In the past two decades, the rate of increase in the concentration of methane in the atmosphere has averaged about 1% per year, more than twice the rate of increase in the concentration of carbon dioxide.
(the rate of increase in the concentration of methane in the atmosphere; has averaged; about 1% per year; T:In the past two decades)
the rate of increase in the concentration of methane in the atmosphere
has averaged
about 1% per year T:In the past two decades