Browsing by Author "Pierrehumbert, Raymond"

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    Agriculture's contribution to climate change and role in mitigation is distinct from predominantly fossil CO2-emitting sectors
    (Frontiers, 2021-02-03) Lynch, John; Cain, Michelle; Frame, David; Pierrehumbert, Raymond
    Agriculture is a significant contributor to anthropogenic global warming, and reducing agricultural emissions—largely methane and nitrous oxide—could play a significant role in climate change mitigation. However, there are important differences between carbon dioxide (CO2), which is a stock pollutant, and methane (CH4), which is predominantly a flow pollutant. These dynamics mean that conventional reporting of aggregated CO2-equivalent emission rates is highly ambiguous and does not straightforwardly reflect historical or anticipated contributions to global temperature change. As a result, the roles and responsibilities of different sectors emitting different gases are similarly obscured by the common means of communicating emission reduction scenarios using CO2-equivalence. We argue for a shift in how we report agricultural greenhouse gas emissions and think about their mitigation to better reflect the distinct roles of different greenhouse gases. Policy-makers, stakeholders, and society at large should also be reminded that the role of agriculture in climate mitigation is a much broader topic than climate science alone can inform, including considerations of economic and technical feasibility, preferences for food supply and land-use, and notions of fairness and justice. A more nuanced perspective on the impacts of different emissions could aid these conversations
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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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    Indicate separate contributions of long-lived and short-lived greenhouse gases in emission targets
    (Springer Nature, 2022-01-28) Allen, Myles R.; Peters, Glen P.; Shine, Keith P.; Azar, Christian; Balcombe, Paul; Boucher, Olivier; Cain, Michelle; Ciais, Philippe; Collins, William; Forster, Piers M.; Frame, Dave J.; Friedlingstein, Pierre; Fyson, Claire; Gasser, Thomas; Hare, Bill; Jenkins, Stuart; Hamburg, Steven P.; Johansson, Daniel J. A.; Lynch, John; Macey, Adrian; Morfeldt, Johannes; Nauels, Alexander; Ocko, Ilissa; Oppenheimer, Michael; Pacala, Stephen W.; Pierrehumbert, Raymond; Rogelj, Joeri; Schaeffer, Michiel; Schleussner, Carl F.; Shindell, Drew; Skeie, Ragnhild B.; Smith, Stephen M.; Tanaka, Katsumasa