Quantitative cross-sectoral impact assessments for differing scenarios are not yet available for Australia and New Zealand. Regional impacts will vary nonlinearly with time before and after stabilization of GHG concentrations. Warming will continue to increase after stabilization, but the beneficial effects of CO₂ on plants will no longer increase. Moreover, regional patterns of rainfall change, particularly in southern Australian and New Zealand areas, will tend to reverse after stabilization of GHGs (see Section 12.1.5.1). These complexities, together with the continuing post-stabilization rise in sea level, mean that estimated impacts at the time of stabilization may not be sufficient to determine whether the level of stabilization is a safe one.

Given that some of the climate sensitivities listed in Section 12.9.6, and especially in Table 12-2, already have been observed for natural climate variations (such as El Niño), confidence is high that a range of impacts will occur in Australia and New Zealand as a result of climate change over the coming decades. This level of certainty, and the possibility that the early stages of greenhouse-related changes already may be occurring, justify prudent risk management through initiation of appropriate mitigation and adaptation strategies. Probabilistic assessments of risk, which account for the uncertainties, are regarded as a way forward. These assessments attempt to quantify the various sources of uncertainty to provide a conditional probability of climate change that would cause critical system performance thresholds to be exceeded and require adaptation or result in losses. Stakeholders may define their own subjective levels of acceptable risk and plan accordingly to adapt before or when the threshold is exceeded. Some examples for Australia and New Zealand are presented in this chapter (see Sections 12.5.2, 12.6.1, 12.8.2, and 12.8.4), but more are needed.

The key regional concerns identified in this chapter regarding vulnerability to climate change impacts are ecosystem uniqueness, isolation, and vulnerability; agricultural commodities and terms of trade; droughts, floods, and water supply; increased coastal and tropical exposure to climate hazards; impacts on indigenous peoples and their involvement in adaptation planning; coral reefs; and Australian alpine areas.

Major expected impacts, vulnerability, and adaptability are summarized in Table 12-2. Note that although Australian and (to a lesser extent) New Zealand farmers have adapted, at least in part, to existing El Niño-related droughts, they depend on good years for recovery. Thus, despite their adaptability, they are quite vulnerable to any increase in the frequency of drought or to a tendency for droughts to last for a longer period. This vulnerability flows through to the rural communities that service them (see Section 12.5.6).

Several of these vulnerabilities are likely to interact synergistically with each other and with other environmental stresses. Moreover, vulnerability is a result of exposure to hazard and capacity to adapt. Thus, vulnerability will be greatly affected by future changes in demography, economic and institutional capacity, technology, and the existence of other stresses.

There have been no rigorous studies for Australia or New Zealand that have taken all of these variables into account. Thus, Table 12-2 is based largely on studies that assume that the society that is being impacted is much like that of today. It should not be assumed, however, that socioeconomic changes in the future necessarily will reduce vulnerability in Australia and New Zealand. Indeed, many existing socioeconomic trends may exacerbate the problems. For instance, the bias toward population and economic growth in coastal areas, especially in the tropics and subtropics, by itself will increase exposure to sea-level rise and more intense tropical cyclones. If such trends are not to increase vulnerability, they will need to be accompanied by a conscious process of planning to reduce vulnerability by other means (e.g., changes in zoning and engineering design criteria). Thus, vulnerability estimates are based on present knowledge and assumptions and can be changed by new developments, including planned adaptation.

Table 12-2: Main areas of vulnerability and adaptability to climate change impacts in Australia and New Zealand. Degree of confidence that tabulated impacts will occur is indicated by a letter in the second column (VH = very high, H = high, M = medium, L = low, VL = very low). These confidence levels, and the assessments of vulnerability and adaptability, are based on information reviewed in this chapter and assume continuation of present population and investment growth patterns.
Sector	Impact	Vulnerability	Adaptation	Adaptability	Section
Hydrology and water supply	- Irrigation and metropolitan supply constraints, increased salinization—H	High in some areas	- Planning, water allocation, and pricing	Medium	12.3.1, 12.3.2
	- Saltwater intrusion into some island and coastal aquifers—H	High in limited areas	- Alternative water supplies, retreat	Low	12.3.3
Terrestrial ecosystems	- Increased salinization of dryland farms and some streams (Australia)—M	High	- Changes in land-use practices	Low	12.3.3
	- Biodiversity loss, notably in fragmented regions, Australian alpine areas, and southwest of WA—H	Medium to high in some areas	- Landscape management; little possible in alpine areas	Medium to low	12.4.2, 12.4.4, 12.4.8
	- Increased risk of fires—M	Medium	- Land management, fire protection	Medium	12.1.5.3, 12.5.4, 12.5.10
	- Weed invasion—M	Medium	- Landscape management	Medium	12.4.3
Aquatic ecosystems	- Salinization of some coastal freshwater wetlands—M	High	- Physical intervention	Low	12.4.7
	- River and inland wetland ecosystem changes—M	Medium	- Change water allocations	Low	12.4.5, 12.4.6
	- Eutrophication—M	Medium in inland Aus. waters	- Change water allocations, reduce nutrient inflows	Medium to low	12.3.4
Coastal ecosystems	- Coral bleaching, especially Great Barrier Reef—H	High	- Seed coral?	Low	12.4.7
	—More toxic algal blooms?—VL	Unknown	—	—	12.4.7
Agriculture, grazing, and forestry	- Reduced productivity, increased stress on rural communities if droughts increase, increased forest fire risk—M	Location-dependent, worsens with time	- Management and policy changes, fire prevention, seasonal forecasts	Medium	12.5.2, 12.5.3, 12.5.4
	- Changes in global markets as a result of climate changes elsewhere—H, but sign uncertain	High, but sign uncertain	- Marketing, planning, niche and fuel crops, carbon trading	Medium	12.5.9
	- Increased spread of pests and diseases—H	Medium	- Exclusion, spraying	Medium	12.5.7
	- Increased CO2 initially increases productivity, but offset by climate changes later—L	Changes with time	- Change farm practices, change industry		12.5.3, 12.5.4
Horticulture	- Mixed impacts (+ and -), depends on species and location—H	Low overall	- Relocate	High	12.5.3
Fish	- Recruitment changes (some species)—L	Unknown net effect	- Monitoring, management	—	12.5.5
Settlements and industry	- Increased impacts of flood, storm, storm surge, sea-level rise—M	High in some places	- Zoning, disaster planning	Moderate	12.6.1, 12.6.4
Human health	- Expansion and spread of vector-borne diseases—H	High	- Quarantine, eradication, or control	Moderate to high	12.7.1, 12.7.4
	- Increased photochemical air pollution—H	Moderate (some cities)	- Emission controls	High	12.7.1

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