This section reports on the impacts of a changing climate. The modest number of impact measures in this section is in part due to the difficulty of attributing long-term climate change to changes in natural and human systems that are typically variable and complex.
We use our own data to report on ocean warming and acidification, sea-level rise, glaciers, soil moisture and drought, and the occurrence of food- and water-borne diseases and influenza. We also draw from New Zealand-based research to discuss three case studies on the impacts on New Zealand’s biodiversity associated with temperature increases.
Our marine environment 2016 discusses in depth the effects of our changing climate on our oceans. The main points are summarised below.
The pH of the ocean off the Otago coast has decreased 0.03 units (meaning increased acidity) since 1998.
Globally, the oceans are increasing in acidity as they absorb some of the additional carbon dioxide in the atmosphere emitted by human activities. The longest record we have for measuring the acidity of New Zealand’s oceans is for the subantarctic ocean off the Otago coast. The record shows that the pH of the east subantarctic ocean has decreased 0.03 units (meaning increased acidity) since 1998. We expect more data from more locations to be available in the future.
The rate of decrease (0.0015 units per year) is consistent with global trends (Bates et al, 2014). Globally, the average pH of ocean surface waters has decreased by about 0.1 units since the beginning of the industrial era (IPCC, 2013). While this decrease may seem small, the pH scale is logarithmic – so a decrease in pH by 0.1 units is equivalent to a 26 percent increase in acidity (IPCC, 2013).
The impacts of this acidification are still being investigated. However, it could cause widespread changes, and marine experts rank it as the most serious threat to our marine habitats (MacDiarmid et al, 2012). See also Our marine environment 2016.
New Zealand’s annual average sea-surface temperatures measured by satellite have not shown a trend over the past 20 years.
Sea-surface temperatures fluctuate naturally with the seasons and across decades. Over the last century, our sea-surface temperature has increased 0.71 degrees Celsius (Mullan et al, 2010), matching worldwide increases (Hartmann et al, 2013). However, recent satellite data, only available since 1993, show no trend in sea-surface temperature change in the Tasman Sea and New Zealand’s oceanic, subtropical, and subantarctic waters. This result is not surprising given the short time these data have been available and the year-to-year temperature variations. See also Our marine environment 2016.
Ocean acidification and warming may cause widespread harm to marine ecosystems, for example, by reducing the survival and growth rates of marine species, extending or reducing the range of species, and modifying habitats. The impacts could occur across New Zealand’s entire ocean area, with implications for biodiversity, marine-based industries such as commercial fishing and aquaculture, and Māori customary practice (see Our marine environment 2016).
The marine environment is particularly important to the Māori economy (including fishing operations, incomes, and ocean-based investment). As at 2015, kaimoana (fish, crustaceans, such as crayfish and shrimp, and molluscs, such as shellfish) was the top export commodity of Māori authorities (Statistics NZ, 2016).
Sea level has been rising around the globe as a result of the world’s oceans expanding as they warm and because ice previously stored in glaciers and in parts of the polar ice sheets has been melting. Globally, sea level rose 19 centimetres between 1901 and 2010 (IPCC, 2014a).
However, sea-level change is not uniform around the world. This is because of the rising and sinking of land relative to sea, regional variations in ocean temperatures and circulation, and the adjustment of Earth’s gravitational field to the changing ice sheets. For the same reasons, sea-level rise is not consistent around New Zealand’s coastline.
Since 1916, our coastal sea level has risen up to 22 centimetres at monitoring sites around the country.
Our coastal sea level is rising, with increases of up to 22 centimetres since 1916 (depending on local land motion), recorded at monitoring sites around the country. Over this period, sea level rose an average of 1.8 millimetres a year across monitoring sites. This agrees with the global record from tide gauges of about 1.7 millimetres a year between 1901 and 2010.
In the satellite era (since 1993), global mean sea level has risen about 3.4 millimetres per year (University of Colarado, nd). It is likely that similarly high rates occurred between 1920 and 1950. Satellite measurements have the significant advantage of near-global coverage and are not affected by local land movements. Since 1993, data from satellites and tide gauges has been in agreement. Globally, average sea levels will continue to rise at a faster rate in the 21st century (IPCC, 2014a). See also Our marine environment 2016.
Sea-level rise is a long-term threat that will have an increasing effect on the coastal marine zone. Rising sea levels and more intense heavy rainfall events associated with climate change are projected to increase coastal flooding and erosion, which may in turn cause damage to coastal ecosystems, housing, and critical infrastructure, such as roading, sewage, and power supply (Reisinger et al, 2014).
