Recent changes in the growth rate of tropospheric methane

After carbon dioxide, methane is the second largest contributor to the enhanced radiative forcing of the atmosphere. The concentration of tropospheric methane has been increasing since the Industrial Revolution, though its rate of increase slowed in the 1980s and 1990s. It has been suggested that the slowing of the methane growth rate may reflect an approach to steady state. Here, we report recent changes in the methane growth rate that show that the concentration of methane is continuing to increase in the atmosphere, and that the decline of the methane growth rate during much of the 1980s and 1990s likely does not indicate an approach to steady state. Fluctuations in the methane growth rate may be driven in part by large-scale meteorological phenomena such as El Niño and La Niña events.