The authors write:
"This is either the longest and largest positive trend anomaly since >25 yr when systematic observations began or the onset of a new period of strongly increasing CH4 levels in the atmosphere."The cause isn't clear, but there are some indications it may be due to natural wetland emissions, perhaps due to precipitation from recent La Ninas.
A renewed increase would not be good news for the climate, since since methane is a strong greenhouse gas (23 times stronger than carbon dioxide, though it resides in the atmosphere for a much shorter time). Some scientists are worried that the warmer temperatures in the northern latitudes may lead to higher methane emissions from melting permafrost and marine hydrates, an example of the kind of positive feedback that amplifies anthropogenic CO2 warming.
Global data for methane levels comes out in a few months, I think.