Globally, the sea level is projected to rise by about 20 to 40 centimetres by 2060 (relative to 1986–2005) (IPCC, 2013). While New Zealand’s sea-level rise has aligned with the global average so far, at least one study projected that our sea-level may rise a little faster than the global average in the future (Ackerley et al, 2013). Moreover, with rising seas, we can expect tides, waves, and storm surges (commonly known as extremely long, slow waves) to reach further inland more regularly, resulting in more frequent and serious flooding (PCE, 2015).
For Māori, sea-level rise poses threats to a mix of interests, assets, and values (King et al, 2010; Manning et al, 2015). Many Māori communities have ancestral ties with coastal areas, and relationships are maintained (often at a distance) with cultural heritage (eg marae and burial grounds) and food-gathering sites. These interests and activities are deeply connected with identity and well-being. Some communities face hard decisions about how long they can remain living near coastal areas prone to erosion, storm surges, and peak tides associated with sea-level rise.
There is an increasing recognition and concern about the impacts of coastal erosion and sea-level rise on cultural sites, including early settlement sites and burial grounds (McFadgen, 2007). As sites are lost to erosion or the encroaching sea, we lose the knowledge they offer about early Māori and European settlement.
A 2013 study of the impact of climate change on the archaeology of the coastline in the Whangarei district suggested increases in the likelihood and severity of detrimental impacts on archaeological sites, one-third of which were already threatened by other pressures. Middens (piles of pre-historic or historic domestic refuse, such as discarded shells or animals bones, particularly around a cooking area) and small sites of early Māori occupation are particularly at risk (Bickler et al, 2013).
Extreme coastal flooding, usually due to storm surges coinciding with very high tides, already causes disruption and damage in some places around New Zealand’s coastline. As sea levels continue to rise, local councils will almost certainly face difficult decisions around what investments to make towards protecting land and existing structures versus retreating from some areas and helping communities adapt. Some local councils are already planning and adapting to new conditions (see box 5).
Box 5 The implications of sea-level rise for South Dunedin
South Dunedin lies on a spread of low-lying flats between Otago Harbour and the Pacific Ocean. The urban area is generally based on land reclaimed from coastal dunes and marshlands in the 1880s. As a result, the groundwater table lies close to the surface and has many direct underground connections to the Pacific Ocean and Otago Harbour.
In 2015, nearly 2,700 homes, 116 businesses, and 35 kilometres of roads lay less than 50 centimetres above the spring high-tide mark, with more than 70 percent of homes lying lower than 25 centimetres elevation (PCE, 2015).
The global projections of the sea level rising by 20 to 40 centimetres by 2060 (IPCC, 2014a) mean South Dunedin's water table will rise, which is likely to increase surface ponding and flooding after heavy rain. Such flooding can damage roads, pipes, cables, buildings (which will also experience ongoing dampness), and parks and other recreational facilities. The projected sea-level rise could cause extreme high-water events to occur every two years at Port Otago (PCE, 2015).
In June 2015, prolonged heavy rain caused extensive flooding when drainage systems were overwhelmed. Numerous roads and properties were damaged. The Dunedin City Council had already commissioned an assessment of options for protecting South Dunedin in the case of sea-level rise. Options range from building an underground sea wall to prevent seawater pushing up groundwater to pumping water away from the ground to sinking 'dewatering wells' along the coast to absorb excess water. At the same time, the Council is investigating the viability of a managed retreat (PCE, 2015).
Flooding in South Dunedin in June 2015. (Photo: Otago Daily Times)
Our glacier ice volume decreased 25 percent from 1977 to 2016.
New Zealand’s mountains are home to 3,144 large glaciers (each covering more than 1 hectare). Most of these glaciers are located along the Southern Alps of the South Island. However, there are also 18 on the flanks of Mount Ruapehu in the North Island (Chinn, 2001).
Glacier ice volume is strongly influenced by temperature and precipitation. Changes to ice accumulation and melting can affect ecological and hydropower resources downstream, as well as important cultural values and tourism.
Over the past 20 years, almost all the world’s glaciers have been shrinking (IPCC, 2013). New Zealand’s glacier ice volume decreased 25 percent from 1977 to 2016 (see figure 13). This equates to a loss of 13.3 cubic kilometres of ice.
Note: A glacial ice year runs from 1 April to 31 March.
This graph shows New Zealand’s annual glacial ice volume, 1977–2016. Visit the MfE data service for the full breakdown of the data.
New Zealand’s longest glacier, the Tasman, has retreated roughly 5 kilometres since 1980. While this means the glacier is more difficult to climb, it has presented a different tourism opportunity. Guided boat trips are now held on lakes that have formed over the last 30 years (Ministry for the Environment, 2017b).
