Before stabilization of greenhouse gas (GHG) concentrations, the north-south temperature gradient in mid-southern latitudes is expected to increase (medium to high confidence), strengthening the westerlies and the associated west-to-east gradient of rainfall across Tasmania and New Zealand. Following stabilization of GHG concentrations, these trends would be reversed (medium confidence).
Water Supply and Hydrology: In some areas, water resources already are stressed and are highly vulnerable, with intense competition for water supply. This is especially so with respect to salinization (parts of Australia) and competition for water between agriculture, power generation, urban areas, and environmental flows (high confidence). Increased evaporation and possible decreases of rainfall in many areas would adversely affect water supply, agriculture, and the survival and reproduction of key species in parts of Australia and New Zealand (medium confidence).
Ecosystems and Conservation: Warming of 1°C would threaten the survival of species currently growing near the upper limit of their temperature range, notably in some Australian alpine regions that already are near these limits, as well as in the southwest of western Australia. Other species that have restricted climatic niches and are unable to migrate because of fragmentation of the landscape, soil differences, or topography could become endangered or extinct. Other ecosystems that are particularly threatened by climate change include coral reefs (Australia) and freshwater wetlands in the coastal zone and inland.
Food and Fiber: Agricultural activities are particularly vulnerable to regional reductions in rainfall in southwest and inland Australia (medium confidence) and eastern New Zealand. Drought frequency and consequent stresses on agriculture are likely to increase in parts of Australia and New Zealand as a result of higher temperatures and possibly more frequent El Niños (medium confidence). Enhanced plant growth and water-use efficiency (WUE) resulting from carbon dioxide (CO2) increases may provide initial benefits that offset any negative impacts from climate change (medium confidence), although the balance is expected to become negative with warmings in excess of 2-4°C and associated rainfall decreases (medium confidence). Reliance on exports of agricultural and forest products makes the region sensitive to changes in commodity prices induced by changes in climate elsewhere.
Australian and New Zealand fisheries are influenced by the extent and location of nutrient upwellings governed by prevailing winds and boundary currents. In addition, ENSO influences recruitment of some fish species and the incidence of toxic algal blooms. There is as yet insufficient knowledge about impacts of climate changes on regional ocean currents and about physical-biological linkages to enable confident predictions of changes in fisheries productivity.
Settlements, Industry, and Human Health: Marked trends to greater population and investment in exposed coastal regions are increasing vulnerability to tropical cyclones and storm surges. Thus, projected increases in tropical cyclone intensity and possible changes in their location-specific frequency, along with sea-level rise, would have major impactsnotably, increased storm-surge heights for a given return period (medium to high confidence). Increased frequency of high-intensity rainfall would increase flood damages to settlements and infrastructure (medium confidence). There is high confidence that projected climate changes will enhance the spread of some disease vectors, thereby increasing the potential for disease outbreaks, despite existing biosecurity and health services.
Vulnerability and Adaptation: Climate change will add to existing stresses on achievement of sustainable land use and conservation of terrestrial and aquatic biodiversity. These stresses include invasion by exotic animal and plant species, degradation and fragmentation of natural ecosystems through agricultural and urban development, dryland salinization (Australia), removal of forest cover (Australia and New Zealand), and competition for scarce water resources. Within both countries there are economically and socially disadvantaged groups of people, especially indigenous peoples, that are particularly vulnerable to additional stresses on health and living conditions induced by climate change. Major exacerbating problems include rapid population and infrastructure growth in vulnerable coastal areas, inappropriate use of water resources, and complex institutional arrangements. Adaptation to climate change, as a means of maximizing gains and minimizing losses, is important for Australia and New Zealand but is relatively little explored. Options include improving water-use efficiency and effective trading mechanisms for water; more appropriate land-use policies; provision of climate information and seasonal forecasts to land users, to help them manage for climate variability and change; improved crop cultivars; revised engineering standards and zoning for infrastructure development; and improved biosecurity and health services. Such measures often will have other benefits, but they also may have costs and limits.
Integrated Assessments: Comprehensive cross-sectoral estimates of net climate change impact costs for various GHG emission scenarios, as well as for different societal scenarios, are not yet available. Confidence remains very low in the previously reported (Basher et al., 1998) estimate for Australia and New Zealand of -1.2 to -3.8% of gross domestic product for an equivalent doubling of CO2 concentrations. This out-of-date estimate did not account for many currently identified effects and adaptations.
Summary: Australia has significant vulnerability to changes in temperature and precipitation projected for the next 50-100 years (very high confidence) because it already has extensive arid and semi-arid areas and lies largely in the tropics and subtropics. New Zealand, a smaller and more mountainous country with a generally more temperate maritime climate, may be more resilient to climate changes than Australia, although considerable regional vulnerability remains (medium confidence).
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