Browsing by Author "Jenkins, Stuart"

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    Ensuring that offsets and other internationally transferred mitigation outcomes contribute effectively to limiting global warming
    (IOP, 2021-06-23) Allen, Myles R.; Tanaka, Katsumasa; Macey, Adrian; Cain, Michelle; Jenkins, Stuart; Lynch, John; Smith, Matthew
    Ensuring the environmental integrity of internationally transferred mitigation outcomes, whether through offset arrangements, a market mechanism or non-market approaches, is a priority for the implementation of Article 6 of the Paris Agreement. Any conventional transferred mitigation outcome, such as an offset agreement, that involves exchanging greenhouse gases with different lifetimes can increase global warming on some timescales. We show that a simple "do no harm" principle regarding the choice of metrics to use in such transactions can be used to guard against this, noting that it may also be applicable in other contexts such as voluntary and compliance carbon markets. We also show that both approximate and exact "warming equivalent" exchanges are possible, but present challenges of implementation in any conventional market. Warming-equivalent emissions may, however, be useful in formulating warming budgets in a two-basket approach to mitigation and in reporting contributions to warming in the context of the global stocktake.
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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
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    Methane and the Paris Agreement temperature goals
    (Royal Society of Chemistry, 2021-12-06) Cain, Michelle; Jenkins, Stuart; Allen, Myles R.; Lynch, John; Frame, David J.; Macey, Adrian H.; Peters, Glen P.
    Meeting the Paris Agreement temperature goal necessitates limiting methane (CH4)-induced warming, in addition to achieving net-zero or (net-negative) carbon dioxide (CO2) emissions. In our model, for the median 1.5°C scenario between 2020 and 2050, CH4 mitigation lowers temperatures by 0.1°C; CO2 increases it by 0.2°C. CO2 emissions continue increasing global mean temperature until net-zero emissions are reached, with potential for lowering temperatures with net-negative emissions. By contrast, reducing CH4 emissions starts to reverse CH4-induced warming within a few decades. These differences are hidden when framing climate mitigation using annual ‘CO2-equivalent’ emissions, including targets based on aggregated annual emission rates. We show how the different warming responses to CO2 and CH4 emissions can be accurately aggregated to estimate warming by using ‘warming-equivalent emissions', which provide a transparent and convenient method to inform policies and measures for mitigation, or demonstrate progress towards a temperature goal. The method presented (GWP*) uses well-established climate science concepts to relate GWP100 to temperature, as a simple proxy for a climate model. The use of warming-equivalent emissions for nationally determined contributions and long-term strategies would enhance the transparency of stocktakes of progress towards a long-term temperature goal, compared to the use of standard equivalence methods. This article is part of a discussion meeting issue ‘Rising methane: is warming feeding warming? (part 2)’.
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    Quantifying non-CO2 contributions to remaining carbon budgets
    (Nature Publishing Group, 2021-10-14) Jenkins, Stuart; Cain, Michelle; Friedlingstein, Pierre; Gillett, Nathan; Walsh, Tristram; Allen, Myles R.
    The IPCC Special Report on 1.5 °C concluded that anthropogenic global warming is determined by cumulative anthropogenic CO2 emissions and the non-CO2 radiative forcing level in the decades prior to peak warming. We quantify this using CO2-forcing-equivalent (CO2-fe) emissions. We produce an observationally constrained estimate of the Transient Climate Response to cumulative carbon Emissions (TCRE), giving a 90% confidence interval of 0.26–0.78 °C/TtCO2, implying a remaining total CO2-fe budget from 2020 to 1.5 °C of 350–1040 GtCO2-fe, where non-CO2 forcing changes take up 50 to 300 GtCO2-fe. Using a central non-CO2 forcing estimate, the remaining CO2 budgets are 640, 545, 455 GtCO2 for a 33, 50 or 66% chance of limiting warming to 1.5 °C. We discuss the impact of GMST revisions and the contribution of non-CO2 mitigation to remaining budgets, determining that reporting budgets in CO2-fe for alternative definitions of GMST, displaying CO2 and non-CO2 contributions using a two-dimensional presentation, offers the most transparent approach.