The West Coast’s Fox and Franz Josef glaciers have each retreated about 3 kilometres since 1940, and in 2012 and 2014 respectively, they became too dangerous for tourists to be guided onto them. This marked the end of almost a century of glacier guiding from the valley floor (Anderson et al, 2016).
While climate warming will lead to loss of frozen water resources, the magnitude, timing, and distribution of changes in meltwater from New Zealand’s glaciers is unclear.
New Zealand’s native flora and fauna evolved in near isolation, forming our country into a biodiversity ‘hotspot’ that features many species found nowhere else on Earth. Despite humans only arriving in this country comparatively recently (circa 1250AD), our biodiversity has declined rapidly because of the cumulative effects of land disturbance, overexploitation of resources, and introduced pest plants and animals. A changing climate has the potential to exacerbate these existing pressures.
It is difficult to predict the specifics of the impact of a changing climate on our native flora and fauna. This is because biodiversity and supporting ecological systems are complex; one change to a system, however small, can have compounding effects. However, we do know that our biodiversity is already vulnerable to pests and diseases (see box 6). A warming atmosphere and ocean will affect the range, distribution, and success of pest and weed species, which are often more resilient to harsher environmental pressures. In addition, we know that the distribution or breeding success of some species is tied to climate (mainly temperature and rainfall), and those species will be affected by climate change.
Box 6 presents three examples of how climate change is already thought to be affecting three species resident in New Zealand.
We can expect to face possibly costly decisions around how we manage the effects of a changing climate for our unique and celebrated native biodiversity. This includes decisions about relocating vulnerable species whose ideal climatic conditions are expected to shrink.
North Brother Island tuatara. (Photo: Geoff Wilson)
Changes in climate could well affect native fauna and flora that are taonga (treasures) to Māori. This poses an additional challenge on Māori ability to exercise kaitiakitanga (environmental stewardship), a cultural value that is at the heart of their identity (Selby et al, 2010). The well-being of our natural systems is of paramount importance to whānau, hapū, iwi, and Māori business values.
Box 6 Biodiversity case studies: Impacts of increasing temperatures on tuatara, wasps, and seed production
Tuatara sex ratios
The sex of many reptiles, including our iconic tuatara, is determined by the temperature experienced during their embryonic development. Warmer temperatures in tuatara nests produce more male hatchlings and lead to decreased body condition in female tuatara, making them less viable for mating.
North Brother Island in the Cook Strait hosts a tuatara population where the male-to-female sex ratio has changed noticeably since field studies on the island began in 1988. Surveys from 1988 to 1998 reported a sex ratio of 1.66 males for every female. The most recent estimate (for surveys from 2005 to 2012) suggests there are now 2.36 males for every female (Grayson et al, 2014).
An estimated ratio of 5.7 males per female would make local extinction inevitable for this tuatara population. This ratio does not mean North Brother Island tuatara would immediately disappear. Because they live so long (up to 70 years in the wild), extinction may take a further 380 years (Grayson et al, 2014), meaning generations of New Zealanders would witness the population's decline with no chance to stop it.
Isolation and fragmentation can exacerbate the effects of climate change. North Brother Island is small (4 hectares) with only one type of environment for its tuatara population. Nearby Stephens Island is much larger (150 hectares) and offers a range of environments for its tuatara population. No change in tuatara sex ratios has been observed on Stephens Island to date.
Northwest South Island introduced wasp abundances
Insects play an important role in ecological processes such as pollination and decomposition. Their body temperatures are regulated by environmental temperatures, so they are particularly sensitive to climate changes.
The introduced common wasp is an invasive species in New Zealand that is particularly problematic in some beech forests because it consumes large quantities of honeydew, which is an important food source for native birds, bats, insects, and lizards. The wasps also eat huge numbers of native insects and have even been observed killing newly-hatched birds.
We have some of the highest common wasp densities in the world because of our mild winters and lack of predators. Warm, dry springs have been linked to increased wasp abundances in six beech forests near Nelson (Lester et al, 2017).
We cannot predict whether wasp abundances will continue to increase with the predicted increases in temperature. This is because a changing climate may lead to ecosystem changes (such as food supply shortages) that will limit their abundances.
The amount of seed produced by a plant can vary widely across years depending on multiple factors, including the climate. Mast seeding, the synchronised production of large seed crops, occurs irregularly – every four to five years (Barron et al, 2016).
Mast seeding creates an abundance of food that is vital for some of our native bird species' survival but also dramatically increases introduced predator numbers (eg mice, rats, and mustelids such as weasels, stoats, and ferrets).
