The contribution of historical methane emissions to present-day warming

^{Adapted from Reisinger, 2024}

Between 1850–1900 and 2010–2019 global warming attributed to changes in greenhouse gas concentrations, excluding the cooling influences of aerosols and other factors, is estimated to be 1.5 °C. The Intergovernmental Panel on Climate Change has estimated that 0.5 °C of that global warming is attributable to global methane emissions.

In new research, The contribution of historical methane emission to present-day warming, commissioned by the Parliamentary Commissioner for the Environment, Dr Andy Reisinger has answered a fundamental next question: how much have individual sources of methane emissions – such as agriculture – contributed to present day warming globally?

Dr Reisinger found that of the 0.5 °C of warming from methane emissions, 60% was due to biogenic methane (from agriculture, waste and biomass burning) and 40% was due to fossil methane (from fugitive emissions and incomplete combustion of coal, oil and gas). Biogenic methane emissions from agriculture specifically contributed 0.19 °C of the 0.5 °C of present-day warming caused by methane emissions.

This means that methane emissions from agriculture have caused approximately 13% of present-day warming from changes in greenhouse gas concentrations. 

Importantly, the report also found that most of the warming from methane comes from the methane molecule itself – rather than the additional carbon dioxide that results from the decay of fossil methane. This source of carbon dioxide is estimated to contribute only about 2% to overall present-day warming from all methane emissions.

Understanding the international situation gives context to New Zealand’s position. Research has shown that livestock methane emissions account for 55% of New Zealand’s contribution to current warming from greenhouse gas emissions (excluding the effect of historical deforestation). Further research from the New Zealand Agricultural Greenhouse Gas Research Centre has found that methane will remain New Zealand’s largest single contributor to global warming for the next six decades, assuming greenhouse gas emissions continue at observed rates.