At the start of the industrial revolution,
amplifying feedbacks were non-operative.
Small man-made changes in climate could easily be reversed by man-made
intervention. The power of positive
feedback relative to the power of human control was negligible. As global heating increased and global warming became detectable, positive feedbacks were mobilised, gaining power relative to the human capacity for intervention. Eventually the positive feedback process takes control and all further effect of emissions reduction is nullified. The critical threshold at which this takes place represents the closing of the window of opportunity during which human initiatives to generate negative (system-damping) interventions are still able to halt global warming and return it to a stable, life-sustaining, equilibrium. The more powerful the positive feedback loops become, the more massive and costly is the intervention needed to return the system to equilibrium. As the energy exchange approaches the critical threshold, the power ratio between positive feedback and controlling intervention (and the total cost of making an effective intervention) reaches a vertical asymptote. In other words it approaches infinity. Beyond that critical threshold in global heating there is no further intervention capable of damping the system. The runaway chain-reaction of uncontrollable climate change will have been initiated, leading inevitably to the sixth or "Anthropocene" extinction event.  Pre-industrial accumulation of human-generated GHGs just cancelled out the natural damping negative feedback system, leaving the earth in balance in a condition of unstable equilibrium. Exponential increase in GHG concentration driven by the industrial revolution then tipped the system over the top of the hill and into the present state of accelerating climate change. The effects of human-generated emissions are being amplified by an increasingly powerful set of positive feedback mechanisms. The further we move away from the position of unstable equilibrium, the more powerful the positive-feedback system becomes, and the faster is the resultant rate of climate change. |