Run Away!

clipped from www.coyoteblog.com Yet it is reliably inferred from palaeoclimatological data that no “runaway greenhouse effect” has occurred in the half billion years since the Cambrian era, when atmospheric CO2 concentration peaked at almost 20 times today’s value Positive feedback can be weird and unstable.  If there is enough of it, processes tend to run away (e.g. nuclear fission), Most scientists, when then meet a new process, would probably assume negative feedback until proven otherwise.  This is a particular issue in climate, where folks like Michael Mann have gone out of their way to argue that the world temperature history over the last 1000 years before man began burning fossil fuels is incredibly stable and unchanging.  If so, how can this be consistent with strong positive feedback?