The greenhouse gas effect of methane is much stronger than that of carbon dioxide, but comparatively short-lived. (c) pixabay

Due to the emission of highly climate-damaging greenhouse gases such as methane, animal husbandry - especially that of cattle - is considered to be the main cause of climate change within agriculture. A recent study by BOKU shows that the climate impact of the short-lived greenhouse gas methane in Austria is lower than usually assumed - per kilogram of beef, for example, the climate impact is about 40 percent lower.

The direct greenhouse gas effect of methane is much stronger than that of carbon dioxide and thus has a massive impact on the climate. At the same time, methane is comparatively short-lived. "If its emissions decrease, we can expect very positive effects in the short term and thus a lower rise in temperatures. We have now been able to show this for the first time for Austrian livestock using the new metric "GWP*" (GWP star), which is also prominently mentioned in the new IPCC Assessment Report of 2021," explains Stefan Hörtenhuber from the Institute of Farm Animal Science at BOKU Vienna.

Until now, the calculations did not take into account when greenhouse gas emissions per product unit continuously decrease because production becomes more efficient and what influence this has on the climate change-induced temperature increase. "In Austria, for example, dairy cow numbers have fallen by more than 40 percent since 1990, even though more milk is produced today than at that time," Hörtenhuber said. Thus, producing one liter of milk generates less methane today than in 1990 because there are fewer dairy cows in Austria producing methane overall.

Until now, the greenhouse gas potential was usually analyzed using the so-called GWP-100 value. This involves calculating the climate effect of additional emissions of methane, nitrous oxide or carbon dioxide over a period of 100 years. Methane is not fairly valued compared to carbon dioxide. The reason is that the climate effect of short-lived methane is fully felt in one century, but the effect of carbon dioxide, part of which remains in the atmosphere for thousands of years, cannot be fully represented in this way. The GWP* metric better accounts for this short-lived nature of methane. "The short-term climate change effect of rising methane emissions is significantly underestimated with GWP-100, and the effect is overestimated when emissions are falling," Hörtenhuber emphasizes.

Milk production only half as damaging to the climate

The use of the GWP* metric allows a dynamic perspective that includes both emissions and decomposition of short-lived methane. Thus, Austrian livestock production, which has been relatively stable in terms of animal numbers and emissions since 2005, performs significantly better when the GWP* metric is applied than with the conventional GWP 100 values. The study thus shows a lower climate effect of the current Austrian livestock industry than previously assumed: It decreases by almost 50% per kilogram of product for milk production, 40% for beef, and 5% for pork.

"Using the GWP* concept makes it clear that any conversion of greenhouse gases - such as from methane to carbon dioxide equivalents - is actually only an approximation of the actual climate impact," Hörtenhuber said. In addition, it must be taken into account that the concentration of methane in the atmosphere is still increasing worldwide - due to the extraction of crude oil, natural gas and coal, but also due to livestock farming. In addition, the climate impact of animal-based foods is higher than that of plant-based foods, "although the value of animal-based foods - for example in terms of protein, iron, zinc, folic acid or vitamin A or B12 content - is higher," adds the researcher. Other sustainability aspects, such as biodiversity and animal welfare, must be considered in addition to the climate impact. "For these reasons, but also because reducing methane has the potential to create more room for decarbonization in our entire economy in the short term, it is of great importance that we continue to pay attention to reducing our methane emissions," Hörtenhuber emphasizes.

The study is currently published in the trade journal Animal: 

You can hear more information on this topic in the podcast "Land schafft Leben" with BOKU scientist Werner Zollitsch: 

DI Dr. Stefan Hörtenhuber,
University of Natural Resources and Life Sciences Vienna
Institute for Farm Animal Science
Tel.: +43 1 47654 93229