Do Trees Remove Methane?
When it comes to methane (CH4) in the atmosphere, it is a topic that frequently sparks discussions about environmental issues. While the role of trees in removing methane is often debated, recent studies and observations provide valuable insights into this process.
Methane Removal in the Atmosphere
Most methane in the atmosphere does not remain there indefinitely. According to scientific research, about 600 megatons (MT) of methane enters the atmosphere annually, with a total atmospheric reservoir of approximately 4800 MT. This means the average residency time of methane is around 8 years, varying between 8.4 and 12 years depending on the source and additional atmospheric conditions.
Of this methane, 500 MT/year is consumed through oxidation in the lower atmosphere. The remaining methane is evenly distributed between degradation by UV radiation, ozone, and OH radicals in the upper atmosphere, and biological processes on the ground.
Methane Absorption by Plants
Plants play a significant role in absorbing methane, although their contribution is relatively small compared to atmospheric oxidation. Some plants are net "consumers" of methane, absorbing it both externally and internally. Methane absorption rates differ among plant types; for instance, bacteria can absorb up to 0.1 ppm CH4/m2/h, while plants absorb up to 0.025 ppm CH4/m2/h in situ, or even more in laboratory settings, which is temperature-dependent.
It is clear from the evidence that plants do absorb methane, contributing to the overall natural methane cycle. However, their contribution is not substantial in the grand scheme of methane removal from the atmosphere.
Fast Methane Oxidation and Its Environmental Impact
Methane is removed from the atmosphere through oxidation, a process that is remarkably fast. Trees themselves are not involved in this oxidation process. Methane is retained in the atmosphere for only a short period, typically about a 12.5-minute chemical half-life. This rapid oxidation makes methane non-persistent and not a significant air pollution issue.
An illustrative example can be seen in the aftermath of the largest methane leak in U.S. history at the Porter Ranch development in Los Angeles. A photo taken at the scene, showing methane concentrations, clearly demonstrates that within just under 2 hours and with a wind speed of about 10 mph, the methane had oxidized and was completely gone, turning into water and CO2. It is crucial to note that methane emissions from city sewers are also significant but go undetected due to the rapid oxidation process.
Conclusion
Methane's rapid oxidation process makes it a non-issue in terms of air pollution. Trees and plants do contribute to the absorption of methane, yet their role is minimal compared to atmospheric and biological processes. It is important to recognize and appreciate these roles without overstating their significance. Methane should not be mistakenly perceived as a pollution problem due to its inherent nature.