Very Strong Atmospheric Methane Growth in the 4 Years 2014–2017: Implications for the Paris Agreement
▻https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2018GB006009
The rise in atmospheric #methane (CH4), which began in 2007, accelerated in the past 4 years. The growth has been worldwide, especially in the tropics and northern midlatitudes. With the rise has come a shift in the carbon isotope ratio of the methane. The causes of the rise are not fully understood, and may include increased emissions and perhaps a decline in the destruction of methane in the air. Methane’s increase since 2007 was not expected in future greenhouse gas scenarios compliant with the targets of the Paris Agreement, and if the increase continues at the same rates it may become very difficult to meet the Paris goals. There is now urgent need to reduce methane emissions, especially from the fossil fuel industry.
It is clear that if the Paris Agreement is to succeed, methane must be understood, but there are large unknowns. The key global deficiency, as noted by modeling studies (...) is the lack of long‐term measurement data from remote sites, especially in the tropics. There is urgent need for more in situ observations, from more locations, to constrain atmospheric inverse models of the methane budget. Isotopic measurement remains very sparse indeed. Satellite retrievals are unable to determine boundary layer methane abundance or to observe isotopologues accurately. To resolve the OH puzzle, more stations measuring long‐term time series of methane mole fraction, δ13CCH4 and δDCH4 are needed, especially in the tropics, as well as a tighter understanding of ongoing methyl chloroform (CH3CCl3) emissions. But funding agencies prioritize hypothesis‐testing and process‐study campaigns over long‐term monitoring.
If the main causes are increased anthropogenic emissions, they need to be reduced. If the increased methane burden is driven by increased emissions from natural sources, and if this is a #climate feedback—the warming feeding the warming—then there is urgency to reduce anthropogenic emissions, which we can control. If, however, the increase in the methane burden is driven by a decline in the oxidative capacity of the atmosphere, and this is a climate feedback, then the implications are serious indeed.