Trees: Nature's Hidden Methane Fighters

Forests have traditionally been valued for their carbon-sequestering abilities. By converting CO₂ into organic matter stored in trunks, branches, and roots, trees act as long-term carbon sinks. However, methane, which has a much greater heat-trapping potential than CO₂ over a short period, has not been prominently associated with forests until now.

Methane is responsible for about one-third of the observed warming since preindustrial times. Its atmospheric concentration has risen rapidly in the past two decades, driven by human activities and natural sources. While methane’s atmospheric lifetime is significantly shorter than CO₂’s—about ten years compared to centuries—its warming potential is approximately 80 times greater over a 20-year period. This means that reducing atmospheric methane levels can lead to quicker climate benefits than reducing CO₂ alone.

Methane Sources and Sinks

Understanding methane’s journey in the atmosphere involves identifying its sources and sinks. Wetlands are well-known as the primary natural source of methane emissions. Other contributors include livestock, landfills, and fossil fuel extraction. On the other hand, methane sinks—processes that remove methane from the atmosphere—are relatively limited. Soil microbes play a significant role in methane oxidation, breaking it down before it escapes into the atmosphere. Now, with the discovery of tree bark’s ability to absorb methane, forests offer an additional and unexpected methane sink.

Discovering Tree Bark’s Role in Methane Absorption

The recent study, conducted by a team of ecologists and climate scientists, marks the first large-scale investigation into the role of tree bark in methane exchange. Previous research had primarily focused on wetlands and trees in flooded environments, where lower portions of tree trunks are known to emit methane. However, methane exchange in trees growing on well-drained soils—representing the majority of the world’s forests—had remained largely unexplored.

The researchers measured methane exchange on hundreds of trees in diverse forests, spanning regions from the Amazon and Panama to Sweden and the United Kingdom. Using a simple yet effective plastic chamber attached to tree trunks and connected to a laser-based methane analyzer, they found that trees in these environments absorb methane from the atmosphere. Notably, methane absorption became more pronounced higher up the trunk, suggesting that this process dominates overall methane exchange.

Quantifying the Global Impact

To estimate the global impact of this discovery, the team needed to calculate the total surface area of tree bark worldwide. Using advanced terrestrial laser scanning techniques, they mapped woody surfaces, from thick trunks to the finest twigs. Astonishingly, they found that if all the bark from the world’s trees were laid flat, it would cover the entirety of Earth’s land surface. This vast area represents an enormous potential for gas exchange between tree bark and the atmosphere.