In addition to the warming effect of current forcing and emissions, methane plays a role in climatic feedback mechanisms that can exacerbate warming and even lead to abrupt, catastrophic climate change in the future. This risk is primarily associated with the rapid release of carbon stores in the Arctic.
IPCC AR5 2014 WG2 SPM p. 15. ‘Examples that could lead to substantial impact on climate [i.e., amplifying carbon feedback] are the boreal-tundra Arctic system... carbon stored in the terrestrial biosphere (e.g., in peatlands, permafrost, and forests)'
IPCC AR4 2007 These [Arctic] changes will have cascading effects on key regional bio-physical systems and cause global climatic feedbacks