Lamb production is a key agricultural system within the UK and Wales in particular. While nationally significant, the sector contributes to climate change due to it being responsible for the release of various greenhouse gases (GHGs) namely enteric methane (CH₄), excretal nitrous oxide (N₂O), and carbon dioxide (CO2). It is therefore important to quantify emissions and consider how they could be reduced in the context of Net Zero climate change targets.
As lamb production generally occurs across a variety of altitudes, including lowland, upland and hill pasture grazing, the animals are subject to varying environmental conditions and dietary options. These factors have been linked to affecting enteric CH₄ and excretal N₂O emissions. However, there is a lack of assessment of emissions changes across the altitudes present in lamb production systems. Additionally, evaluation of how those changes affect carbon footprints (CFs) of lamb in comparison to default methodologies is limited.
This thesis aimed to fill this gap and assess altitudinal emissions changes within lamb production systems. Experimental work indicated that emissions differed across altitudes, with enteric CH₄ output and methane conversion factor (Ym) decreasing with increasing altitude. The same result was determined with excretal N₂O, with the N₂O-N emission factor (EF3prp) being lower in upland pasture than in lowland pasture. A CF tool was then developed that could disaggregate altitudinal variability in emission factors, forage characteristics and farm activity data. This determined that use of default methodologies vs. altitude specific resulted in a change in footprint results. When comparing a non-altitudinally disaggregated footprint with a disaggregated footprint, although both followed Intergovernmental Panel on Climate Change (IPCC) default emission factors (EFs), the CF increased. However, when site-specific EFs and forage characteristics were introduced, the footprint value decreased. This was attributed mostly to the site-specific forage characteristics as they were determined as having the most significant impact on the footprint.
Finally, an assessment of mitigation strategies was performed. It was determined that the GHG reduction effect of different strategies varied dependent on default vs. site-specific modelling, although improving productivity by increasing the number of lambs per ewe was consistently effective in terms of reducing emissions intensity. Increasing the number of animals grazing upland and hill sites was deemed to increase the footprint when following default methodologies, whereas the site-specific footprint saw a decrease. This highlights that default methodologies may not be full appropriate for assessing extensive grazing. It was also shown that some strategies decreased the CF while increasing the farm annual GHGs, highlighting that the desired outcome should be considered before implementing a strategy in the context of reaching Net Zero. This work also indicated that improvements to productivity on farm could result in reduced requirements for grazing land and therefore the opportunity for woodland creation. Improving the upland grazing to increase grass growth resulted in farm area being spared for woodland creation, resulting in 50% and 74% of annual farm GHGs being offset when following IPCC and site-specific footprints respectively.
Overall, this work highlighted that significant sources of uncertainty are still present within CF of lamb production. Disaggregation of EFs, forage characteristics and animal information produce different results to the use of default inputs. There is therefore progress required both in terms of emissions quantification at the different pastures to improve modelling inputs, but also to improve modelling techniques that better capture variability across systems. The work also highlights that it is possible to pair mitigation options across the different altitudes to spare land on farm and offset emissions via woodland creation. However, further work is required on the practicality of this at a farm level, and to improve robustness of the values used to estimate woodland carbon sequestration in a Welsh context.