Heat extremes signalled for Wellington

Scientists have calculated dates when they say temperatures for cities around the world will be permanently above historical extremes, and for Wellington that year could be 2041.

The study did not look at any other places in New Zealand, but did do the calculations for several Australian cities, as well as many other centres around the world. 

For Sydney the date could be as early as 2038, for Melbourne it could be 2045, and for Perth and Brisbane 2042.

Those dates are reached assuming a business-as-usual scenario.

With a concerted effort to stabilise carbon dioxide emissions, the University of Hawaii researchers came up with a date for Wellington of 2070, with 2052 for Sydney, 2070 for Brisbane, 2072 for Perth and 2073 for Melbourne.

The index developed by the researchers uses minimum and maximum temperatures from 1860 to 2005 to define the bounds of historical climate variability at various locations.

They then took projections for the next 100 years to identify the year in which future temperature at any given location will shift completely outside the limits of historical precedents.

They called that date the year of "climate departure".

The data came from 39 earth system models developed by 21 climate centres in 12 countries, the University of Hawaii said.

The findings predicted that for the globe as a whole, within 35 years even the lowest monthly dips in temperatures would be warmer than those experienced in the past 150 years.

Under the business-as-usual scenario, the global mean year for a "radically different climate" would be 2047.

In the tropics it would be 2038, and for all other latitudes 2053, the researchers said. In Manokwari in Indonesia the date is as early as 2020, and even with greater efforts to control carbon dioxide would be just five years later.

"These results should not be reason to give up," Camilo Mora, lead author of the study which has been published in Nature, said.

"Rather, they should encourage us to reduce emissions and slow the rate of climate change. This can buy time for species, ecosystems, and ourselves to adapt to the coming changes."