How sensitive is the global peatland carbon pool to climate change?

Peatlands are important components of boreal and subarctic landscapes, and can be regionally important components of tropical landscapes. As boreal and subarctic peatlands store about one-third of the terrestrial soil carbon pool, peatlands play an important role as a long-term sink for carbon . In the last two decades, many studies have looked at the vulnerability of this carbon pool to the effects of global change (particularly warming and drying), and the potential feedbacks to the atmosphere a change in the peatland carbon pool might bring. The persistent imbalance between the production of decomposition of organic matter in waterlogged conditions results in the accumulation of peat. We synthesized studies looking at the effect of global change (especially warming and drying) on the carbon balance of peatlands. This synthesis shows that the magnitude of the warming or drying required to significantly affect the global peatland carbon pool is higher than the change that is expected over the 21st century, although this conclusion might be different when taking into account the effects of an increase in natural fire frequency or widespread permafrost thaw. We also show that direct anthropogenic impacts on peatlands, especially tropical peatlands, could result in the release of more peatland carbon in the 21st century than warming and/or drying. The simulation of peat accumulation responses to different drying scenarios using the Holocene Peatland Model also indicates that a very sharp and sustained decline in water table depth is required to significantly affect the carbon pool of a mature peatland, and that this response differs depending on how the vegetation is allowed to change in the course of the simulations