Australasia is defined here as Australia, New Zealand, and their outlying tropical and mid-latitude islands. Australia is a large, relatively flat continent reaching from the tropics to mid-latitudes, with relatively nutrient-poor soils, a very arid interior, and rainfall that varies substantially on seasonal, annual, and decadal time scales, whereas New Zealand is much smaller, mountainous, and mostly well-watered. The ecosystems of both countries contain a large proportion of endemic species, reflecting their long evolutionary history and isolation from other land masses. They have been subject to significant human influences, before and after European settlement 200 years ago.

The region's climate is strongly influenced by the surrounding oceans. Key climatic features include tropical cyclones and monsoons in northern Australia; migratory mid-latitude storm systems in the south, including New Zealand; and the ENSO phenomenon, which causes floods and prolonged droughts, especially in eastern Australia.

The total land area is 8 million km², and the population is approximately 22 million. Much of the region is very sparsely populated; most people (85%) live in a relatively small number of coastal cities and towns. Both countries have significant populations of indigenous peoples who generally have lower economic and health status. The two countries have developed economies and are members of the Organisation for Economic Cooperation and Development (OECD); unlike other OECD countries, however, their export trade is dominated by commodity-based industries of agriculture and mining.

The Australasian chapter (Basher et al., 1998) of the IPCC Special Report on Regional Impacts of Climate Change (RICC) (IPCC, 1998) provides an extensive assessment of likely climate change impacts and adaptation options for Australia and New Zealand, based on work published until early 1998. That report concludes that Australia's relatively low latitude makes it particularly vulnerable through impacts on its scarce water resources and crops that presently are growing near or above their optimum temperatures, whereas New Zealand—a cooler, wetter, mid-latitude country—may gain some benefit from the ready availability of suitable crops and a likely increase in agricultural production with regional warming. Nevertheless, a wide range of situations in which vulnerability was thought to be moderate to high were identified for both countries—particularly for ecosystems, hydrology, coastal zones, settlements and industry, and health. Indirect local impacts from possible climatically driven changes in international conditions—notably commodity prices and international trade—also was identified as a major issue in the 1998 report, as well as by the New Zealand Climate Change Programme (1990). Key points from Basher et al. (1998) follow.

Climate and Climate Trends: Climate trends were reported to be consistent with those in other parts of the world, with mean temperature increases of as much as 0.1°C per decade over the past century, a faster increase in nighttime than daytime temperatures, and sea level rising an average of about 20 mm per decade over the past 50 years. Increases in average rainfall and the frequency of heavy rainfalls were reported for large areas of Australia.

Climate Scenarios: Australian scenarios reported for 2030 exhibited temperature increases of 0.3-1.4°C, uncertain overall rainfall decrease of as much as 10%, and more high-intensity rainfall events. Projected changes for 2070 were about twice the 2030 changes. New Zealand projections included similar temperature increases, as well as stronger westerly air flow, with resulting precipitation increases in the west and decreases in the east.

Water Supply and Hydrology: Possible overall reduction in runoff, with changes in soil moisture and runoff varying considerably from place to place but reaching as much as ±20%, was suggested for parts of Australia by 2030. Sharpened competition was expected among water users, with the large Murray-Darling Basin river system facing strong constraints. Enhanced groundwater recharge and dam-filling events were expected from more frequent high-rainfall events, which also were expected to increase flooding, landslides, and erosion. A reduced snow season was expected to decrease the viability of the ski industry, although it would provide seasonally smoother hydroelectricity generation in New Zealand.

Ecosystems and Conservation: Significant potential impacts identified on Australasian land-based ecosystems included alteration in soil characteristics, water and nutrient cycling, plant productivity, species interactions, and ecosystem composition and function, exacerbated by any increases in fire occurrence and insect outbreaks. Aquatic systems would be affected by changes in runoff, river flow, and associated transport of nutrients, wastes, and sediments. These changes and sea-level rise would affect estuaries and mangroves. Australia's coral reefs were considered to be vulnerable to temperature-induced bleaching and possibly to sea-level rise and weather change.

Food and Fiber: Direct impacts on agriculture from CO₂ increases and climate changes were expected to vary widely in space and time, with perhaps beneficial effects early in the 21st century, followed by more detrimental effects in parts of Australia as warming increases. Any changes in global production and hence international food commodity prices would have major economic impacts. The net impact on production forestry from changes in tree productivity, forest operational conditions, weeds, disease, and wildfire incidence was not clear. The impact on fisheries could not be confidently predicted.

Settlements and Industry: Possible changes were noted in the frequency and magnitude of climatic "natural disaster" events affecting economically important infrastructure. Likely impacts of climate change were identified on water and air quality, water supply and drainage, waste disposal, energy production, transport operations, insurance, and tourism.

Human Health: Increases were expected in heat-stress mortality (particularly in Australia), the incidence of tropical vector-borne diseases such as dengue, and urban pollution-related respiratory problems.

Adaptation Potential and Vulnerability: Some of the region's ecosystems were identified as very vulnerable, with fragmentation and alteration of landscape by urban and agricultural development limiting natural adaptability. Land-use management was the primary adaptation option identified. Although coral reefs were identified as vulnerable, it was suggested that they might be able to keep pace with sea-level rise.

Techniques that already provide considerable adaptability of agriculture to existing climate variability may apply to climate change over the next few decades. However, at longer time horizons the climate was expected to become less favorable to agricultural production in Australia, leading to increased vulnerability. Scientifically based integrated fisheries and coastal zone management were regarded as principal adaptation options for fisheries.

Adaptation options identified for settlements and infrastructure included integrated catchment management, changes to water pricing systems, water efficiency initiatives, building or modifying engineering structures, relocation of buildings, and urban planning and management. Low-lying coastal settlements were regarded as highly vulnerable to high sea level and storm events. Adaptation options included integrated coastal zone management (ICZM); redesign, rebuilding, or relocation of capital assets; and protection of beaches and dunes. New Zealand is exposed to impacts on its Pacific island territories, including the eventual possibility of having to accept environmental refugees.

A moderate degree of vulnerability was identified for human health, with adaptation responses including strengthening existing public health infrastructure and meeting the needs of vulnerable groups such as isolated communities and the poor.

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