  Earth systems may fall into an undesirable system state if 1.5 degrees
celsius (C) of warming is exceeded. Carbon release from substantial permafrost
stocks vulnerable to near-term warming represents a positive climate feedback
that may increase the risk of 1.5 C warming or greater. Methane (CH4) is a
short-lived but powerful greenhouse gas with a global warming potential 28.5
times that of carbon dioxide (CO2) over a 100 year time span. Because
permafrost thaw in the coming centuries is partly determined by the warming in
the 21st century, rapid reductions in methane emissions early in the 21st
century could have far reaching effects. We use a reduced complexity carbon
cycle model and a permafrost feedback module to explore the possibility that
accelerating reductions in methane emissions could help avoid long-term warming
by limiting permafrost melt. We simulate 3 extended Representative
Concentration Pathway (RCP) emission scenarios (RCP 2.6, 4.5, and 6) through
the year 2300 and impose methane mitigation strategies where we reduce CH4
emissions by 1%, 5% or 10% annually until the long-term scenario emission level
is reached. We find that accelerated rates of methane mitigation do not
sufficiently alter the global temperature anomaly to prevent or delay a
permafrost feedback, nor do they result in meaningful long term reductions in
temperatures. We find that the long-term magnitude of methane mitigation (i.e.,
long-term emission level) and not the rate of reduction, corresponds to
long-term temperature change. Therefore, policy and mitigation efforts should
emphasize durable decreases in methane emissions over rapidity of
implementation.
