Bay of Plenty temperatures are expected to be about 1.2°C warmer in 2040 than it was in 1990, according to a climate change assessment for the region.
This week’s Bay of Plenty Regional Council Strategy, Policy and Planning Committee heard that by 2090, it is expected to warm by between 2.7°C under a low emissions scenario, and 3.6°C under a high emissions scenario.
Senior Climate Scientist Georgina Griffiths said hot days – 25°C or more – are tipped to become the summer norm by the end of the century. Whakatāne, which gets about 22 hot days a year may have between 80 and 100 by 2090. Rotorua, with about 12 hot days a year, can expect to get between 50 and 60 under a high emissions scenario.
She said there was no longer any doubt that the Earth’s climate was warming. Despite the cooling effects of a strong La Niña, 2011 was globally the ninth warmest year since 1880, reinforcing a trend which showed that nine of the 10 warmest years on modern record happened after 2000.
New Zealand temperature records show an increase of around one degree over the last 100 years, and sea levels had risen 11 centimetres since 1950, an average rise of 1.9 millimetres a year, at Moturiki Island, off Mt Maunganui.
As temperatures rise, scientists expect New Zealand’s wind patterns to shift, which will also affect future rainfall.
Warming will be fairly uniform across the region, but not all seasons will warm at the same rate. Autumn and winter are projected to warm slightly more than summer and spring. The warmer air gets, the more moisture it can hold, so rain is likely to fall more heavily in future.
The region will get roughly the same average annual rainfall in 2090 as it does now, but rain may fall at different times, with drier winters and more summer rain, particularly inland. Some areas will get more rain, while others, particularly along the coast, will get less.
The Bay of Plenty will get more easterly winds during summer, and more westerlies over winter, but fewer extreme winds in summer and more in winter.
By 2090, air frosts will be a rare thing in the Bay of Plenty. Ōpōtiki has about five frosts a year, and Rotorua 20, but by the end of the century, Rotorua may have just one a year or none at all and other areas may get a frost only every three years, and fewer cold nights.
Current predictions are for a sea-level rise of between 50 centimetres and 80 centimetres by the 2090s, but they could be higher, meaning more planning requirements for coastal development.
The findings are calculated on a range of emissions scenarios, including very rapid economic growth and global population peaking mid-century, then declining, adoption of new, more efficient technologies, and a more piecemeal response to climate change which slows the uptake of new technologies.
The scientists also considered natural phenomena, such as La Niña and El Niño weather, Ms Griffiths said. All the possibilities pointed to the same general warming trend, she said.