Rates of atmospheric CH4 consumption of soils in temperate forest were compared in plots continuously enriched with CO2 at 200 µL L−1 above ambient and in control plots exposed to the ambient atmosphere of 360 µL CO2 L−1. The purpose was to determine if ecosystem atmospheric CO2 enrichment would alter soil microbial CH4 consumption at the forest floor and if the effect of CO2 would change with time or with environmental conditions. Reduced CH4 consumption was observed in CO2-enriched plots relative to control plots on 46 out of 48 sampling dates, such that CO2-enriched plots showed annual reductions in CH4 consumption of 16% in 1998 and 30% in 1999. No significant differences were observed in soil moisture, temperature, pH, inorganic-N or rates of N-mineralization between CO2-enriched and control plots, indicating that differences in CH4 consumption between treatments were likely the result of changes in the composition or size of the CH4-oxidizing microbial community. A repeated measures analysis of variance that included soil moisture, soil temperature (from 0 to 30 cm), and time as covariates indicated that the reduction of CH4 consumption under elevated CO2 was enhanced at higher soil temperatures. Additionally, the effect of elevated CO2 on CH4 consumption increased with time during the two-year study. Overall, these data suggest that rising atmospheric CO2 will reduce atmospheric CH4 consumption in temperate forests and that the effect will be greater in warmer climates. A 30% reduction in atmospheric CH4 consumption by temperate forest soils in response to rising atmospheric CO2 will result in a 10% reduction in the sink strength of temperate forest soils in the atmospheric CH4 budget and a positive feedback to the greenhouse effect.