How necessary and feasible are reductions of methane emissions from livestock to support stringent temperature goals?

Agriculture is the largest single source of global anthropogenic methane (CH) emissions, with ruminants the dominant contributor. Livestock CH emissions are projected to grow another 30% by 2050 under current policies, yet few countries have set targets or are implementing policies to reduce emissions in absolute terms. The reason for this limited ambition may be linked not only to the underpinning role of livestock for nutrition and livelihoods in many countries but also diverging perspectives on the importance of mitigating these emissions, given the short atmospheric lifetime of CH.

How much do direct livestock emissions actually contribute to global warming?

Agriculture directly contributes about 10%-12% of current global anthropogenic greenhouse gas emissions, mostly from livestock. However, such percentage estimates are based on global warming potentials (GWPs), which do not measure the actual warming caused by emissions and ignore the fact that methane does not accumulate in the atmosphere in the same way as CO . Here, we employ a simple carbon cycle-climate model, historical estimates and future projections of livestock emissions to infer the fraction of actual warming that is attributable to direct livestock non-CO emissions now and in future, and to CO from pasture conversions, without relying on GWPs.

Probabilistic cost estimates for climate change mitigation.

For more than a decade, the target of keeping global warming below 2 °C has been a key focus of the international climate debate. In response, the scientific community has published a number of scenario studies that estimate the costs of achieving such a target. Producing these estimates remains a challenge, particularly because of relatively well known, but poorly quantified, uncertainties, and owing to limited integration of scientific knowledge across disciplines.

Broader perspectives for comparing different greenhouse gases.

Over the last 20 years, different greenhouse gases have been compared, in the context of climate change, primarily through the concept of global warming potentials (GWPs). This considers the climate forcing caused by pulse emissions and integrated over a fixed time horizon. Recent studies have shown that uncertainties in GWP values are significantly larger than previously thought and, while past literature in this area has raised alternative means of comparison, there is not yet any clear alternative.

Methane emissions from free-ranging cattle: comparison of tracer and integrated horizontal flux techniques.

Accurate measurements of methane (CH4) emission rates from livestock in their undisturbed natural environments are required to assess their impacts on radiative forcing (i.e., enhanced greenhouse effect) and the environment.