More work is needed to better understand how climate change will affect New Zealand at a regional level, a new report says.
The new report released today by the Office of the Prime Minister's Chief Science Advisory Committee examines climate-driven changes that have been observed within New Zealand to date, along with probable impacts over the next 40 years.
"We have worked closely with scientific experts from across the relevant crown research institutes, university departments and ministries to pull together the latest knowledge on what New Zealanders can expect as the most likely scenarios in the coming decades," the Prime Minister's chief science adviser, Sir Peter Gluckman said.
It highlighted how regional impacts will vary and that it was important to look at seasonal patterns and the degree and frequency of extreme events rather than simply at average changes.
The report found impact of predicted changes in wind patterns, precipitation, and ocean chemistry could be expected to have significant impacts on the environment and thus many primary industries.
However, these changes generally were not expected to be uniform across New Zealand.
While pH changes would be overall greater in cooler waters, upwelling areas in the North Island such as the Hauraki Gulf were more vulnerable to a given change, and in the South Island, impact in the high-latitude Southern Ocean was expected first, from 2040 onwards.
The nationwide mid-range of projections was an average temperature increase of 0.9deg by 2040 and 2.1deg by 2090, but these would differ across various regions.
The number of frosts in the Central Plateau would halve by 2100 and in the South Island, frosts were expected to be rare on coastal locations by 2050.
There would be an overall increase in the strongest winter winds by the turn of the next century - in the North Island, this would mean less of a westerly wind component and more easterly episodes, as tropical zones moved south in summer.
In the South Island, there would be more frequent and stronger westerlies during winter and spring.
The report stated there would be little change in mean precipitation for all of New Zealand, but a large geographical variation.
This would mean overall precipitation decreases in the east of the North Island by up to 5 per cent by 2040, with smaller changes in the west, while increases in the west of the South Island by 5 per cent and smaller decreases in the east.
The entire country would see heavier and more frequent extreme rainfalls, but also more droughts - on average, there would be two or more extra weeks of drought annually by 2050 for much of the North Island and eastern South Island.
In the west of the North Island, rainfall in summer and autumn would decrease, but would increase in spring and winter by up to 5 per cent.
In the east of the island - including Gisborne and Hawkes Bay - rainfall levels in winter and spring would drop by up to 10 per cent.
There would be more precipitation in the west and south of the South Island, but reduced precipitation in the east, with heavier and more frequent extreme rainfalls.
Among its conclusions, the report noted further work was required to understand better regional interactions of systems around New Zealand to improve the quality of estimates and to test models for changes in temperature more extreme than the 2oC relative to pre-industrial levels, which had been the predominant focus to date.
"Indeed progress in reducing emissions at the global level has been minimal and thus higher temperature predictions are now more likely and need to be planned for."
New Zealand scientists were engaged in this "urgent need" for further research, and several of the recently-announced National Science Challenges would advance the understandings and implications of climate change.
But suggesting specific adaptive strategies was beyond the scope of the report.
"Science can provide analysis of current and future risks relating to climate change and can indicate the issues that local and national governments need to consider; however responses involve judgments based on a broader range of factors and cannot be based on science alone," Sir Peter said.