Long-term decline of global atmospheric ethane concentrations and implications for methane

TLDR: It is shown that global ethane emission rates decreased from 14.3 to 11.3 teragrams per year, or by 21 per cent, from 1984 to 2010, and suggested that reduced fugitive fossil fuel emissions account for at least 10–21 teragramS per year of the decrease in methane's global emissions, significantly contributing to methane’s slowing atmospheric growth rate since the mid-1980s.

Abstract: The longest continuous record of global atmospheric ethane levels is presented, showing that global ethane emission rates decreased by 21 per cent from 1984 to 2010, probably owing to decreased venting and flaring of natural gas in oil fields; decreased venting and flaring also account for at least 30 to 70 per cent of the decrease in methane emissions over the same period. Ethane is the most abundant non-methane hydrocarbon in the remote atmosphere and is a precursor to tropospheric ozone. This paper presents the longest continuous record of global atmospheric ethane levels assembled so far and finds that global ethane-emission rates decreased by 21% between 1984 and 2010. This can probably be attributed to a decrease in fugitive emissions, such as the venting and flaring of natural gas from oil fields, rather than a decline in its other major sources, biofuel use and biomass burning. Because methane shares ethane's main sources of emissions, this new long-term ethane record can be used to investigate changes in global methane levels. This leads the authors to suggest that reduced fugitive fossil-fuel emissions also account for 30–70% of the decrease in global methane emissions. After methane, ethane is the most abundant hydrocarbon in the remote atmosphere. It is a precursor to tropospheric ozone and it influences the atmosphere’s oxidative capacity through its reaction with the hydroxyl radical, ethane’s primary atmospheric sink1,2,3. Here we present the longest continuous record of global atmospheric ethane levels. We show that global ethane emission rates decreased from 14.3 to 11.3 teragrams per year, or by 21 per cent, from 1984 to 2010. We attribute this to decreasing fugitive emissions from ethane’s fossil fuel source—most probably decreased venting and flaring of natural gas in oil fields—rather than a decline in its other major sources, biofuel use and biomass burning. Ethane’s major emission sources are shared with methane, and recent studies have disagreed on whether reduced fossil fuel or microbial emissions have caused methane’s atmospheric growth rate to slow4,5. Our findings suggest that reduced fugitive fossil fuel emissions account for at least 10–21 teragrams per year (30–70 per cent) of the decrease in methane’s global emissions, significantly contributing to methane’s slowing atmospheric growth rate since the mid-1980s.