Global Methane, Project MOYA, and the UK’s Net Zero target
The amount of methane in the air is growing rapidly, and this growth is among the greatest challenges to the success of the UN Paris Agreement. After rising for over two centuries, very sharply in the 1980s, methane appeared to have equilibrated in the 1999-2006 period. But in 2007 growth resumed, accelerating in 2014 onwards. Over the 19th and 20th centuries, atmospheric methane had been becoming richer in 13C, indicating fossil fuel emissions were driving growth. But simultaneously with resumption of growth in 2007, the trend of the past two centuries has been reversed, with methane now growing richer in 12C.
Much of the growth in recent years has been in the tropics and warm temperate regions. In 2014, growth was global. Potential drivers of growth include warming tropical wetlands and more cattle, as well as a complex array of anthropogenic inputs including fires and fossil fuel emissions. It remains uncertain if the oxidative capacity of the atmosphere is declining. Weaker sinks would also shift the isotopic ratio to lighter values..
The UK’s NERC MOYA Global Methane Budget consortium (2016-2020) studies the changing methane burden, with time series measurement of methane and its isotopes at remote sites, field campaigns in the Arctic, Europe, and tropics, and through modelling studies. In particular, recent aircraft campaigns in tropical Africa and South America have measured large emissions from wetlands and fires.
The major anthropogenic sources are fossil fuel emissions, agriculture, fires and waste. Cutting emissions is feasible, especially from the gas and coal industries and also from tropical fires and waste sources. In many cases reduction measures may have low costs. In particular there is a need for tropical nations to participate, for example by covering landfills. If methane’s growth is not halted and reversed, the climate impact will severely challenge hopes of containing global warming.
_Nisbet et al. (2020) Methane mitigation: methods to reduce emissions, on the path to the Paris Agreement. Reviews of Geophysics in press Jan._
_Nisbet et al. (2019). Very strong atmospheric methane growth in the 4 years 2014–2017: Implications for the Paris Agreement. Global Biogeochemical Cycles, 33, 318-342._