Scientists struggle to explain a worrying rise in atmospheric methane

EVERY year human endeavours emit 50bn tonnes of “carbon dioxide equivalent”. This way of measuring things reflects the climatic importance of CO₂, which traps heat in the atmosphere for centuries before it breaks down, compared with other, shorter-lived greenhouse gases.

Of that 50bn-tonne total, 70% is carbon dioxide itself. Half the remaining 15bn tonnes is methane. In the past decade methane levels have shot up (see chart), to the extent that the atmosphere contains two-and-a-half times as much of the gas as it did before the Industrial Revolution. Earlier this month America’s National Oceanic and Atmospheric Administration (NOAA) confirmed another sharp rise in 2017.