Feedback mechanisms in changing systems are poorly understood. These mechanisms could produce a series of downstream effects as conditions within a system deviate from "normal" and can include mechanisms that bring conditions back toward "normal" (correcting) or push conditions further away from "normal" (compounding). Feedback of interactions between humans and the environment in the face of climate change are likely to be negative and are expected to increase. As humans have to take adaptive actions to preserve their systems in the face of climate change and sea-level rise, there is a risk that impacts on the environment will increase, despite better awareness of the issues. The short-term needs of humans are likely to take precedence over longer-term needs, which are intimately tied up with the environment. This could mean greater-than-expected and unpredictable indirect impacts resulting from climate change and sea-level rise.

Small island states urgently need sensible predictive information and tools for minimizing the likely outcomes of climate change and sea-level rise because it is now generally accepted that small islands are intrinsically more vulnerable than larger countries (Briguglio, 1992, 1993, 1995, 1997; Wells, 1996, 1997; Atkins et al., 1998; UNDP, 1998). The vulnerability of natural systems is still under investigation, although work is underway (Yamada et al., 1995; Sem et al., 1996; Kaly et al., 1999). This makes the requirement for information and tools for generating such information a top priority. The outcome of climate change on human and natural systems in small island states will depend on changes induced by climate itself, feedback mechanisms, human adaptive capacity, and the resilience of biophysical and human systems.

Indicators of high resilience might include the presence of healthy, intact ecosystems; the ability of species to acclimatize to new temperature regimes; the presence of land higher than the maximum predicted transgression plus storm surges; high productivity; reproduction and recruitment of species; and high rates of natural recovery (Kaly et al., 1999).

Resilience refers to the innate ability of biophysical and human systems to maintain their integrity when subjected to disturbance (Holling, 1973; Ludwig et al., 1997). For most natural systems, knowledge of resilience to climate change and sea-level rise is inadequate. For example, there are insufficient data to describe the ability of a reef to withstand sea-level rise of 20-40 cm over the next 50 years (but see Hoegh-Guldberg, 1999). Predicting which ecological variables (e.g., species, processes) might be affected and what effect this would have on ecosystem diversity, function, and future resilience may be difficult or impossible (Lubchenco et al., 1993). Proxy estimates have been made, most notably using recent El Niño events in the eastern Pacific; these estimates have many of the expected effects of climate change (Castilla et al., 1993; Burns, 2000). For oceans, these and other proxy estimates predict the extinction of species, mass mortality and bleaching of corals, changes in the geographic range of species, increases in disease, unexpected predation, decreases in productivity, and increases in harmful algal blooms (Glynn, 1984, 1988, 1991; Bak et al., 1984; Hallegraeff, 1993; Lessios, 1998; Hoegh-Guldberg, 1999).

Although earlier work suggested that systems exposed to perturbations tend to have greater capacity to recover from shock (e.g., Holling, 1973), research in a small island context challenges this conventional wisdom. Kaly et al. (1999) demonstrate that for many systems, the greater the number and intensity of hazards (human-induced as well as natural) that have impacted them in the past, the greater is their level of vulnerability to future stresses. Furthermore, because neither the natural resilience nor the altered resilience of any ecosystem is known—let alone the resilience that might arise as a result of summed or interactive effects—it is impossible to directly estimate overall resilience. This finding is very disturbing for most small island states, where ecosystems already are severely stressed from natural and anthropogenic forces.

17.4.2.1. Inconsistencies and Limitations in Projected Changes

Present ability to accurately assess the effects of climate change in small island states, as in other regions, is further impeded by conflicting predictions of how natural systems may respond. For example, some studies cite the responses of ecosystems to El Niño events in the 1980s and 1990s as indicative of the likely effects of climate change, with conflicting outcomes (Salinger, 1999; Gillespie and Burns, 2000; Hay, 2000). On one hand, it is expected that primary productivity in oceans will decrease as a result of global warming when upwelled waters become shoaled (Roemmich and McGowan, 1995; Barber et al., 1996). On the other hand, it has been predicted that harmful algal blooms will increase with increasing temperatures (Colwell, 1996; Nurse et al., 1998; see also Hales et al., 1999b). Clearly, forecasting of likely outcomes will be more complex than may have been expected initially. Thus, planning of appropriate responses in regions of low adaptive capacity, such as small island states, presents an even greater challenge.

17.4.2.2. Ecosystem Collapse

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