Feedback Dynamics and the Acceleration of Climate Change: An Update of the Scientific Analysis


The Meridian Programme, March 2006

 

Description

 

The paper reports a profound shift that has happened recently in the scientific understanding of the behaviour of the earth’s climate system as a whole and explains why this is a cause for concern.


Contents

  • Time delays and systems-thinking
  • Basic drivers of climate change
  • Feedbacks operating in the climate system
  • Strong feedbacks and the acceleration of climate change
  • The concept of “critical threshold”
  • A landscape presentation of climate dynamics
  • Climate stabilisation: Required intervention strategy

Summary

 

The document starts with several quotes from leading climate scientists. These capture the report’s overall message: the speed of climate change is increasing, society’s window of opportunity to affect the process is closing and we are close to uncontrollable climate change.


Time-delays and systems-thinking. It takes a long time to raise the temperature of the earth as a whole: there is a time-delay between cause and effect of over half a century. All climate change impacts so far are from the 0.7°C rise in temperature to-date, which represents the effects of GHG concentrations reached in about 1960. Even if emissions were to be immediately stabilised, effects will still quadruple.


Basic drivers of climate change. Different elements drive climate change, including, for example, solar and geo-thermal energy, CO2 concentration and the albedo effect (reflection of solar energy back into space, for example by ice). Human additions of CO2 to the climate system create an imbalance. The standard model says that the surface temperature will eventually rise to a new, higher, equilibrium.


Feedbacks operating in the climate system. Eight categories of feedback mechanism are identified. Each affects both its own functions and the driver conditions for others. The four main subsystems are: carbon, albedo, methane and water-vapour. Most systems are now in net positive feedback, creating an interactive set of mutually-reinforcing subsystems. This ‘second-order’ feedback system therefore accelerates climate change. Existing models are therefore likely to be underestimating the problem.


Strong feedbacks and the acceleration of climate change. The major feedback mechanisms that accelerate climate change and reinforce each other are: degradation of the carbon sink; emission of non-anthropogenic CO2; increasing atmospheric water-vapour; the ice-albedo effect; and release of stored methane. For example, water vapour is easily the most influential GHG, but its effect on change has so far been limited because temperatures have remained close to equilibrium. A higher temperature could lead to much more water vapour, with significant consequences.


Concept of critical thresholds. This is the point at which the positive feedback takes control, and all further human emissions reductions efforts become futile. This represents the closing of humans’ window of opportunity to act on climate change. Beyond the critical threshold, runaway climate change will happen, leading to ever-increasing temperatures and an “anthropocene” mass-extinction event.


A landscape presentation of climate dynamics. Using the metaphor of the watershed in a landscape to illustrate climate dynamics, the report warns that we are in the early stages of runaway climate change.


Climate stabilisation. Several strategy recommendations and policy suggestions are made.

 

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