The author estimates likely greenhouse contributions of methane emissions from solid waste landfills in the USA. These emissions appear significant: their effect, evaluated over the short term (< 10 years), is to add the order of 1 % to the total annual Increase of radiative forcing due to build-up of all green-house gases in Earth's atmosphere. Costs to mitigate landfill methane emissions were also estimated. Such costs appear quite low compared to those of most carbon dioxide mitigation approaches giving comparable benefit. This work, while preliminary, suggests landfill methane abatement is one of the more cost-effective measures that can be taken to address a component of the greenhouse problem.