CLIMATE CHANGE IMPACTS ON NEW ZEALAND – EXECUTIVE SUMMARY
This report examines the likely impacts of climate change and global warming on New Zealand, based on expert re-ports
and peer-reviewed scientific studies, published internationally and in New Zealand. It does not attempt to provide a
comprehensive summary, but updates the last gov-ernment-led assessment of climate change impacts carried out in 1990 and
concentrates on areas where new knowledge has been gained over the last decade.
Scientific basis and global impacts of climate change
A broad range of observations shows that the world has warmed during the 20th century. There is now stronger evi-dence
that most of the warming observed over the last 50 years is attributable to human activities, namely the emission of
This report uses two emission scenarios to assess future cli-mate change and its impacts. Scenario 1 assumes no attempts
to control greenhouse gas emissions, while scenario 2 as-sumes that steps are taken to stabilise the atmospheric
concentration of carbon dioxide and to limit emissions of the other major greenhouse gases methane and nitrous oxide.
Neither scenario is a prediction or represents a policy target; both serve only to answer "what-if" questions.
Climate models predict a global warming by 2100 between 2.1 and 3.8 degrees Celsius for scenario 1 and between 1.4 and
2.6 degrees Celsius for scenario 2, compared to an ob-served warming of about 0.6 degrees Celsius during the 20th
Global impacts of climate change, particularly on world markets and developing countries, will have repercussions for
New Zealand. However because very few clear predic-tions of these indirect effects can be made at this stage, this
report focuses on the impacts of local climate change in New Zealand.
Projected New Zealand climate changes
Temperatures in New Zealand are likely to increase faster in the North Island than in the South Island, but generally
less than global average temperatures. Rainfall is projected to increase in the west of the country and decrease in many
eastern regions. While these general trends are considered relatively robust findings, the magnitude of the projected
changes depends on the global greenhouse gas emission sce-nario and also varies considerably between different climate
models, particularly for local rainfall patterns.
Quantitative regional climate projections are more likely to undergo revision in future assessments than global
projec-tions. Comprehensive impact assessments in which rainfall is a key component therefore need to incorporate a
range of dif-ferent scenarios of regional climate change, even for a single given global warming assumption.
Under the projected reductions of average rainfall in eastern areas and higher temperatures, dry periods will increase
in some regions. Models suggest that at the same time, extremely heavy rain-fall events could become more frequent in
many areas, increasing the risk of flooding and erosion. No predictions about frequency and intensity of mid-latitude
storms are cur-rently available.
Many climate models indicate a greater future variability of rainfall with an increased risk of droughts, but no
quantita-tive predictions are possible at this stage. Other expected changes in climate extremes are, on average, fewer
frost days during winter and more hot days during summer.
Sea-level rise and coastal processes
Sea levels are expected to rise under global warming, but sci-entific uncertainties are large. Global sea levels are
estimated to rise between 9 and 88 cm by 2100 under global warming, with ranges from 13 to 70 cm for scenario 1 and from
9 to 53 cm for scenario 2. During the 20th century global sea levels rose on average between 10 and 20 cm.
A quantitative assessment of the impact of rising sea levels on New Zealand coasts is difficult. Major earthquakes can
lead to local changes in land elevation which can override the effect of a gradual sea-level rise. In addition,
circulation patterns of oceans and the atmosphere cause regional sea-level variations. On time scales of decades these
changes have a larger influence on the sea level around New Zealand than global warming induced sea-level rise.
In the long term, rising seas are expected to increase the ero-sion of vulnerable beaches and cause more frequent
breaches of coastal protection structures. Quantitative predictions depend heavily on local variables, and only limited
long-term data of sufficient quality exist. Hence no national-scale as-sessment of coastal risks under climate change is
The agricultural sector has opportunities for productivity gains and diversification under climate change, but also
The key benefit to agriculture is likely to be from elevated carbon dioxide concentrations which could lead to
substan-tial improvement in growth rates and water-use efficiency. In addition, warmer conditions and lengthened growing
seasons could allow the long-term southward shift of climate-limited activities, and new crops and related industries
could be in-troduced. Currently resource-poor areas could benefit from such shifts.
The most significant risks are associated with the potential increase of droughts and floods and water limitations in
some areas, particularly in the east of New Zealand. Warmer temperatures could also make the growing of some current
fruit crops in some northern areas uneco-nomical. Shifting land-use activities to adapt to altered climate conditions
will incur costs, resulting in regional win-ners and losers. Pests and diseases could spread in range and severity, and
pasture composition is likely to change with uncertain outcomes to animal productivity and nutrient bal-ances. The full
range of effects has not been quantified yet.
