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EXECUTIVE SUMMARY
The Australia and New Zealand Region: This region spans the tropics to
mid-latitudes and has varied climates and ecosystems, including deserts, rainforests,
coral reefs, and alpine areas. The climate is strongly influenced by the surrounding
oceans. The El Niño-Southern Oscillation (ENSO) phenomenon leads to floods
and prolonged droughts, especially in eastern Australia and parts of New Zealand.
The region therefore is sensitive to the possible changes toward a more El Niño-like
mean state suggested by Working Group I. Extreme events are a major source of
current climate impacts, and changes in extreme events are expected to dominate
impacts of climate change. Return periods for heavy rains, floods, and storm surges
of a given magnitude at particular locations would be modified by possible increases
in intensity of tropical cyclones, mid-latitude storms, and heavy rain events
(medium confidence) and changes in the location-specific frequency of tropical
cyclones (low to medium confidence). Scenarios of climate change based on recent
coupled atmosphere-ocean climate models suggest that large areas of mainland Australia
will experience significant decreases in rainfall during the 21st century (low
to medium confidence).
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 impacts—notably, 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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