Temperature to rise
Air temperatures are projected to increase by about:
The full range of projections across scenarios is:
0.2-2.0°C by 2040
0.7-5.1°C by 2090.
A 2°C warming is about the difference in the annual median air temperature between Wellington and Auckland. There will still be variability from year to year – i.e. warmer years and colder years. But an unusually warm year now could be the norm in 30-50 years, and might be considered a very cold year by the end of the century.
Initial simulations from NIWA’s regional climate model suggest large decreases in the number of frost days in the central North Island and in the South Island. For example, the number of frosts in the central plateau of the North Island, away from the alpine areas such as Mt Ruapehu, could more than halve. Currently the plateau gets about 30-40 frost days per year. Under a low-medium emission scenario, this could drop to 5-15 days per year, and even fewer with a medium-high emission scenario, by the end of the 21st century.
NIWA’s initial regional climate model runs also suggest substantial increases in the number of days above 25 °C, particularly at already warm northern sites. For example, the number of hot days in Auckland could double or treble. Currently, the city experiences about 21 days per year above 25°C. By the end of the 21st century, Auckland could experience an extra 40 days or more of such high temperatures under a low-medium scenario, and more than 60 extra days of such temperatures under a medium-high scenario.