10.8.2 Confidence levels and unknowns

The vulnerability of key sectors to the projected climate change for each of the seven sub-regions of Asia based on currently available scientific literature referred to in this assessment have been assigned a degree of confidence which is listed in Table 10.11. The assigned confidence levels could provide guidance in weighing which of the sectors ought to be the priority concerns based on the most likely future outcomes. However, some of the greatest concerns emerge not from the most likely future outcomes but rather from possible ‘surprises’. Growing evidence suggests the ocean-atmosphere system that controls the world’s climate can lurch from one state to another, such as a shutdown of the ‘ocean conveyor belt’ in less than a decade. Certain threshold events may become more probable and non-linear changes and surprises should be anticipated, even if they cannot be predicted with a high degree of confidence. Abrupt or unexpected changes pose great challenges to our ability to adapt and can thus increase our vulnerability to significant impacts (Preston et al., 2006).

The spotlight in climate research is shifting from gradual to rapid or abrupt change. There is some risk that a catastrophic collapse of the ice sheet could occur over a couple of centuries if polar water temperatures warm by a few degrees. Scientists suggest that such a risk has a probability of between 1 and 5% (Alley, 2002). Because of this risk, as well as the possibility of a larger than expected melting of the Greenland Ice Sheet, a recent study estimated that there is a 1% chance that global sea level could rise by more than 4 metres in the next two centuries (Hulbe and Payne, 2001).