions that might have been overlooked when using conventional metrics, particularly encouraging more efficient production by including the carbon cost of foregone sequestration. We suggest that a range of metrics should be considered to ensure mitigation strategies which deliver on global outcomes, and show that estimates of absolute sectoral impact are acutely sensitive to methodological choices in how it is measured. We also find that the rank-ordering of different intervention strategies for the UK is largely insensitive to metric choice, though this may not be the case for all agricultural systems.
Generated Summary
This research investigates the utility of novel environmental impact metrics in UK ruminant mitigation, focusing on the environmental impacts of beef and dairy production. The study employs a combination of Global Warming Potential (GWP) metrics and land use metrics, specifically exploring how different metric choices influence the assessment of emissions and land use impacts associated with cattle in the UK. The research utilizes four future scenarios with varying technological and policy levers to simulate potential mitigation strategies and assess their effects on emissions profiles. The core methodology involves calculating emissions and land use impacts, applying different combinations of metrics, and analyzing the implications of these choices on mitigation incentives and outcomes. The objective is to assess how metric selection affects the development of national mitigation strategies for the livestock sector, potentially hindering or facilitating progress towards global environmental goals.
Key Findings & Statistics
- Globally, agriculture accounts for nearly a third of greenhouse gas (GHG) emissions [1] and uses about half of the world’s vegetated land [2].
- 75% of this agricultural land area is dedicated to rearing livestock, either as pastureland or to grow feed crops [3].
- According to UK national statistics, agricultural production accounts for just over 10% of national emissions [8] and uses 69% of the country’s land area [9].
- Globally, agriculture accounts for nearly a third of greenhouse gas (GHG) emissions [1].
- The global warming potential (GWP) metric is calculated as the relative radiative forcing caused by a pulse emission of a non-CO2 GHG relative to that due to a pulse of CO2 over a given time horizon [15, 16].
- GWP calculated over a 100 year time horizon (GWP100) is the most common metric at both the corporate and national levels [17, 18].
- While GWP (specifically over 100 years) has been widely used, it has also faced criticism.
- First published in 2016, GWP* (GWP- star) compares emissions of different GHGs in terms of CO2-warming-equivalent emissions, recognizing the difference in how cumulative and non-cumulative GHGs behave in the atmosphere [25-27].
- Globally, agriculture accounts for nearly a third of greenhouse gas (GHG) emissions [1] and uses about half of the world’s vegetated land [2].
- 75% of this agricultural land area is dedicated to rearing livestock, either as pastureland or to grow feed crops [3].
- According to UK national statistics, agricultural production accounts for just over 10% of national emissions [8] and uses 69% of the country’s land area [9].
- The IPCC defines land-use change (LUC) as ‘a change in land cover and an associated change in carbon stocks’ [44, 45].
- Direct LUC (dLUC) is calculated based on the emissions of conversion from one land cover to another, allocated over a ‘lookback period’, conventionally 20 years [46, 47].
- The carbon opportunity cost (COC) builds on these previous land occupation concepts, offering a metric that acknowledges the foregone sequestration created by human-appropriated land use [54, 55].
- In the scenarios which involve significant yield gains, we do not assume any land is taken out of production.
- The UK dedicates approximately 5.2 million hectares to grazing [81].
Other Important Findings
- The study finds that the use of alternative metrics can highlight the potential impact of interventions that might have been overlooked when using conventional metrics, particularly encouraging more efficient production by including the carbon cost of foregone sequestration.
- The research suggests that a range of metrics should be considered to ensure mitigation strategies deliver on global outcomes, and show that estimates of absolute sectoral impact are acutely sensitive to methodological choices in how it is measured.
- The study also finds that the rank-ordering of different intervention strategies for the UK is largely insensitive to metric choice, though this may not be the case for all agricultural systems.
- For more ambitious scenarios, the choice of GHG metric considerably changes the perceived magnitude of mitigation potential for a given intervention, whereas the influence of the land cost metric used is considerable regardless of mitigation ambition.
- The greatest percent reduction between scenarios comes from improved production efficiency (particularly when COC is included in the baseline).
- The difference between the INT and all existing technologies scenarios for any metric is marginal, suggesting that the choice of GHG metric becomes less important in scenarios of moderate mitigation ambition.
- The warming impact from COC alone accounts for between 30%-50% of the total contribution to warming by the end of the century.
Limitations Noted in the Document
- The analysis relies on several datasets, including the UK NIR and feed data from DEFRA. However, reliable information on the quantities and types of feed used specifically for cattle were particularly lacking, thus the impact of feed production has substantial uncertainty.
- The scenarios do not attempt to predict future conditions in a robust way, results are not prescriptive, but rather illustrative.
- The scenarios are stylized and do not attempt to predict future conditions.
- The study acknowledges mathematical symmetries between GWP* and dLUC, which can lead to leakage when reported at the sub-global level.
- The study acknowledges that the choice of reference year to begin calculations of warming may affect the stated absolute impact of a sector or activity.
- The study notes that there may be other contexts, such as where an intervention trades a decrease in nitrous oxide for an increase in methane, where metric choice does affect rank-ordering of mitigation decisions, so a case-by-case consideration of these effects is warranted.
Conclusion
The study emphasizes that the choice of GHG and land use metrics significantly influences the assessment of environmental impacts and the effectiveness of mitigation strategies in the UK cattle sector. The analysis reveals that the use of alternative metrics, especially those incorporating carbon opportunity costs (COC), can highlight the potential impacts of interventions that may be overlooked when using conventional metrics. The study also highlights that the rank-ordering of different intervention strategies for the UK is largely insensitive to metric choice, though this may not be the case for all agricultural systems. The choice of GHG metric considerably changes the perceived magnitude of mitigation potential for a given intervention, whereas the influence of the land cost metric used is considerable regardless of mitigation ambition. The research underscores the importance of considering a range of metrics to ensure mitigation strategies deliver on global outcomes. The choice of metric affects the absolute perceived impact of UK cattle, but does not affect the relative benefits of decisions going forward. This implies that while metric choice influences the perceived scale of harm, it doesn’t alter the relative effectiveness of different mitigation approaches. If the priority is minimizing global pressure to convert land, COC is the most helpful metric. If the objective is to minimize supply-chain emissions associated with deforestation, dLUC is potentially more informative. However, the study also points out that the impact of mitigation decisions on temperature depends on the choice of the metric used. The research suggests that meeting the goals of the Paris Agreement at a global scale requires all industries, agriculture included, to sustain no further warming for many decades. It also emphasizes the need to address the limitations of conventional metrics and the importance of considering a wider range of metrics to inform more effective and targeted mitigation strategies. The long-term effects of using GWP* are demonstrated. The research indicates that the choice of GHG metric becomes less important in the long-term, emphasizing the enduring impact of land use decisions. The study also highlights the need for a comprehensive approach that considers the benefits of reducing production and the potential for innovative interventions.