Mitigation and implications of methane emissions from dairy cow barns

Reaching the Paris Agreement temperature goals of no higher than +1.5°C or +2.0°C of global mean temperature change is quickly becoming difficult to reach by the end of the century. Not making the Paris Agreement temperature targets will impact all aspects of human society.

 

Around 1/3^rd of global mean surface temperature changes, is estimated to be caused by methane making it the second most powerful greenhouse gas released anthropogenically.  Anthropogenic sources emit 349 Tg of methane per year and are responsible for more than 50% of global methane emissions. The main emitters are the energy sector (>36% of emissions) and agriculture (40%). Fortunately, methane is a short-lived greenhouse gas, and removal of anthropogenic emissions sources may dramatically change the global concentrations on decadal timescales.

 

In response to the unlikelihood that methane emissions will be attenuated sufficiently in the coming decade by production reductions, methane emission mitigation technologies are under development. However, these technologies are yet to be rolled out on an industrial scale. New methane mitigation technologies can reduce a 50 ppm emissions source at ~60% efficiency and require an air volume rate of 4.36e13 m3/yr to remove 1 Tg CH4 per year. The volume of air required to process low concentrations to make a substantive impact on total emissions is major roadblock to their implementation. For example, for CO2 capture—a related carbon mitigation method—many test technologies are constructing large independent ventilation facilities. However, novel methane emission mitigation technologies are currently being tested and evaluated in several countries. These new technologies may capture CH4 and/or convert CH4 to molecules with less radiative forcing potential.

 

Here, we propose using dairy cow barns as a viable pathway for methane emission mitigation by utilizing existing infrastructure while targeting a major source of agricultural methane. Currently, there are ~264 M dairy cows worldwide. In Europe, there are 23 M dairy cows, and ~33% are housed in barns annually. For example, 70% of Denmark’s and 90% of Italy’s dairy cows are housed annually. For the health and welfare of the animals, barns are ventilated to maintain comfortable temperature and humidities, as well as ventilate abhorrent gases, such as methane. Standards for ventilation require 400 m3/hr/cow (high heat situations require 2500 m3/hr/cow), which is 3.5e6 m3/cow annually. A dairy cow emits between 55-100 kg CH4 per year. Which translates to 0.4-0.9 Tg CH4 per year for the ~7.59 M housed dairy cows in the European Union. The amount of air estimated to move through the EU dairy barns is 2.66e13 m3/yr and is within the estimated amount of air required to remove 1 Tg of CH4 from emerging technologies (4.36e13 m3/yr).  Implementation of this type of methane mitigation is feasible and with additional air recycling, potentially capture methane emissions from dairy cow barns.