Auckland is forecast to get hotter and the region's average temperature could increase by up to 3.75C over the next century, a NIWA report says.
If global greenhouse gas emissions continue on their current path, the number of days when the mercury rises above 25C could quadruple, the report says.
Drought and more extreme bursts of rainfall are also predicted, as are rising sea levels, which would have major impacts on coastal communities, infrastructure and habitats.
Ocean acidification would affect ocean productivity and the development of marine species, while increasing sea surface temperature is likely to encourage non-native marine species to establish and proliferate.
The report was commissioned by Auckland Council and council-controlled organisations to model and analyse Auckland-specific climate projections.
Council chief sustainability officer John Mauro says better information about how Auckland's climate is changing will help in making more effective decisions about the region's future.