New Zealand’s changing climate
(Image: Marcus Kauffman)
New Zealand’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
- Adding too many greenhouse gasses into the atmosphere has caused global warming; this is changing our climate (Video 1).
- The oceans have absorbed ~93% of global warming and are heating up 40% faster than the IPCC estimated in 2013.
- The atmosphere holds
~7% more water for every 1°C warming.
- Earth is >1°C warmer than it was 150 years ago (Fig. 1).
- Collectively, this means we already are experiencing climate change and with it, extreme weather events.
- Any drop in net emissions won’t reverse warming or return us to a ‘normal’ climate as there’s a long lag time between emitting greenhouse gasses and their effect (see the last time there was this much carbon dioxide in the atmosphere).
- This is increasingly costly for all of us in a multitude of ways, from extreme weather, floods (rain and/or rivers), rising sea levels, ocean acidification, and loss of critical ecosystem services we need to survive.
Fig. 1: Instructions for this interactive graph (Credit: The 2°
- 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
Climate outlook for NZ: 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.
“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).
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.
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).
Climate outlook for NZ: 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 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.
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 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⋅m−2
- In most graphs and models, the numbers 2.6, 4.5, 6.0, and 8.5 are W⋅m−2 . However, ‘W⋅m−2‘ 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
- NIWA: New Zealand’s climate
- NIWA: National Climate Centre
- NIWA: Climate change
- Ministry for the Environment: First national climate change risk assessment for New Zealand
- NIWA: Climate change for students
- NIWA: The impact of El Niño and La Niña on New Zealand’s climate
- Deep South Science Challenge (NZ): Will your property become uninsurable?
- Deep South Science Challenge (NZ): Planning for coastal adaptation
- Deep South Science Challenge (NZ): How should the risks be shared?
- Deep South Science Challenge (NZ): Resilience to Natures’ Challenges: list with links to publications
- Deep South Science Challenge (NZ): Earth System Modelling and Predictions
- ICOS (Integrated carbon modelling systems): Covid-19
- 2020: UN Emissions Gap Report
- 2020: Freedman & Kaplan; Firenadoes, ember attacks and megafires: Australia is seeing sci-fi weather. Washington Post, Feb 2020.
- 2020: Padrón et al; Observed changes in dry-season water availability attributed to human-induced climate change Nature Geoscience 13, pp477–481
- 2020 NOAA: Climate Change: Ocean Heat Content
- 2020 NOAA: Global Climate Report March 2020
- 2019 NIWA: New Zealand Fluvial and Pluvial Flood Exposure (part of the Deep South Challenge New Zealand)
- 2019 IPCC: The Ocean and Cryosphere in a Changing Climate: Summary for Policymakers
- 2019 UN Environment Programme: Emissions Gap Report
- 2019: WMO Statement on the State of the Global Climate in 2019, World Meteorological Organisation, WMO-No. 1248
- 2019: Salinger et al; The unprecedented coupled ocean-atmosphere summer heatwave in the New Zealand region 2017/18: drivers, mechanisms and impacts Environmental Research Letters 14/4
- 2019: Cheng et al; How fast are the oceans warming? Science 363/6423 pp128-129
- 2018 National Geographic: Half of the Great Barrier Reef Is Dead
- 2014 IPCC 5th assessment Report AR5: Australasia
- 2013/2014 IPCC 5th Assessment Report AR5 (full)