11 february 2019

Atmospheric Methane Increases Could ‘Negate or Reverse Progress’ on CO2 Cuts

E.G. Nisbet et al, The Energy Mix, February 11, 2019

Increases in atmospheric methane between 2014 and 2017 could put the targets in the Paris Agreement out of reach, and point to the “urgent need to reduce methane emissions, especially from the fossil fuel industry,” according to a new research article published last week by the American Geophysical Union.

Methane is considered the second-most important greenhouse gas, shorter-lived than carbon dioxide but up to 86 times more potent while it remains in the atmosphere. Its sources include fossil fuel production, livestock, and landfills, and methane releases from fracked natural gas have raised extensive concern in recent years.

“The rise in atmospheric methane (CH4), which began in 2007, accelerated in the past four years,” the authors state in their summary of the paper. “The growth has been worldwide, especially in the tropics and northern mid‐latitudes.” That observation also indicates a shift over the last dozen years, from a time when the Arctic was seeing the greatest growth.

Pointing to a shift in the carbon isotope ratio in the methane, the authors say the overall increase, from 1,775 in 2006 to 1,850 parts per billion (ppb) in 2017, could reflect a decline in the “oxidative capacity” of the atmosphere to cleanse itself of methane, as well as increases caused by warming, fire, or human activity.

Methane’s increase since 2007 “was so unexpected that it was not considered in pathway models preparatory to the Paris Agreement,” they write. “The climate warming impact of the observed methane increase over the past decade, if continued at more than 5 ppb per year in the coming decades, is sufficient to challenge” the Paris targets.

“The current growth has now lasted over a decade,” they add. “If growth continues at similar rates through subsequent decades, evidence presented here demonstrates that the extra climate warming impact of the methane can significantly negate or even reverse progress in climate mitigation from reducing CO2 emissions.”

But human-generated methane emissions “are relatively very large, and thus offer attractive targets for rapid reduction, which are essential if the Paris Agreement aims are to be attained.”

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