Global methane emission through mud volcanoes and its past and present impact on the Earth's climate. Comment.

The role of mud volcanoes (MVs) as a source of methane(CH4) flux to the atmosphere and the ocean has been increasingly recognised in the last several years (Milkov
2000; Dimitrov 2002, 2003; Etiope and Klusman 2002; Kopf 2002, 2003; Milkov et al. 2003; Etiope and Milkov
2004). In one of the most recent papers, Kopf (2003) claims to report a reliable estimate of the global CH4 emission from MVs. However, the significance and
usefulness of the estimate presented by Kopf (2003) are rather poor. The used dataset is smaller than in previous
studies (although the author makes a reverse claim), and
some previously published works are misquoted and misinterpreted. Numerous arithmetic mistakes made
during simple calculations and data manipulations lead to confusing results and conclusions. In this comment,
we highlight some of the most significant problems with the estimates published by Kopf (2003).