This section sets out the state of our atmosphere and climate. It presents information on greenhouse gases, ozone and ultraviolet intensity, temperature, rainfall, and extreme weather.
Greenhouse gases, ozone, and ultraviolet intensity
This section presents information on greenhouse gases, ozone concentrations, and ultraviolet (UV) intensity in our atmosphere.
Greenhouse gases are increasing
Greenhouse gases in the atmosphere absorb heat radiating from the Earth’s surface causing warmer temperatures. The main greenhouse gases generated by human activities are carbon dioxide, methane, nitrous oxide, and carbon monoxide. Concentrations of these gases are measured by NIWA at Baring Head near Wellington. Carbon dioxide has the greatest impact over the long term because it persists in the atmosphere longer than the other greenhouse gases. However, the other greenhouse gases have a significant impact in the short term, because they absorb much more heat per kilogram than carbon dioxide.
Carbon dioxide concentrations measured over New Zealand increased 21 percent since measurements began in 1972 (see figure 15). This is an increase of about 1.6 parts per million a year (0.5 percent).
Note: Baring Head is near Wellington. It is a site that is less likely to be influenced by local sources of pollution. These observations are made only when the wind is blowing from the south and away from any likely local sources of gas emissions. This gives a measure representative of the concentrations over the Southern Ocean. Data are unavailable for some periods.
This graph shows the carbon dioxide concentrations at Baring Head between 1972 and 2013. Visit the MfE data service for the full breakdown of the data.
Methane and nitrous oxide concentrations also increased significantly since they were first measured in 1989 and 1996, respectively. On the other hand, carbon monoxide concentrations decreased significantly since first measured in 2000. Globally, technological improvements and stricter controls on vehicle and industrial emissions are leading to lower emissions of carbon monoxide (Mikaloff-Fletcher & Nichol, 2014).
The measurements taken in New Zealand are consistent with other observations around the globe. This is expected, because these gases get mixed around the globe by weather systems (Mikaloff-Fletcher & Nichol, 2014).
For more detail see Environmental indicators Te taiao Aotearoa: Greenhouse gas concentrations.
Ozone concentrations over New Zealand are comparable to countries of similar latitudes
The thickness of the ozone layer is significant because ozone absorbs UV light from the sun and acts as a filter against sunburn and other damage (eg to plastic and fabric). Changes in ozone concentrations can also influence the risk of skin cancer.
The amount of ozone in an atmospheric column is measured in Dobson units, where 1 Dobson unit corresponds to the amount of ozone required to form a 0.01 millimetre layer of pure ozone. The global average ozone is 300 Dobson units (Liley & McKenzie, 2007), slightly lower than the average ozone over New Zealand (307 Dobson units). Over New Zealand, the ozone layer ranges from about 275 Dobson units in autumn to 345 Dobson units in spring (see figure 16). Ozone varies by around 15 Dobson units from day to day (around 5 percent). Ozone concentrations over New Zealand are similar to other places around the world at similar latitudes.
Note: Maximum, minimum, and average ozone concentrations are shown.
This graph shows the daily maximum, average, and minimum column ozone by the day of the year over the period 1979 to 2013. Visit the MfE data service for the full breakdown of the data.
A small but discernible downward trend is evident in ozone concentrations over New Zealand. However, this may only have had a small impact on our UV levels.
For more detail see Environmental indicators Te taiao Aotearoa: Ozone concentrations.
The ozone hole only affects New Zealand’s ozone and UV levels when it breaks up in spring – when it can send plumes of air with lower ozone concentrations over the country. Even then, the ozone above New Zealand drops only about 5 percent, which is within the normal daily variation.
For more detail see Environmental indicators Te taiao Aotearoa: Ozone hole.
New Zealand’s UV intensity is relatively high
Peak UV intensities in New Zealand are about 40 percent greater than at comparable latitudes in the Northern Hemisphere. The strength of UV light is measured using a solar UV index (UVI) or sun index. A UVI above 11 is extreme.
In New Zealand, UV indexes vary day to day, and showed no consistent trend across the five monitored sites between 1981 and 2014. In summer, the UVI often exceeds 11. For example, the northernmost site, Leigh, had an average of 73 days with a UVI greater than 11. In winter, the UVI can be as low as 1 even on clear days, mainly because the sun is low in the sky.
For more detail see Environmental indicators Te taiao Aotearoa: UV intensity.
