Browsing by Author "Rees, Robert M."

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    Are single global warming potential impact assessments adequate for carbon footprints of agri-food systems?
    (IOP Publishing, 2023-07-18) McAuliffe, Graham A.; Lynch, John; Cain, Michelle; Buckingham, Sarah; Rees, Robert M.; Collins, Adrian L.; Allen, Myles; Pierrehumbert, Raymond; Lee, Michael R. F.; Takahashi, Taro
    The vast majority of agri-food climate-based sustainability analyses use GWP100 as an impact assessment, usually in isolation; however, in recent years, discussions have criticised the 'across-the-board' application of GWP100 in Life Cycle Assessments (LCA), particularly of food systems which generate large amounts of methane (CH4) and considered whether reporting additional and/or alternative metrics may be more applicable to certain circumstances or research questions. This paper reports a sensitivity analysis using a pasture-based beef production system (a producer of high CH4 emissions) as an exemplar to compare various climate impact assessments: CO2-equivalents using GWP100 and GTP100, and 'CO2-warming-equivalents' using 'GWP Star', or GWP*. The inventory for this system was compiled using data from the UK Research and Innovation (UKRI) National Capability, the North Wyke Farm Platform, in Devon, SW England. LCAs can have an important bearing on: (i) policymakers' decisions; (ii) farmer management decisions; (iii) consumers' purchasing habits; and (iv) wider perceptions of whether certain activities can be considered 'sustainable' or not; it is, therefore, the responsibility of LCA practitioners and scientists to ensure that subjective decisions are tested as robustly as possible through appropriate sensitivity and uncertainty analyses. We demonstrate herein that the choice of climate impact assessment has dramatic effects on interpretation, with GWP100 and GTP100 producing substantially different results due to their different treatments of CH4 in the context of carbon dioxide (CO2) equivalents. Given its dynamic nature and previously proven strong correspondence with climate models, out of the three assessments covered, GWP* provides the most complete coverage of the temporal evolution of temperature change for different GHG emissions. We extend previous discussions on the limitations of static emission metrics and encourage LCA practitioners to consider due care and attention where additional information or dynamic approaches may prove superior, scientifically speaking, particularly in cases of decision support.
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    Characterising the biophysical, economic and social impacts of soil carbon sequestration as a greenhouse gas removal technology
    (Wiley, 2019-09-18) Sykes, Alasdair J.; Macleod, Michael; Eory, Vera; Rees, Robert M.; Payen, Florian; Myrgiotis, Vasilis; Williams, Mathew; Sohi, Saran; Hillier, Jon; Moran, Dominic; Manning, David A. C.; Goglio, Pietro; Seghetta, Michele; Williams, Adrian; Harris, Jim A.; Dondini, Marta; Walton, Jack; House, Joanna; Smith, Pete
    To limit warming to well below 2°C, most scenario projections rely on greenhouse gas removal technologies (GGRTs); one such GGRT uses soil carbon sequestration (SCS) in agricultural land. In addition to their role in mitigating climate change, SCS practices play a role in delivering agroecosystem resilience, climate change adaptability, and food security. Environmental heterogeneity and differences in agricultural practices challenge the practical implementation of SCS, and our analysis addresses the associated knowledge gap. Previous assessments have focused on global potentials, but there is a need among policy makers to operationalise SCS. Here, we assess a range of practices already proposed to deliver SCS, and distil these into a subset of specific measures. We provide a multi‐disciplinary summary of the barriers and potential incentives toward practical implementation of these measures. First, we identify specific practices with potential for both a positive impact on SCS at farm level, and an uptake rate compatible with global impact. These focus on: a. optimising crop primary productivity (e.g. nutrient optimisation, pH management, irrigation) b. reducing soil disturbance and managing soil physical properties (e.g. improved rotations, minimum till) c. minimising deliberate removal of C or lateral transport via erosion processes (e.g. support measures, bare fallow reduction) d. addition of C produced outside the system (e.g. organic manure amendments, biochar addition) e. provision of additional C inputs within the cropping system (e.g. agroforestry, cover cropping) We then consider economic and non‐cost barriers and incentives for land managers implementing these measures, along with the potential externalised impacts of implementation. This offers a framework and reference point for holistic assessment of the impacts of SCS. Finally, we summarise and discuss the ability of extant scientific approaches to quantify the technical potential and externalities of SCS measures, and the barriers and incentives to their implementation in global agricultural systems.