A climate change assessment shows temperatures in the Bay of Plenty are expected to be about 1.2 degrees warmer in 2040 than they were in 1990.
The Bay of Plenty Regional Council’s strategy, policy and planning committee has heard that by 2090 it’s expected to warm by between 2.7 degrees under a low emission scenario, and 3.6 degrees under a high emission scenario.
Climate scientist Georgina Griffiths says hot days – 25 degrees or more – are tipped to become the summer norm by the end of the century.
Whakatane, which gets about 22 hot days a year, may have between 80 and 100 hot days by 2090.
Rotorua, with about 12 hot days a year, can expect to get between 50 and 60 under a high emissions scenario.
Georgina says there was no longer any doubt the Earth’s climate is warming.
Despite the cooling effects of a strong La Nina, 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.
Georgina says New Zealand temperature records show there has been an increase of about one degree over the last 100 years.
She says at Moturiki Island, off Mount Maunganui, sea levels have risen 11cm since 1950; an average rise of 1.9mm a year.
As temperatures rise, scientists expect New Zealand’s wind patterns to shift, which will also affect future rainfall.
Georgina says 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 the future, says Georgina.
The region is predicted to 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.
Georgina says 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, she says.
Opotiki 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.
Current predictions are for a sea-level rise of 50-80cm 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 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 Nina and El Nino, and Georgina says all the possibilities pointed to the same general warming trend.