Temperature, rainfall, and extreme weather
This section presents information on average temperatures, rainfall, and extreme weather. We also collect data on sunshine hours, but that is not discussed here (for information on sunshine hours see Environmental indicators Te taiao Aotearoa: Sunshine hours).
Average temperatures have risen
The average annual temperature in New Zealand increased by about 0.9 degrees Celsius over the last century (a statistically significant trend), slightly lower than the global average land-based temperature increase of around 1–1.2 degrees Celsius (NIWA, 2015) (see figure 17).
The Intergovernmental Panel on Climate Change concluded that global warming is beyond doubt, and it is extremely likely that human-caused pressures such as the burning of fossil fuels has been the primary cause since 1950 (IPCC, 2013).
Note: Data from seven sites around the country, adjusted for changes in site location. The plot shows the difference from the 1981–2010 average (known as ‘normal’). Climatologists use the term ‘normal’ to refer to an average of the weather across a 30-year period.
This graph shows the national average temperature as the difference from 'normal' between 1909 and 2013. Visit the MfE data service for the full breakdown of the data.
New Zealand’s average temperature, as estimated from seven monitored sites, fluctuates by about 0.4 degrees Celsius from year to year. This is a natural variation not directly linked to human-caused pressures. These year-to-year changes can be linked in part to climate oscillations such as the El Niño Southern Oscillation.
The increase in temperature is also reflected in ‘growing degree days’. Growing degree days is the total days over a year in which the mean daily temperature is higher than a base value (10 degrees Celsius).
Of the 29 sites assessed, 18 showed upward trends, with a median increase across all sites of 0.22 growing degree days per year.
Rainfall is highly variable with no clear trend
Rainfall is highly variable both geographically and from year to year, so we have been unable to determine any long-term trends. However, it is expected that climate change will influence rainfall (and other forms of precipitation) over the longer term.
Geographically, annual average rainfall varies from less than 500 millimetres in dry years in places like Central Otago, to over 4,000 millimetres in mountainous areas such as the Tararua Range, and even more in the Southern Alps (see figure 18).
For more detail see Environmental indicators Te taiao Aotearoa: Annual rainfall.
This map illustrates the average annual rainfall across New Zealand between 1972 and 2013. Visit the MfE data service for the full breakdown of the data.
Fewer days with gale-force winds but no clear trends in other extreme weather
This section presents information about three common elements of severe weather events: annual three-day rainfall maximums, the number of days with wind gusts above gale force, and lightning frequency.
Three-day rainfall data capture rainfall events likely to cause widespread flooding in affected areas. These data show the greatest rainfall total over any three-day period for each year, at each site. The data vary from year to year, so we cannot identify any statistically significant trends. While these data (see figure 19) show the maximum three-day rain totals for each year, they do not show the frequency of heavy rainfall events in a year.
Note: Data was unavailable for Wellington in 1993.
This graph shows the annual maximum three-day rain totals for Christchurch, Wellington, and Auckland, between 1950 and 2013. Visit the MfE data service for the full breakdown of the data.
We estimate damaging wind by the number of days a year wind gusts exceed gale force (61 kilometres an hour). The data show that Auckland, Wellington, and Christchurch regularly experience gale-force gusts, but Wellington is particularly prone to gale-force winds. Since 1975, the occurrence of potentially damaging wind has decreased in Wellington. Monthly (but incomplete) data for Christchurch and Auckland also suggest a smaller decrease (see figure 20). It is not clear whether this decrease is part of a natural cycle or is influenced by climate change. Studies predict global climate change may increase the frequency of damaging wind events in winter in almost all areas in New Zealand, and decrease the frequency in summer (Mullan et al, 2011).
Note: Two of the three selected sites have missing data for some years. Gusts above gale force – above 33 knots, approximately 61 km/h.
This graph shows the number of days with wind gusts above gale force in Wellington, Auckland, and Christchurch, between 1975 and 2013. Visit the MfE data service for the full breakdown of the data.
Annually, there are about 190,000 lightning strikes on the New Zealand land mass and over coastal seas. This is not frequent by international standards. Lightning strikes are most frequent on the West Coast of the South Island. The data show a high degree of variability over the 14-year period from September 2000 to December 2014. However, thunderstorms, and therefore lightning, are expected to increase in frequency and intensity as a result of climate change (Mullan et al, 2011).