Methane feedbacks to the global carbon cycle in a warming climate – combining microbial and geochemical perspectives

Atmospheric methane (CH₄) concentrations are increasing again following a brief plateau between 1999 and 2006. CH₄ is produced in many natural systems that are vulnerable to change under a warming climate, yet current CH₄ budgets are not well constrained, let alone potential future shifts in CH₄ emissions. Climate change has the potential to increase CH₄ emissions from critical systems such as wetlands, permafrost, marine and freshwater systems, and methane hydrates, through shifts in temperature and hydrology, vegetation and landscape disturbance, and sea level rise. Increased CH₄ emissions from these systems will in turn induce further climate change, forming a positive climate feedback.
Here we synthesize both biological and physically focused CH₄ climate feedback literature, bringing together the key findings of these disciplines, something that has previously been missing at the global scale. We discuss environment-specific feedback processes (e.g. wetlands vs. methane hydrates), including the microbial, physical and geochemical inter-linkages and the timescales they operate on, to present the current state of knowledge on CH₄ climate feedbacks in the immediate and distant future.
We will discuss the important linkages between microbial activity and climate with the aim to better constrain the sensitivity of the CH₄ cycle to the future climate change.
From our synthesis, we determine that while higher emissions from wetlands will form the majority of the CH₄ climate feedback up to 2100, beyond this timescale CH₄ emissions from marine and freshwater systems and permafrost environments will be more important, alongside the potential for large CH₄ emissions from destabilised methane hydrates. Our key findings highlight the current lack of understanding of whether CH₄ consumption can counter balance CH₄ production under future climate scenarios.