Methane in the atmosphere stopped rising in the mid 90s, but it started again in 2007 and it’s been picking up pace the last four years, according to new research.
Earth’s atmosphere had a methane concentration below 750 parts per billion, or ppb for 10,000 years. It began rising in the 19th century and continued to climb until the mid 90s. It is thought to be the cause of around a third of the warming the planet has experienced since the beginning of the Industrial Revolution. Human activities pump out nearly 60 percent of all emissions of this potent greenhouse gas, half of which come from the fossil fuel industry.
Scientists thought methane levels might have reached an equilibrium when they reached around 1,775 ppb. They hoped efforts to reduce emissions could reverse the historical trend of rising methane levels. However, methane levels began growing again in 2007 and that growth accelerated in 2014, pushing methane levels up beyond 1,850 ppb.
Researchers have found the methane in the atmosphere has a changing chemical signature, with the average weight of methane getting lighter. While that seems to implicate biological emission sources, as they tend to produce light methane. Estimates of emissions from coal mines and oil and gas wells suggest that the contribution from fossil fuels is rising and those sources release heavier molecules of methane, which conflicts with researchers findings in the atmosphere.
Experts have proposed a possible reason for the difference, the heaviest methane, like fires and agricultural burning have decreased dramatically over the last few decades. If this source of the dropping levels of heavy methane, it would make atmospheric methane lighter on the whole, masking an increase in emissions from fossil fuels.
If methane keeps increasing, researchers say it could seriously endanger efforts to keep the planet’s temperature in check. Further complicating the issue are recently revised estimates moving the global warming potential of methane upward by 14%.
Regardless of the source of the recent increase, experts say there are ways to reduce methane concentrations in the atmosphere. One immediate and clear priority proposed is to plug leaks from oil and gas wells.