Global methane levels growing faster: study

Global concentrations of methane, a powerful greenhouse gas and cause of climate change, are now growing faster in the atmosphere than at any other time in the past two decades, a new study has found.
Researchers found that methane concentrations in the air began to surge around 2007 and grew precipitously in 2014 and 2015.
In that two-year period, concentrations shot up by 10 or more parts per billion annually.
It is a stark contrast from the early 2000s when methane concentrations crept up by just 0.5 parts per billion on average each year.
The reason for the spike is unclear but may come from emissions from agricultural sources and mainly around the tropics - potentially from farm sites like rice paddies and cattle pastures.

The findings may give new global attention to methane - which is much less prevalent in the atmosphere than carbon dioxide but is a more potent greenhouse gas, trapping 28 times more heat.

While research shows that the growth of carbon dioxide emissions has flattened out in recent years, methane emissions seem to be soaring.
"The leveling off we've seen in the last three years for carbon dioxide emissions is strikingly different from the recent rapid increase in methane," said Robert Jackson, professor at Stanford University.
"The results for methane are worrisome but provide an immediate opportunity for mitigation that complements efforts for carbon dioxide," Jackson said.

Methane is a difficult gas to track as it can come from many different sources. Those include natural sources like marshes and other wetlands.
However, the bulk - about 60 percent - of methane added to the atmosphere every year comes from human activities.
They include farming sources like cattle operations - cows expel large quantities of methane from their specialised digestive tracks - and rice paddies - the flooded soils make good homes for microbes that produce the gas.
A smaller portion of the human budget, about a third, comes from fossil fuel exploration, where methane can leak from oil and gas wells during drilling.

"Unlike carbon dioxide, where we have well described power plants, almost everything in the global methane budget is diffuse," Jackson said.
A range of information - such as from large-scale inventories of methane emissions, measurements of methane in the air and computer models - suggests that this cycle has shifted a lot in the last two decades.
"For the last two years especially, the growth rate has been faster than for the years before," said Marielle Saunois, assistant professor at Universite de Versailles Saint Quentin.
The study was published in the journal Environmental Research Letters.