Carbon dioxide is climate change’s villainous star. But methane, an even more potent greenhouse gas, is CO2’s lesser-known evil twin. Researchers now find methane levels in the atmosphere are on an escalating upward trend. That’s a problem because emission scenarios that limit global warming to 2 degrees Celsius assume methane levels will drop over the next 30 years.
To make matters worse, scientists aren’t really sure what’s causing methane to go up rather than down. If we have any hope of slowing climate change it’s a question that needs answers, says Sara Mikaloff-Fletcher, an atmospheric scientist at the National Institute of Water and Atmospheric Research in Wellington, New Zealand, in new work in the journal Science.
“We urgently need to determine why atmospheric methane continues to rise and whether it is possible for humans to slow it,” she said.
Like carbon dioxide, atmospheric methane has been rising since preindustrial times. But in previous research, Mikaloff-Fletcher and an international team of scientists showed methane levels plateaued for seven years starting in 1999. The researchers credited decreasing emissions, likely from the fossil fuel industry, for the downturn.
But then in 2007, methane in the atmosphere picked back up. Much of the swell came from agriculture. And a study published earlier this year by another group showed a second steep increase in methane amounts starting in 2014. Methane levels skyrocketed at rates not seen since the 80s. The findings showed that the real growth of atmospheric methane was much faster than scientists or policymakers had anticipated when putting together emissions goals.
The work demonstrated “how critically important it is for the atmospheric greenhouse gas community to work closely with the climate policy community,” Mikaloff-Fletcher said.
Methane only sticks around in the atmosphere for about a decade before turning into CO2. But it absorbs much more heat, making it a far more potent greenhouse gas.
The Intergovernmental Panel on Climate Change (IPCC) emissions scenarios that limit warming to 2 degrees C assume atmospheric methane will plummet by 10 parts per billion between 2010 and 2050. But according to the National Ocean and Atmospheric Administration methane has risen by nearly that much each year since 2014.
“If atmospheric methane continues to rise at current rates, it means we need to reduce carbon dioxide and other greenhouse gases even more drastically than previously thought,” Mikaloff-Fletcher explained.
Mikaloff-Fletcher says that more greenhouse gas measurements and models are needed to pin down where methane emissions are coming from and what’s driving the rapid rise. And time is running out.“We have a relatively narrow window of time remaining to reduce atmospheric greenhouse gas levels if we wish to avoid more than two degrees warming,” she said.