Positive feedback & climate doom

Mike - your electronic feedback analogy is apt. As a biological scientist the feedback analogies I use are, for example, resource status and positive feedforward and negative feedback on populations (e.g. lemmings).  
 
In relation to metabolic control (balance, homeostasis by regulation of key enzymes or catalysts), specific biochemical pathways are often regulated by feedforward activation by excess of particular PRECURSOR metabolites of a key, \\\\\\\"allosterically\\\\\\\"-regulated enzyme catalyzing a key irreversible step (they bind to the enzyme and make it operate faster) - conversely excess concentrations of particular END PRODUCTS of the pathway often exert negative feedback (binding to the enzyme and inhibiting it, making it catalyze the reaction more slowly; end-product inhibition, feedback inhibition) ). 
 
Thus if we have a biochemical pathway involving the reversible (AB, CD) or irreversible (B->C) successive interconversions of metabolites (small chenmical compounds) and catalyzed, respectively, by enzymes E(AB), E(BC) and E(CD) then a higher concnetration of precursor A will activate E(BC) and make B->C go faster; conversely as the end product D increases it binds better to E(BC), inhibiting the enzyme and hence making B-> C go slower. 
 
An analogous process would be an industrial process of going from growing grapes to making wine - a grape glut would increase production (feedforward activation) and a wine glut would slow down production (feedback inhibition).  
 
Top UK climate scientist Professor James Lovelock FRS in discussing loss of this kind of oscillatory regulation - as described in his book \\\\\\\"The Revenge of Gaia\\\\\\\" - has used the analogy of a pleasure boat above Niagara Falls - the engines counteract the changes in current but if the engines slowly fail then it is remorselessly swept to its doom.  
 
A domestic thermostat and indeed our own 37 degrees Celsius physiological set-point system are further analogies.  
 
Some of the positive feedbacks in relation to the Arctic are crudelu summarized thus: global warming speeds up sea ice melting (e.g. to FINALLY overcome winter-summer feedback controls and oscillations and yield permanent no summer ice) -> white reflecting surface replaced by black light absorbing surface (the so-called \\\\\\\"albedo flip\\\\\\\") -> even more warming (positive feedback as opposed to homeostatic negative feedback) -> more loss, more warming -> increased Greenland air temperature -> increased loss of Greenland ice sheet -> increased lubrication of glaciers -> increased de-glaciation -> increased sea level -> -> goodbye London, New York, Bangkok, Calcutta, Dacca.

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