New Zealand’s climate varies from year to year from 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 changes 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 reported findings in 1990, 1995 and 2001.
Projections developed by the Intergovernmental Panel on Climate Change (IPCC) suggest that between 1990 and 2100 the average surface temperature around the world will increase by 1.4–5.8°C. This rate of warming is probably without precedent during at least the last 10,000 years. This same period will also see increases and decreases in annual rainfall (depending on location) of 5–20%, a rise in global mean sea level of 9–88 centimetres, and the continued widespread retreat of glaciers. These changes will bring a range of beneficial and adverse effects to environmental and socio-economic systems.
The range of predicted changes is broad, for two reasons:
- It reflects the incomplete knowledge of 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 scenarios for New Zealand’s climate. One study completed by the National Institute of Water and Atmospheric Research for the Ministry for the Environment Climate Change Office concluded that if future greenhouse gas emissions were in the middle of the range projected by the IPCC, it was likely that New Zealand's mean temperature would rise by up to 2°C by the 2080s. Other likely changes included a rise in sea level between 9 and 88 centimetres, increased rainfall on the south and west coupled with a decrease in the north and east, long-term reduction in glacier length, and a greater westerly windflow across New Zealand.
People, land and agriculture
With changing climate, some crops may no longer be grown in some areas. Health risks could change. Local government may alter their regulations for building development and use of water resources. For pastoral farming, increased droughts expected on the east of both islands and in Central Otago could lead to a reduction in 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 kiwifruit production in the Bay of Plenty in the second half of this century.
Acknowledgements to David Wratt