The temporal and spatial behavior of the isotopic ratio of atmospheric methane can be quite different from that of total methane. Changes in the isotopic ratio are the result of shifts between isotopically different methane sources, as well as changes in the total amount of methane into which methane from sources is being diluted. As a result, the timescale for isotopic changes is often considerably longer than for changes in total methane, and large-scale spatial gradients of the isotopic ratio adjust very slowly to a new source configuration, in sharp contrast to total methane.