INCREASING atmospheric concentrations of the three main greenhouse gases—carbon dioxide, methane, and nitrous oxide— account for about 70% of anticipated global warming1, but the production–consumption budgets are not balanced for any of these gases2. Snow can cover between 44 and 53% of the land area of the Northern Hemisphere3 and may be several metres deep in alpine and sub-alpine regions for more than half the year. Most trace-gas budgets assume that trace-gas exchange stops when soil is snow covered or soil temperatures drop to ~0°C (refs 4,5). Thus alpine and sub-alpine soils are generally considered to be net sinks for atmospheric CO2. Some reports6,7, however, suggest that soil microorganisms beneath the snow continue to respire at temperatures close to 0 °C. Here we present evidence that the soils under alpine and sub-alpine snowpacks emit CO2 and N2O and take up atmospheric CH4 throughout the snow-covered period. These fluxes represent an important part of the annual trace-gas budget for these ecosystems.