Wellington's 2050 climate will resemble Auckland's today – while Auckland will feel more like Sydney, scientists say.

Researchers have illustrated how much hotter the world's major cities will be under a projected mid-century climate.

And while Mission Bay weather in Thorndon might sound appealing, the maps they've created are anything but good news.

The authors of the new study, just published in major scientific journal PLOS One, combined data on 19 climatic variables for 520 cities with a model that optimistically assumed emissions would peak around 2040, and then fall.

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The analysis predicted that by 2050, under this scenario, the climate of 77 per cent of the cities could resemble the current climate of another city more closely than their own.

The current annual mean temperature of Auckland, 15.2C, would climb to 17.2C – comparable to that presently of Sydney, where the mean would in turn shift to 19.5C.

Auckland's annual rainfall would drop from 1319mm now to 1261mm in 2050, 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.

Elsewhere, the study predicted that Madrid's climate would become like that of Marrakech – while London's could be more similar to that of Barcelona, and Seattle's to that of San Francisco.

More generally, the climate of Northern Hemisphere cities was predicted to warm by 2050 to resemble, on average, the climate of cities 1000km further south, with European cities predicted to be on average 3.5C warmer in summer and 4.7C warmer in winter.

Cities in the tropics were predicted to get drier by 2050, with 30 per cent predicted to have arid climates not currently seen on Earth.

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The authors only examined the cities under one predicted climate change scenario, and there were huge uncertainties about how climate change could unfold and how cities could respond to mitigate its effects.

Cities were also matched solely using climate parameters, without taking account of other differences.

Nonetheless, the authors said the "city pairs" they identified might help citizens to visualise the possible effects of climate change.

"Generating an understanding of the shifts in climate conditions of the world's cities is critical if we are to get a global unifying perspective of the impacts of climate change," said lead author Jean-Francois Bastin, of the Swiss Federal Institute of Technology in Zurich.

The study comes as both Auckland and Wellington have declared climate change emergencies.

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.