Temperature

This section describes changes in New Zealand's temperatures over time, and who might be most at risk of health impacts from temperature extremes.

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New Zealand’s climate is warming

Over the period 1909-2017 (Figure 1), the mean annual temperature in New Zealand rose at a rate of almost 1°C per 100 years [1]. Climate scientists predict that relative to 1986-2005, New Zealand will continue to warm by 0.7°C and 1.0°C by the year 2040 and 0.7°C and 3.0°C by the year 2090. Northern and eastern New Zealand will have the strongest warming trend [2].

Figure 1: Mean annual temperature anomaly in New Zealand, 1909-2017

NIWA

Source: NIWA (‘Seven-station’ temperature series), modified

Note/s: Red bars show a positive difference and blue bars show a negative difference from the 1981-2010 average temperature. The black line shows the linear trend over 1909 to 2017

Hot days are more common in northern and eastern New Zealand

There will very likely be an increase in the number of hot days (maximum temperatures above 25°C), particularly in the north of the North Island. At the same time, there will very likely be a decrease in the number of cold days (minimum temperatures below 0°C), particularly in the South Island [2].

Data from 2015-17 show hot days are more common in the north and east of both islands, whereas cold days are most frequent in parts of the South Island. Movie 1 and movie 2 show where these temperature extremes occurred over the past 18 years.  

Movie 1: Number of days over 25°C, 2000-2017 (three-year moving average), by Territorial Authority (TA)

 hotdays 032019

Movie 2: Number of days below 0°C, 2000-2017 (three-year moving average), by Territorial Authority (TA)

 colddays 032019

Note: For more information about the methodology, please download the metadata sheet and the factsheet.

A warmer climate will affect our health

Fewer cold days will result in fewer cold-related deaths and hospitalisations from cardiorespiratory (heart and lung) conditions [3].

Increased temperatures can affect health in several ways.

  • Gastrointestinal infections: The rate of gastrointestinal infections is affected by temperature. Research suggests that periods of higher temperatures are linked to an increase in salmonellosis notifications [4].
  • Infectious diseases: Increasing temperatures can change the geographical distribution of some mosquitoes, carrying infectious diseases.
  • Respiratory problems: Increasing temperatures bring a longer pollen season and increased fire risk, associated with increases in respiratory problems.
  • Cardiac (heart) problems: Heat is linked to worsening of heart problems and to an increase in overall death rates [3][5], and [6].
  • Heat stroke: Extreme temperatures can cause heat stroke. Young children, older adults, those with a chronic disease, and people working outdoors are especially at risk.

Effects on vulnerable populations

Populations that are more vulnerable to temperature-related health effects are: 

Combining temperature (Movie 1) and population data (see Population Vulnerability for more information) shows that Northland, the east coast of the North Island, and parts of the Bay of Plenty are likely to be regions where people will be particularly affected by the health effects of temperature increases. For example, many Māori live in the north and east of New Zealand, where hot days are projected to increase [2]. There are also high numbers of older people over 85 years living in northern and eastern areas such as Christchurch city, Auckland city, Whangarei and Hastings.

Information about the data

Specific change over time corresponding with climate change cannot be shown as the common baseline period in climate change science is 1960-1990, for which comparable data is not available.

Number of days above 25°C

Source: CliFlo. NIWA's National Climate Database

Definition: Climate station data of the daily maximum temperatures from around New Zealand was sourced from NIWA. One climate station was used per Territorial Authority (TA), except for Auckland City TA for which data from three weather stations were averaged. The number of days over 25°C per year for each TA has been averaged over the three-year time period. 

Number of days below 0°C

Source: CliFlo. NIWA's National Climate Database

Definition: Climate station data of the daily minimum temperatures from around New Zealand was sourced from NIWA. One climate station was used per Territorial Authority (TA), except for Auckland City TA for which data from three weather stations were averaged. The number of days over 0°C per year for each TA has been averaged over the three-year time period.

References

  1. NIWA. nd. ‘Seven-station’ series temperature data. URL: https://www.niwa.co.nz/our-science/climate/information-and-resources/nz-temp-record/seven-station-series-temperature-data (accessed 20 November 2018).
  2. Ministry for the Environment. 2016. Climate change projections for New Zealand: Atmospheric projections based on simulations undertaken for the IPCC 5th Assessment. Wellington: Ministry for the Environment.
  3. Smith KR, Woodward A, Campbell-Lendrum D, et al. 2014. Human Health: Impacts, Adaptation, and Co-Benefits. In: Barros VR,  Field C, Dokken D, et al (eds). Climate Change 2014: Impacts, Adaptation, and Vulnerability Part B: Regional Aspects Contribution of Working Group II to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (pp. 709-754). Cambridge, United Kingdom and New York, NY, USA: Cambridge University Press.
  4. Britton E, Hales S, Venugopal K, et al. 2010. Positive association between ambient temperature and salmonellosis notifications in New Zealand. Australian and New Zealand Journal of Public Health 34(2): 126-9. DOI: 10.1111/j.1753-6405.2010.00495.x (accessed 23 October 2018).
  5. Hales S, Salmond C, Town GI, et al. 2007. Daily mortality in relation to weather and air pollution in Christchurch, New Zealand. Australian and New Zealand Journal of Public Health 24(1): 89-91. DOI: 10.1111/j.1467-842X.2000.tb00731.x (accessed 23 October 2018).
  6. McMichael AJ, Woodruff R, Whetton P, et al. 2003. Human health and climate change in Oceania: A risk assessment. Canberra: Commonwealth of Australia.