What was done
The authors, in their words, "used remote sensing, aerial surveys and year-round, continuous measurements of CH4 flux to (1) quantify CH4 emissions from north Siberian lakes, paying particular attention to the role of ebullition, and (2) document the role of thermokarst erosion as a landscape process that fuels CH4 production and feeds back to climate warming."

What was learned
Walter et al. say that ebullition, or bubbling, accounts for 95% of methane emissions from Siberia's thaw lakes, and that the methane flux from the lakes in their study region may be five times higher than previously estimated by random measurements that failed to properly account for the bubbling phenomenon. They also state that they "have linked the expansion of thaw lakes during recent decades with a 58% increase in lake CH4 emissions, demonstrating a new feedback to climate warming," or as they say in another place, "regional warming observed during the study period of 1974-2004 is consistent with lake expansion that contributed to rising atmospheric CH4 concentrations and global temperature."

What it means
Although these statements sound ominous, and have generally been reported as such in the popular press, the five researchers are careful to state in the concluding paragraph of their paper that the recent increase in CH4 flux due to lake expansion "is modest relative to anthropogenic emissions." Indeed, it is so small compared to the sum of everything else impacting the atmosphere's CH4 concentration that rather than rising at a gradually increasing rate as the earth has warmed in recent decades, the air's CH4 content has actually been rising at a gradually decreasing rate (see, for example, our review of the study of Simpson et al., 2000). What is more, this decreasing rate-of-rise has dropped to the point where for the last several years there has been little to no increase at all in the air's CH4 concentration (see our review of the study of Dlugokencky et al., 2003). Hence, it would appear that the angst the paper has aroused in some circles is little more than a tempest in a teapot.

References
Dlugokencky, E.J., Houweling, S., Bruhwiler, L., Masarie, K.A., Lang, P.M., Miller, J.B. and Tans, P.P. 2003. Atmospheric methane levels off: Temporary pause or a new steady-state? Geophysical Research Letters 30: 10.1029/2003GL018126.

Simpson, I.J., Blake, D.R. and Rowland, F.S. 2002. Implications of the recent fluctuations in the growth rate of tropospheric methane. Geophysical Research Letters 29: 10.1029/2001GL014521.