A solution to the misrepresentations of CO2-equivalent emissions of short-lived climate pollutants under ambitious mitigation

Allen, Myles; Shine, Keith P.; Fuglestvedt, Jan S.; Millar, Richard; Cain, Michelle; Frame, David J.; Macey, Adrian

doi:10.1038/s41612-018-0026-8

Cited by 302 publications

(291 citation statements)

References 39 publications

(64 reference statements)

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“…In contrast to this 'flow' based approach, GWP * translates short-lived flow pollutants to a 'stock' of a certain SLCF-caused CO 2 -equivalent warming in the atmosphere. Following Allen et al (2018), the CO 2 -equivalent emissions of non-CO 2 short-lived GHGs using GWP * is defined as…”

Section: Methodsmentioning

confidence: 99%

Unintentional unfairness when applying new greenhouse gas emissions metrics at country level

Rogelj

Schleußner

2019

Environ. Res. Lett.

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The 2015 Paris Agreement sets out that rapid reductions in greenhouse gas (GHG) emissions are needed to keep global warming to safe levels. A new approach (known as GWP * ) has been suggested to compare contributions of long-and short-lived GHGs, providing a close link between cumulative CO 2 -equivalent emissions and total warming. However, comparison factors for non-CO 2 GHGs under the GWP * metric depend on past emissions, and hence raise questions of equity and fairness when applied at any but the global level. The use of GWP * would put most developing countries at a disadvantage compared to developed countries, because when using GWP * countries with high historical emissions of short-lived GHGs are exempted from accounting for avoidable future warming that is caused by sustaining these emissions. We show that when various established equity or fairness criteria are applied to GWP * (defined here as eGWP * ), perceived national non-CO 2 emissions vary by more than an order of magnitude, particularly in countries with high methane emissions like New Zealand. We show that national emission estimates that use GWP * are very sensitive to arbitrary choices made by countries and therewith facilitate the creation of loopholes when CO 2 -equivalent emissions based on the GWP * concept are traded between countries that use different approaches. In light of such equity-dependent accounting differences, GHG metrics like GWP * should only be used at the global level. A common, transparent and equity-neutral accounting metric is vital for the Paris Agreement's effectiveness and its environmental integrity.

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Section: Methodsmentioning

confidence: 99%

Unintentional unfairness when applying new greenhouse gas emissions metrics at country level

Rogelj

Schleußner

2019

Environ. Res. Lett.

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“…The relevance of GWP 100 to the Paris Agreement has been discussed in recent papers (M. R. Allen et al, ; Fuglestvedt et al, ; Tanaka & O'Neill, ). CO 2 ‐equivalent emissions of methane calculated using GWP 100 do not predict the resultant warming, because methane does not remain in the atmosphere as long as CO 2.…”

Section: Constraints On the Paris Agreement Target Given Methane's Gmentioning

confidence: 99%

“…For the Kyoto Protocol the UNFCCC used a value of 21 from the IPCC's second assessment report, published in 1996, and a GWP 100 of 25 for the Doha Amendment covering 2013-2020 (http://unfccc.int/resource/docs/2013/cop19/ eng/10a03.pdf). The relevance of GWP 100 to the Paris Agreement has been discussed in recent papers (M. R. Allen et al, 2018;Fuglestvedt et al, 2018;Tanaka & O'Neill, 2018). CO 2 -equivalent emissions of methane calculated using GWP 100 do not predict the resultant warming, because methane does not remain in the atmosphere as long as CO 2.…”

Section: Constraints On the Paris Agreement Target Given Methane's Gmentioning

confidence: 99%

“…Methane is the second most important anthropogenic greenhouse gas (M. R. Allen et al, ; Etminan et al, ; G. Myhre et al, ). In the 1990s, the atmospheric methane burden trended toward equilibrium, which it reached by the end of the twentieth century (Dlugokencky et al, ), with little or no growth in its atmospheric burden in the early years of this century.…”

Section: Introductionmentioning

confidence: 99%

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Very Strong Atmospheric Methane Growth in the 4 Years 2014–2017: Implications for the Paris Agreement

