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

Abstract

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.

Updated Global Warming Potentials and Radiative Efficiencies of Halocarbons and Other Weak Atmospheric Absorbers

“…There continues to be a vigorous debate about the applicability of different emission metrics (e.g., Myhre et al, 2013); metric choice depends on the particular policy context in which they are applied, and the degree to which continuity of choice is important in that context (e.g., Allen et al, 2018; Cain et al, 2019; Rogelj & Schleussner, 2019). A specific development has been the suggested use of metrics that compare one‐off pulse emissions of long‐lived gases (such as CO 2 ) with step‐changes in emissions of short‐lived species (e.g., gases with lifetimes less than a few decades), on the basis that this leads to a more informed comparison of their ultimate impact on temperature; such approaches can either adopt GWP values, but adapt their usage (Allen et al, 2016) or more directly compute the pulse‐step equivalence (W. J. Collins et al, 2019).…”

Inconsistencies when applying novel metrics for emissions accounting to the Paris agreement

“…Taken together, we have shown that applying GWP * directly to the Paris Agreement would introduce major conflicts in the Agreement's architecture, undermine its overall internal consistency and deteriorate the environmental integrity of the targets that are set out in the Agreement's Articles 2 and 4. As a result of its dependency on historic emissions, applying GWP * to any other than the global level further raises fundamental questions of fairness and equity (Rogelj and Schleussner 2019). With the explicit reference to equity in Article 4 and given the national determined nature of the Paris Agreement, this further limits the scope of the applicability of the metric in climate policy.…”

Self-preservation strategy for approaching global warming targets in the post-Paris Agreement era

“…Noted that the grandfathering approach determines the national efforts relying on the current emissions and is not conducive to countries with relatively low emissions in the base year. Thus, it is often criticized in the literature 35,36 . However, we choose to include it in the average because it represents one of the five IPCC equity categories and is implicitly followed by many of the developed countries 8,37 .…”