What will Auckland's 2050 climate feel like?

Climate change could heat up Auckland's average temperatures to those of Buenos Aires' today by 2050, a newly-published index suggests. Photo / Supplied

By 2050 climate change could heat up Auckland's average temperatures to those of Buenos Aires' today, a newly published index suggests.

A comparison of 85 cities – published by apartment rentals platform, Nestpick, with input by international climate scientists – projected the city's average temperature moving from 15.2C now to 17.2C by mid-century.

Auckland's potential sea-level rise impact by 2050 – using a score of zero to 100 – was set at a comparatively low 4.56, while there was also a modest increase in water shortage.

By contrast, Bangkok was projected to experience greatest climate change by 2050, with the highest risk of flooding from rising sea-levels and a temperature increase of 1.67C.

Nairobi in Kenya could experience the biggest overall climate shift by 2050, moving from a temperate humid warm summer climate to a tropical savanna wet summer climate type, and a 2.31C temperature increase.

And Melbourne could experience the greatest water-stress increase, with demand expected to be double the supply by 2040.

Ho Chi Minh City in Vietnam, and Amsterdam in the Netherlands were the second and third cities respectively potentially set to experience the greatest climate shift by 2050.

Of the 85 cities compared, Auckland ranked at 49 for its shift across all indicators – and at 40 for the temperature shift alone.

The index follows a similar comparison – and developed by one of the scientists that Nestpick consulted – which suggested temperatures in Auckland by mid-century could resemble today's temperatures in Sydney and Buenos Aires.

Auckland's annual rainfall would drop from 1319mm now to 1261mm in 2050, that report found, while January's mean maximum temperature would rise from 23.7C to 26.5C.

Wellington, meanwhile, would move from having an annual mean of 13.1C to one of 15C – and its average rainfall would also decrease, from 1324mm to 1130mm.

The capital's mean maximum temperature would shoot up from 19.7C to 24C – while the minimum of its coldest month would go from 5.6C to 7.2C.

But Victoria University of Wellington climate scientist Professor James Renwick said some context needed to be put around those types of comparisons.

"It's only 30 years we're talking about - and there are quite a lot of natural ups and downs in the climate and in 30 years, the climate-change signal may not be that dramatic," he said.

"But with the scenario this new index has chosen – that's RCP 4.5, or where we will have stabilised greenhouse-gas concentrations by the end of the century – there would still be something like another degree of warming by the middle of the century.

"So that's as much as we've had in the last 100 years, and that would be significant."

Renwick added that Auckland's maritime geography needed to be considered.

"Could Auckland become like Sydney? Yes, in the sense of average temperatures. But when it comes to the sorts of weather events these cities see, Auckland is never going to be like Sydney, just because of the geography.

"So you need to take this stuff with a grain of salt."

Renwick also questioned the new index's water stress score, which he suspected of being too low.

"Auckland may not be as badly off as Melbourne for water in the future, but the northern North Island is expected to dry out further over coming decades - so I imagine water availability is going to be a more pressing issue for Auckland as time goes on."

Projections previously made for Auckland included the average temperatures becoming anywhere between 0.7C and 3.1C warmer by 2090, along with anywhere from 11 to 70 extra days per year where maximum temperatures exceeded 25C.

Along with that would come more frequent heatwaves, like that which hit the city this year, more frequent extreme rainfall events, and a sea level projected to be 15cm to 30cm higher by 2050.

Low-lying parts of the city – including the CBD, eastern bays, Onehunga, Māngere Bridge, Devonport and Helensville – would be the most vulnerable to inundation.