Nisbet

Manning

Dlugokencky

et al. 2019

Global Biogeochemical Cycles

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473

447

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Atmospheric methane grew very rapidly in 2014 (12.7 ± 0.5 ppb/year), 2015 (10.1 ± 0.7 ppb/year), 2016 (7.0 ± 0.7 ppb/year), and 2017 (7.7 ± 0.7 ppb/year), at rates not observed since the 1980s. The increase in the methane burden began in 2007, with the mean global mole fraction in remote surface background air rising from about 1,775 ppb in 2006 to 1,850 ppb in 2017. Simultaneously the 13C/12C isotopic ratio (expressed as δ13CCH4) has shifted, now trending negative for more than a decade. The causes of methane's recent mole fraction increase are therefore either a change in the relative proportions (and totals) of emissions from biogenic and thermogenic and pyrogenic sources, especially in the tropics and subtropics, or a decline in the atmospheric sink of methane, or both. Unfortunately, with limited measurement data sets, it is not currently possible to be more definitive. The climate warming impact of the observed methane increase over the past decade, if continued at >5 ppb/year in the coming decades, is sufficient to challenge the Paris Agreement, which requires sharp cuts in the atmospheric methane burden. However, anthropogenic methane emissions are relatively very large and thus offer attractive targets for rapid reduction, which are essential if the Paris Agreement aims are to be attained.

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“…to report equivalents derived using GWP * , CO 2 -e for equivalents from conventional application of GWP 100 , and 'CO 2 -equivalents' as a generic term to describe either means of deriving equivalents). GWP * was further refined in Allen et al [17], showing that specifying a time-period (Δt) of 20 years over which to assess the change in SLCP emission rates (ΔE SLCP ), and scaling the CO 2 -w.e. per year of this period (i.e.…”

Section: Introductionmentioning

confidence: 99%

Demonstrating GWP*: a means of reporting warming-equivalent emissions that captures the contrasting impacts of short- and long-lived climate pollutants

Lynch

Cain

Pierrehumbert

et al. 2020

Environ. Res. Lett.

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205

159

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The atmospheric lifetime and radiative impacts of different climate pollutants can both differ markedly, so metrics that equate emissions using a single scaling factor, such as the 100-year Global Warming Potential (GWP 100 ), can be misleading. An alternative approach is to report emissions as 'warming-equivalents' that result in similar warming impacts without requiring a like-for-like weighting per emission. GWP * , an alternative application of GWPs where the CO 2 -equivalence of short-lived climate pollutant emissions is predominantly determined by changes in their emission rate, provides a straightforward means of generating warming-equivalent emissions. In this letter we illustrate the contrasting climate impacts resulting from emissions of methane, a short-lived greenhouse gas, and CO 2 , and compare GWP 100 and GWP * CO 2 -equivalents for a number of simple emissions scenarios. We demonstrate that GWP * provides a useful indication of warming, while conventional application of GWP 100 falls short in many scenarios and particularly when methane emissions are stable or declining, with important implications for how we consider 'zero emission' or 'climate neutral' targets for sectors emitting different compositions of gases. We then illustrate how GWP * can provide an improved means of assessing alternative mitigation strategies. GWP * allows warming-equivalent emissions to be calculated directly from CO 2 -equivalent emissions reported using GWP 100 , consistent with the Paris Rulebook agreed by the UNFCCC, on condition that shortlived and cumulative climate pollutants are aggregated separately, which is essential for transparency. It provides a direct link between emissions and anticipated warming impacts, supporting stocktakes of progress towards a long-term temperature goal and compatible with cumulative emissions budgets.

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A solution to the misrepresentations of CO2-equivalent emissions of short-lived climate pollutants under ambitious mitigation

Cited by 302 publications

References 39 publications

Unintentional unfairness when applying new greenhouse gas emissions metrics at country level

Unintentional unfairness when applying new greenhouse gas emissions metrics at country level

Very Strong Atmospheric Methane Growth in the 4 Years 2014–2017: Implications for the Paris Agreement

Demonstrating GWP*: a means of reporting warming-equivalent emissions that captures the contrasting impacts of short- and long-lived climate pollutants

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