New Zealand’s climate varies from year to year thanks to natural processes. Some parts of the country, for example, have dry summers and autumns when an El Niño weather pattern is present. Natural fluctuations need to be considered alongside human-created climate change when developing plans and policies. Beyond the next few decades, however, global warming, caused mostly by human activity, will begin to dominate. To understand the range of possibilities for future climate in New Zealand, it is helpful to first look at projections of global change.
The Intergovernmental Panel on Climate Change (IPCC) was established in 1988 by the World Meteorological Organisation and the United Nations Environment Programme. It analyses the most up-to-date research on climate change, and has reported its findings in 1990, 1995, 2001, 2007 and 2014. The Sixth Assessment Report from the IPCC will be published in 2021.
Projections developed by the Intergovernmental Panel on Climate Change (IPCC) suggest that if our emissions continue to grow at the current rate, the average surface temperature around the world will increase by 3.7–4.8°C between 1990 and 2100. This rate of warming is probably without precedent during at least the last 10,000 years. The same period will also see a rise in global mean sea level of between 61 and 110 centimetres, the continued widespread retreat of glaciers, and significant increases or decreases in annual rainfall depending on location. These changes will bring a range of adverse and some beneficial effects to environmental and socio-economic systems.
The range of predicted changes is broad, for two reasons:
- It reflects incomplete knowledge about how to model climate systems and the intrinsically chaotic behaviour of the systems themselves.
- The scale and range of future greenhouse gas emissions depend on future political and socio-economic actions.
New Zealand climate changes
There are a number of potential changes for New Zealand’s climate. In a 2018 study completed by the National Institute of Water and Atmospheric Research for the Ministry for the Environment, the mid-range estimate for projected New Zealand temperature change was an expected increase of 1.4°C by 2090 relative to the period 1986–2005. Other likely changes included a rise in sea level above 1990s levels of between 46 and 105 centimetres by 2100, increased rainfall in the south and west of the country coupled with a decrease in the north and east, a long-term reduction in glacier length and ice thickness, and an increased westerly windflow across New Zealand.
People, land and agriculture
With a changing climate, some crops may no longer be grown in some areas. Health risks could change. Local authorities may alter their regulations controlling building development and the use of water resources. For pastoral farming, increased droughts expected in the east of both islands and in Central Otago could lead to reduced grass growth. Subtropical grasses are expected to spread south, with pastures extending to higher ground. Warming will increase the incidence of agricultural pests and diseases, but it will also allow arable and fruit crops to spread south. One study suggests that warming in winter could begin to restrict Hayward kiwifruit production in Bay of Plenty after 2050.
Acknowledgements to David Wratt