Research on five native plants species (beech, hīnau, mountain daisy (Celmisia), snow tussock (Chionochloa flavescens), and flax) highlights that masting for these species is triggered by temperature variation. Specifically, an increase in temperature from one summer to the next stimulates the production of more seeds in the following summer (Kelly et al, 2013). Our understanding of this process allows us to predict large masting events and plan animal pest management strategies (see figure 14).
The year-to-year temperature difference trigger means masting events won't occur every year. Even though our temperatures are increasing over time, they do not increase in a straight line – some years will be cooler than the previous year. We still have a lot to learn about the potential impact of climate change on masting events, and it is an area that requires ongoing research.
This figure shows the relationship between beech tree seed drop, temperature, and pest population increases.
Soil moisture and drought
Most of New Zealand had drier than normal soils over the period 2013–16.
Soil moisture is vital for plant growth. When plants cannot access the water they need, growth is reduced, affecting crops and food for livestock and native biodiversity. A drought can have significant social and economic costs, particularly for rural communities.
From 1972 to 2016, our soils became drier at 7 of 30 sites. Soil moisture increased at only one site – Timaru. Over the three years from 2013 to 2016, most of New Zealand had drier than normal soils.
The frequency and intensity of drought in drought-prone regions are expected to increase as temperatures rise and rainfall patterns change (Ministry for the Environment, 2016).
The 2012–13 drought was one of the most extreme New Zealand had experienced in the previous 41 years and was unusual for being especially widespread, affecting the entire North Island and the west coast of the South Island. The worst effects were felt in the North Island (southern Northland, South Auckland, Waikato, Bay of Plenty and the central plateau, Wairarapa, Rangitikei, Ruapehu, Gisborne, and Hawke’s Bay), as well as parts of the north and west of the South Island (Ministry for Primary Industries, 2013).
The New Zealand Treasury estimated that reduced agricultural production alone from the 2012–13 drought would reduce GDP by about 0.7 percent or about $1.5 billion in 2013 (New Zealand Treasury, 2013). Research suggests that, while not causing the drought, human-induced climate change played an important role in its intensity (Harrington et al, 2014).
Drought in Wairarapa 2012–13. (Photo: NIWA)
Soil moisture and drought is one indicator of a range of potential future impacts for agriculture and other primary industries. Impacts are regionally and locally specific and may be both positive and negative. Alongside drought, for example, impacts may include: change in yield and quality of pasture, trees, broad-acre crops (such as wheat, barley, oats), and pasture species; changes in pressures from weeds, pests, and diseases; stress on animals and plants from increased warm days (above 25 degrees Celsius); and water shortages and increased irrigation demand (Clark et al, 2012).
The Māori economy is vulnerable to climate impacts as a large proportion of Māori authorities’ operations are directly or indirectly involved in natural resource management (Statistics NZ, 2016), for example, farming and forestry. In 2015, agriculture accounted for one in five Māori authority enterprises (Statistics NZ, 2016).
Occurrence of food- and water-borne diseases and influenza
Data from 2007 shows a clear link between warmer summer months and the incidence of some food-borne diseases.
The natural variability of New Zealand’s climate can influence the prevalence of diseases from year to year and season to season. In the longer term, the incidence of such diseases may increase or decrease as the climate warms and rainfall patterns change (Hambling, 2012; Tompkins et al, 2012; Lal et al, 2015).
We report on data for the incidences of disease caused by the bacteria Campylobacter and Salmonella and water-borne disease caused by the microscopic parasite Cryptosporidium. Data from 2007 to 2016 associate warmer summer months with higher incidences of Salmonellosis and Campylobacter, while incidences of Cryptosporidiosis peak in spring.
Data from 2000 correlate the year’s cooler months with higher incidences of influenza.
A warming climate may influence the prevalence of cold-related illness over the long term. We report on the occurrence of influenza. Data from 2000 to 2016 correlate the year’s cooler months with higher incidences of influenza.
We can expect to face a range of climate-related health risks as our climate continues to warm. Direct impacts of climate change may include increased exposure to heat waves, flooding, and fires. Indirect impacts may include exposure to increasing pollen levels and allergenicity (and therefore risk of allergies) and new diseases borne on carriers (such as mosquitos) whose ranges are influenced by climatic factors. Other indirect health risks stem from socio-economic and mental health stressors, for example, through climate-related migration, housing pressures, and reduced food security (Royal Society Te Āparangi, 2017).
A Māori world view of health incorporates the importance of the state and condition of the environment to identity, health, and well-being, recognising the deep kinship between humans and the natural world (Harmsworth & Awatere, 2013). Thus, climate change could affect Māori sense of well-being, for example, the anxiety and grief at being forced to leave ancestral homelands due to sea-level rise and losing access to traditional coastal food gathering sites.