The Statistical Nature of Climate Change

While the concept of climate change may connote modifications to something steady and immutable, climate in fact varies on a number of scales. Human activities as well as natural systems evolve in response to such variations and can cope with a range of climatic conditions without serious damage. Figure 1.1 conceptualizes current climate variations and the coping range. Occasionally, climate variations exceed the coping range and the system is put under higher stress or severely damaged.  If the frequency of such events is low, the system will progressively recover. When they become more frequent, the system may reach a new state. Within such a framework, climate change means that severe impact events may happen more frequently, and/or events of unprecedented magnitude may occur, putting the system under such stress that recovery is difficult if not impossible (see figure 1.1). 

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Figure 1.1 Conceptual illustration of historical and future climate, coping range and adaptation. Source: Lu, 2007, adapted from Carter et al. 2007.
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Figure 1.2 The effect of changes in temperature distribution on extremes. Different changes in temperature distributions between present and future climate and their effects on extreme values of the distributions: (a) effects of a simple shift of the entire distribution toward a warmer climate; (b) effects of an increase in temperature variability with no shift in the mean; (c) effects of an altered shape of the distribution, in this example a change in asymmetry toward the hotter part of the distribution. Source: IPCC (2012)

Adaptation is aimed at limiting damage and speeding recovery from such damaging events. As seen in figure 1.2, high impact events in the future can occur more frequently due to:

  • Change in the average, keeping the amplitude of the variability the same (Fig. 1.2a) 
  • Change in the amplitude of the variability, keeping the average the same (Fig. 1.2b)
  • Change in the frequency of rare events on one side of the distribution (Fig. 1.2c)
  • Any combination of the above at the same time.

 

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