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Impacts: Aotearoa’s changing climate

New Zealand’s changing climate

(Image: Marcus Kauffman)

Aotearoa’s changing climate


“This century, climate change will alter New Zealand’s natural water cycle significantly. It will change how much rain and snow we receive, and at what time of year. It will change how much water is stored in the soil, snow, glaciers and aquifers. It will change how much water evaporates back to the atmosphere and how much flows through streams and rivers to the coast. And it will change the severity of droughts, floods and power shortages.”  Deep South

You had this drought that went on and on, and then about ten years’ worth of water in a single morning.”Minister for Climate Change, James Shaw after the July 2020 flooding in the Far North

Fig. 1: Instructions for this interactive graph (Credit: The Institute.)

  • Mouse over anywhere on the graph to see the changes in global temperatures over the last thousand years.
  • To see time periods of your choice, hold your mouse button down on one section then drag the mouse across a few years, then release it.
  • To see how this compares to the past 771,000 years, click on the ‘time’ icon on the top left.
  • To return the graph to its original position, double-click the time icon.

Why the Earth’s climate is changing

Video 1 explains how greenhouse gasses work. The atmosphere can hold ~7% more moisture for every 1°C warming, and the atmosphere already is more than 1°C warmer than it was in 1850.

Video 1: How greenhouse gasses work to maintain or change the climate.
Fig. 2: Based on IPCC AR4 for the period 1993-2013. (Image: Skeptical Science).

Climate outlook for Aotearoa: marine heatwaves

The oceans cover 70% of Earth and the deepest areas are almost 4,000m; that’s a huge area to store heat. Additionally the ocean is dark, so it has a very low albedo meaning that it can absorb much more heat than the land. New Zealand’s weather is strongly influenced by the temperature of the ocean (Fig. 3). Warming is also affecting oceanic currents including ENSO (El Niño and La Niña) and the Antarctic Circumpolar Current. These play a significant role in New Zealand and the world’s climate. (About 63% of the extra heat is in the upper ocean and 30% from 700m down to the ocean floor). This extra heat is also affecting the life in the oceans from ocean acidification and heat stress leading to events like coral bleaching.

Recent research reveals that the oceans are heating 40% faster than the IPCC 2013 Fifth Assessment Report (AR5). We already are seeing and feeling the effects:

“During austral [southern hemisphere] summer 2017/18, the New Zealand region experienced an unprecedented coupled ocean-atmosphere heatwave, covering an area of 4 million km2. Regional average air temperature anomalies over land were +2.2 °C, and sea surface temperature anomalies reached +3.7 °C in the eastern Tasman Sea… The event persisted for the entire austral summer resulting in a 3.8 ± 0.6 km3 loss of glacier ice in the Southern Alps (the largest annual loss in records back to 1962)… The best match suggests this extreme summer may be typical of average New Zealand summer climate for 2081–2100, under the RCP4.5 or RCP6.0 scenario.”  Salinger et al 2019

Rather than a glimpse into what summers might be like after 2081, similar warming over the ocean happened again in 2018/2019 (Fig. 3).

Fig. 3: Changes in ocean temperatures around New Zealand 2010 – 2019 (Image: NIWA). Warmer oceans means there’s more water vapour over the water. And warmer air can carry more moisture. This powers tropical cyclones, so they may reach New Zealand more often, bringing greater risks of destructive winds and flooding.

Then in the summer of 2019/2020 something extraordinary happened:

“In an event that is unprecedented in 40 years of record-keeping, temperatures over Antarctica rose rapidly, causing the polar vortex over the Southern Hemisphere to break down and even reverse direction. This had cascading effects on weather patterns.”Andrew Freedman, January, 2020

Wobbly weather patterns: the polar vortex

Polar regions are warming more than twice as fast as the rest of the planet, and this is changing our weather, which is strongly influenced by jetstreams including the polar vortex (Video 2). Extreme hot or cold weather is often ‘stuck’ over one place for long periods.

Video 2: Short introduction to how Earth’s weather works

As we saw in 2019/2020, ‘cascading effects‘ across the Tasman also had an impact on New Zealand in unexpected ways: soot from catastrophic forest fires that covered our glaciers reduced their albedo. This causes them to melt faster, accelerating positive (warming) climate feedback effects.

The marine heatwave returned again in 2020 (Fig. 4).

Fig. 4: 2020 Marine Heatwave (image: WeatherWatch).

