Wetlands are an important source of atmospheric methane (CH4), but the stre
ngth of this source and its sensitivity to potential changes in climate are
still uncertain. In this study, continuous measurements from 1990 to 1998
of atmospheric CH, from the Canadian observational sites at Fraserdale (49
degrees 53'N 81 degrees 34'W) and Alert (82 degrees 27'N 62 degrees 31'W) a
re used to estimate CH, emissions from the Hudson Bay Lowland (HBL), a 320,
000 km(2) semicontinuous wetland region in central Canada. The HBL comprise
s similar to 10% of the total area of northern wetlands. A conceptually sim
ple approach was used to calculate the methane emission flux using the CH4
concentration difference between Alert and Fraserdale, the residence time o
f the air mass over the HBL, and the mixing height of the convective bounda
ry layer. Emission rates estimated using this approach for 1990 compare wel
l with empirical aircraft and tower flux measurements made within the HBL d
uring the same time period, thus indicating that the methodology used is re
asonable. Annual CH4 emission rates range from 0.23 to 0.50 Tg CH4 yr(-1) a
nd are much lower than many empirical flux measurements observed at other n
orthern wetland sites. A seasonal temperature sensitivity with a Q(10) of a
bout 4 was found. Moreover, the observed interannual variations in emission
s are well correlated to variations in annual air temperatures correspondin
g to a sensitivity of Q(10) approximate to 7. That is, a 10 degrees C chang
e in annual temperature would result in a sevenfold change in wetland emiss
ions which is much larger than Q(10) values used in current global CH4 mode
ls (typically Q(10) approximate to 1.5). Our findings suggest that northern
wetland emissions are probably overestimated to date but may increase sign
ificantly due to predicted global warming.