Methane feedbacks to the global climate system in a warmer world

Methane (CH₄) is produced in many natural systems that are vulnerable to change under a warming climate, yet current CH₄ budgets, as well as future shifts in CH₄ emissions, have high uncertainties. Climate change has the potential to increase CH₄ emissions from critical systems such as wetlands, marine and freshwater systems, permafrost, and methane hydrates, through shifts in temperature, hydrology, vegetation, landscape disturbance, and sea level rise. Increased CH₄ emissions from these systems would in turn induce further climate change, resulting in a positive climate feedback. Here we synthesize biological, geochemical, and physically focused CH₄ climate feedback literature, bringing together the key findings of these disciplines. We discuss environment-specific feedback processes, including the microbial, physical, and geochemical interlinkages and the timescales on which they operate, and present the current state of knowledge of CH₄ climate feedbacks in the immediate and distant future. The important linkages between microbial activity and climate warming are discussed with the aim to better constrain the sensitivity of the CH₄ cycle to future climate predictions. We determine that 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 could become more important. Significant CH₄ emissions to the atmosphere from the dissociation of methane hydrates are not expected in the near future. Our key findings highlight the importance of quantifying whether CH₄ consumption can counterbalance CH₄ production under future climate scenarios.