Current global warming has been linked to anthropogenic greenhouse gas (GHG) concentration increases. Environmental and animal factors affect and lend uncertainties to GHG emissions from swine manure. A micrometeorological four-tower mass balance method was used to quantify CH4 and N 2O emissions from stored liquid swine manure in a quasi-continuous year-round study at two commercial swine farms (Jarvis and Guelph) in a cold climate region. Data filtering criteria were developed to minimize errors in flux calculation, and were efficient to improve accuracy of GHG flux estimates. In the Jarvis experiment, CH4 and N2O emissions were significantly higher than zero, with emissions during summer higher than during fall (CH4: 583.8 vs. 174.1 [mu]g/m2/s; N 2O: 337.6 vs. 101.8 ng/m2/s). In the Guelph experiment, only CH4 emissions were significantly larger than zero (1054.8 in fall vs. 22.7 [mu]g/m2/s in winter). Significant differences in daytime and nighttime CH4 fluxes were observed during summer and winter. Each manure storage tank was very heterogeneous, showing 'hot spots' emitting higher CH4. Methane fluxes calculated through IPCC default methods were 1.6 to 6.7 times higher than measured via four-tower mass balance method.