Climate outlook for Aotearoa: extreme weather

The following is from the Ministry for the Environment: First national climate change risk assessment for New Zealand (NCCA) August 2020, page 8:

“New Zealand’s climate is warming, sea levels are rising, and extreme weather events are becoming more frequent and severe.The National Institute of Water and Atmospheric Research(NIWA) developed the climate change projections used for this risk assessment after the release of the IPCC Fifth Assessment Report. They include the following trends:

  • In the last 100 years,our climate has warmed by 1°C. If global emissions remain high, temperatures will increase by a further 1.0°C by 2040 and 3.0°C by 2090.
  • In the last 60 years, sea levels have risen by 2.44 mm per year. If global emissions remain high, sea levels will increase by a further 0.21m by 2040 and 0.67m by 2090.
  • Extreme weather events such as storms, heatwaves and heavy rainfall are likely to be more frequent and intense. Large increases in extreme rainfall are expected everywhere in the country, particularly in Northland due to a projected increase in ex-tropical cyclones.
  • The number of frost and snow days are projected to decrease, and dry days to increase for much of the North Islandand for some parts of the South Island.
  • Drought is predicted toincrease in frequency and severity, particularly along the eastern side of the Southern Alps.
  • Increased northeasterlyairflows are projected in summer and stronger westerlies in winter, the latter particularly in the south of the South Island.
  • Wildfire risk is predicted to increase in many areas towards the end of the century, due to higher temperatures and wind speeds, and decreased rainfall and relative humidity.”

Predicting the future

“We tend to have this idea that our climate is gradually warming and these types of impacts will be gradual…but the Earth system doesn’t work like that. There’s no reason to expect that a gradual increase in temperature will contribute to a gradual increase in the types of fires we’re having to fight.”Professor Nerilie Abram, ANU

As the climate warms, the weather system in the Indian Ocean, the Indian Dipole (the Pacific ‘sister’ of El Niño/La Niña) is expected see more strong “positive” events similar to the 2019-20 Australian drought and bushfires that dumped ash on our glaciers, hastening their melting.

The current climate change projections for Canterbury are based on the 2013 IPCC  Assessment Report.  As real-world events and the latest research and satellite date show we have outpaced several of these climate projections, the National climate change risk assessment for New Zealand report uses the RCP8.5 (worst case scenario). It also states that:

“More extreme scenarios are possible, and the sensitivity of the climate system remains uncertain.”

Improved earth systems climate modelling is now underway that will help inform the IPCC Sixth Assessment Report due in 2022.

Individuals, whanau, communities, and businesses across all sectors should not delay adaptation planning and risk mitigation until new climate models for New Zealand are released in 2022, as managing weather- and climate-related risks will need to be continuously re-evaluated and adapted given that climate tipping points are being passed.

The risk of vulnerable areas and buildings (including critical infrastructure) becoming uninsurable, is increasing. Protecting and restoring ecosystems is a cost-effective and proven strategy for managing these risks.


Climate vs weather:

Climate is an average of weather conditions over time, generally 30 years. Climate is affected by landmasses such as mountains and deserts, the amount and type of vegetation, and the oceans, all of which in turn affect climate. Climate changes with latitude. The north of the North Island is closer to the equator, so it gets more sunlight throughout the year and warmer temperatures and is more likely to feel the impacts of tropical cyclones. Stewart Island Rakiura is much further south, so it has shorter days, a cooler climate, and is often affected by weather systems originating closer to Antarctica.

Weather is what we experience over short time frames (minutes to weeks) due to atmospheric conditions. For example, an ‘average annual rainfall of 1m/year’ may fall as 80cm in one catastrophic event, while the rest of the year suffers near-drought conditions.

Not everywhere is warming at the same pace. The Arctic and Antarctic are warming much faster than the tropics due, an effect known as ‘polar amplification‘. This affects New Zealand because our weather systems are influenced by oceanic currents as well as atmospheric conditions, and because of our proximity to Antarctica.

Net emissions:

Net emissions means gross greenhouse gas emissions from all industrial activities, burning fossil fuels for energy, and agriculture, minus carbon sinks from forestry, changing agricultural to improve soils, and regenerating natural ecosystems. However, instead of declining, global emissions continue to increase each year. Covid-19 has meant a temporary respite due to reduced transport, however that has not changed emissions from agriculture and manufacturing in China has resurged. Moreover, dangerous tipping points are being breached, which means natural carbon sinks are now becoming sources of methane and carbon dioxide.

Representative Concentration Pathways (RCPs):

The represent the concentration of greenhouse gasses in the atmosphere based on how these gasses retain heat.

  • Heat is measured in watts per metre squared, written as W⋅m2
  • In most graphs and models, the numbers 2.6, 4.5, 6.0, and 8.5 are W⋅m2 . However, ‘W⋅m2‘ is implied, and the four units are written instead as four scenarios that will likely result if that much heat is in the atmosphere: RCP2.6 being the lowest amount of heat and RCP8.5 being the most. Hence, the ‘RCP8.5’ scenario is the ‘worst case’ scenario.
  • These scenarios are based on models for the 2013 IPCC Fifth Assessment Report. They were developed in the years leading up to this report, so the data is at least 7 years old. Limitations and shortcomings are outlined here (this website).
  • In some graphs and reports (not on this page), the numbers are written without a decimal place: RCP26, RCP85 etc.

References and further reading