Methane is usually released when the ocean temperature rises and the methane ice "melts" into gas. It's one of the theories for the losses in the Bermuda Triangle, as it could also affect planes in some circumstances. It sounds better than a mysterious curse to me.

In the geological record, periods of significant global warming are linked to methane release events. The temperature rises enough to cause a major release, then the effects cause a big spike in global temperature. Rinse & repeat. Not a happy thought given that we are living through the hottest years on record now, and no one sure how hot it would have to get and for how long to trigger a major methane release.