Is methane the 'climate culprit'? The dangers of using imprecise, long-term GWP for methane to address the climate emergency

TL;DR

This paper critiques the use of long-term GWP metrics for methane, highlighting their inadequacy in capturing short-term climate impacts, and proposes a dynamic alternative, GWPEFF(t), for better policy guidance.

Contribution

It introduces GWPEFF(t), a novel, dynamic metric that better represents methane's short-term warming effects compared to traditional static GWP100.

Findings

Recalculating emissions with GWP10 increases methane's impact to 90% of CO2.

GWP100 underestimates methane's immediate climate effects.

Proposes GWPEFF(t) for improved policy relevance.

Abstract

The United Nations Environmental Program's (UNEP) Emissions Gap Report, 2023, Temperatures hit new highs, yet world fails to cut emissions (again)'', and in 2024, No more hot air, emissions' massive gap between rhetoric and reality''. A climate emergency has been declared yet policies and emission reductions continue to fail. Global temperature anomalies in recent years have not been modelled well. Methane (CH4) is a potent greenhouse gas (GHG) with a short atmospheric half-life (~8.4 years), and a perturbation lifetime of 11.8 $\pm$ 1.8 yrs (IPCC AR6). It has a high, short-term impact on global warming: substantially greater than CO2. Traditional metrics such as the 100-year Global Warming Potential (GWP100) obscure the short-term, negative climatic effects of CH4, potentially leading to inadequate policy responses. This study examines the limitations of GWP100 in capturing the true, immediate climate impact of CH4 and its inability to incorporate varying emissions, explores alternative metrics, and discusses the multi-faceted implications of this under-reporting of CH4 emissions. Recalculation of 2024 Emissions Gap Report using a ten-year GWP of 105 increased CH4's warming effect to almost 90% of CO2, rather than 25% using a GWP100 of 28. We highlight the necessity of adopting a more immediate time horizon for CH4's warming effects, accelerating climate emergency action, while recognizing the adverse effects of the rapid growth rate of CH4 emissions on reduction efforts. To overcome the limitations of GWP100, a static constant, we propose GWPEFF(t) which dynamically represents warming across various time periods. It is a novel, physically realistic measure that is simple to understand, and effective for policies in reducing short-term emissions such as CH4.