The assessment of climate change impacts on agriculture has been greatly helped by the development of an integrated
as-sessment programme (CLIMPACTS) which combines climate and agricultural expertise. However, information on regional
climate change and its impacts is still too limited to quantify the overall economic effect on the agricultural sec-tor.
Adaptation to altered climate conditions would also influence future economic outcome through early implementation of
opportunities and mitigation of negative impacts. Overseas markets will also change under a warming climate, offering
indirect market risks and opportunities to New Zealand farmers.
With few exceptions, climate change alone is unlikely to be the dominant cause of native species extinction, but may act
as compounding pressure on ecosystems which are already under threat. Fragmented native forests of drier lowland
en-vironments in Northland, Waikato, Manawatu, and in the east from East Cape to Southland are probably the most
vul-nerable to climate change, and some terrestrial and freshwater species which are currently at their climatic limit
may be at long-term risk of extinction. However many com-plex interactions between elements of natural ecosystems,
introduced exotic species and climate are not yet fully incor-porated in assessment models.
Urban environment, transport and energy
The main threat to the urban environment comes from possi-ble increases in heavy rainfall which would put pressure on
drainage and stormwater systems and increase the risk of flooding in some areas. Erosion could also increase road
maintenance costs, but warmer winters would lead to re-duced costs for snow and ice clearing. Warmer conditions will
substantially reduce home heating costs, leading to re-duced electricity demand during the peak winter season, but
possibly increase demand for air conditioning during sum-mer. The reduced winter demand would combine with an increased
availability of water in hydroelectric storage lakes from projected rainfall increases over the Main Divide, pro-viding
the opportunity for a more balanced electricity supply and demand.
Higher temperatures are expected to reduce winter illnesses, but have also been found to be correlated with increased
mortality during summer. A warmer climate would also al-low the better establishment and spread of mosquitoes capable of
transmitting diseases such as Ross River virus and dengue fever. The impacts of climate change on human health are
however not just determined by climatic condi-tions, but also the vulnerability of the exposed population. Border
controls, vector eradication programmes, safe food and water supply, and primary health care services all influ-ence the
impact of climate change on actual changes in disease risks and outbreaks.
Recent research also found that climate change could lead to a delay in the recovery of the ozone layer. Ozone is
de-stroyed by chlorofluorocarbons (CFCs) used in refrigeration and as propellants. Since the banning of CFCs the ozone
layer was expected to recover over the next few decades, but scientists have found that emissions of other greenhouse
gases such as carbon dioxide and methane could delay this recovery by another 15 to 20 years. This would increase the
period during which New Zealanders are exposed to high levels of ultraviolet radiation, which is known to lead to skin
cancers. However quantitative model studies of the possible effects of greenhouse gases on the ozone layer are still
Climate impacts on Mâori
The reliance of Mâori on the environment as both a spiritual and economic resource makes them more vulnerable and less
adaptable to climate change. Land presently owned by Mâori is often of lower quality which makes it more prone to
invasion by subtropical grasses and erosion. Because of the high spiritual and cultural value placed on Mâori
traditional lands and statutory sales restrictions, business relocation in response to climate change may not be seen as
an adaptation option. Multiple land-ownership and generally lower socio-economic status could hinder implementation of
costly or non-traditional adaptation measures. This may increase the risk of reduced economic output from Mâori land
compared to the New Zealand agri-cultural sector as a whole. Impacts on the coastal environment are also of great
importance to Mâori culture and economy, but the impact of climate change on fisheries production is highly uncertain at
New Zealand has close social and institutional links with many Pacific Island countries. Many of these countries are
highly vulnerable to climate change from rising sea-level, changes in rainfall patterns affecting agricultural
productiv-ity, destruction of coral reefs, and human health effects of higher temperatures and vector-borne diseases.
Such impacts could have considerable flow-on effects for New Zealand through increased demand for development aid and,
in worst cases, disaster relief. Climate change in competing export countries will contribute to changing commodity
prices and market structures in some key export markets. These changes offer both risks and opportunities to New Zealand
exports, but information is too limited at present to allow predictions or outline specific adaptation strategies.
Summary and outlook
New Zealand’s climate is very likely to change during the 21st century. Impact projections are limited by uncertainties
of regional climate changes and frequency of extreme events. At this stage, an assessment of the overall impact of
climate change on New Zealand society and economy is impossible, but it is likely that there will be short-term winners
and los-ers. Negative impacts could be reduced and potential gains increased by ongoing proactive adaptation to altering
cli-mate conditions. Because of the regionally varying impacts of climate change and the different effects on different
sec-tors, future comprehensive quantitative impact studies and development of adaptation strategies would require
greater incorporation of climate effects in sector-specific models.