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.
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