Retrospective and projected warming-equivalent emissions from global livestock and cattle calculated with an alternative climate metric denoted GWP*

Abstract

Limiting warming by the end of the century to 1.5°C compared to pre-Industrial times requires reaching and sustaining net zero global carbon dioxide (CO ₂) emissions and declining radiative forcing from non-CO ₂ greenhouse gas (GHG) sources such as methane (CH ₄). This implies eliminating CO ₂ emissions or balancing them with removals while mitigating CH ₄ emissions to reduce their radiative forcing over time. The global cattle sector (including Buffalo) mainly emits CH ₄ and N ₂O and will benefit from understanding the extent and speed of CH ₄ reductions necessary to align its mitigation ambitions with global temperature goals. This study explores the utility of an alternative usage of global warming potentials (GWP*) in combination with the Transient Climate Response to cumulative carbon Emissions (TCRE) to compare retrospective and projected climate impacts of global livestock emission pathways with other sectors (e.g. fossil fuel and land use change). To illustrate this, we estimated the amount and fraction of total warming attributable to direct CH ₄ livestock emissions from 1750 to 2019 using existing emissions datasets and projected their contributions to future warming under three historical and three future emission scenarios. These historical and projected estimates were transformed into cumulative CO ₂ equivalent (GWP ₁₀₀) and warming equivalent (GWP*) emissions that were multiplied by a TCRE coefficient to express induced warming as globally averaged surface temperature change. In general, temperature change estimates from this study are comparable to those obtained from other climate models. Sustained annual reductions in CH ₄ emissions of 0.32% by the global cattle sector would stabilize their future effect on global temperature while greater reductions would reverse historical past contributions to global warming by the sector in a similar fashion to increasing C sinks. The extent and speed with which CH ₄ mitigation interventions are introduced by the sector will determine the peak temperature achieved in the path to net-zero GHG.