 Solution

Methane is an infrared-active greenhouse gas with absorption in the terrestrial thermal spectrum. Its direct forcing is supplemented by chemically induced changes in tropospheric ozone and stratospheric water vapor. Its finite atmospheric lifetime makes sustained emissions and emission pulses different experiments: stopping emissions permits the methane burden to decline much faster than the long tail of a carbon-dioxide perturbation. Quantitative comparisons require a specified emission mass, time horizon and treatment of indirect effects, as formalized by global warming potential.