Unintentional unfairness when applying new greenhouse gas emissions metrics at country level
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 asGWP)has been suggested to compare contributions of longand short-livedGHGs, providing a close link between cumulative CO2-equivalent emissions and total warming.However, comparison factors for non-CO2GHGs under theGWPmetric depend on past emissions, and hence raise questions of equity and fairness when applied at any but the global level. The use ofGWPwould putmost developing countries at a disadvantage compared to developed countries, becausewhen usingGWP countries with high historical emissions of short-livedGHGs are exempted from accounting for avoidable futurewarming that is caused by sustaining these emissions.We show that when various established equity or fairness criteria are applied toGWP (defined here as eGWP), perceived national non-CO2 emissions vary by more than an order ofmagnitude, particularly in countries with highmethane emissions likeNew Zealand.We show that national emission estimates that useGWP are very sensitive to arbitrary choicesmade by countries and therewith facilitate the creation of loopholes whenCO2-equivalent emissions based on theGWP concept are traded between countries that use different approaches. In light of such equity-dependent accounting differences, GHGmetrics likeGWP should only be used at the global level. A common, transparent and equity-neutral accountingmetric is vital for the Paris Agreement’s effectiveness and its environmental integrity.