Wellington Airport has today revealed its 20-year, $1 billion-plus upgrade, which includes a brand new terminal as well as other developments.

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The airport's chief executive said the upgrade was necessary to ensure the airport could cater for the doubling of passenger numbers by 2040.

Currently, 6.4 million people pass through Wellington Airport every year - though this number has been significantly rising for a time already.

In 20 years' time it's expected about 12 million people will pass through, but chief executive Steve Sanderson said there was no capacity for those future numbers.

The airport is geographically hemmed in between Lyall Bay to the south, Evans Bay to the north, the Miramar Links Golf Club to the east, and a retail park plus some housing to the west.

Mr Sanderson said it was clear where the expansion must go, not that that had made it any easier.

"Wellington Airport operates on the smallest piece of land of 110 hectares," he said. "Compare that to Auckland, which is close to 1600 hectares of land.

"So we've put a lot of thought into that, so the only way we can deal [with that] is to go south and to go east into the golf course. Those discussions with the golf course are well advanced now and we're confident we'll have a commercial deal with them this side of Christmas."

As well as commandeering the back nine of Miramar Links, the upgrade will include a new international terminal, relocating flight catering and rental car facilities to an area in the north, and expanding the western apron for aircraft operations.

All in all, it's a sizable operation, with Mr Sanderson hoping works can begin in early to mid-2021.

"Particularly over the next seven years you'll see the apron and the terminal completed - so at the moment we're just finalising our concepts and our drawings, and we'll take that to full design, and we'd like to start construction within an 18-month period."

A lot of money, but who's going to pay for it?

At $1 billion, the upgrade is also a serious investment for the future.

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Wellington Mayor-elect Andy Foster said the council - which owns a 34 percent stake in the airport - won't be putting any money into the project.

"It's a development that the airport company is planning," he said. "There is no intention to call on the council for any equity injection.

"For us it's: airport - get on and do it. Our role is going to be particularly with things like connections to the airport and Let's Get Wellington Moving is going to be very important there, and any other things in terms of transport around it, we will also have a regulatory role to some degree."

The airport's chief executive has the same idea.

"This is traditionally a debt-funded project and at a current cash flow, so that will be over a long period," Mr Sanderson said.

"It's not unusual for airports to be spending anywhere between $40-$100 million per annum on capital investments. As passenger numbers grow, so do the revenues, and so it becomes an affordable project."

The airport has predicted that as a result of the expansion, the airport will double its economic contribution to the region, from $2.3 billion to $4.3 billion - creating more than 22,000 jobs along the way.

Mr Foster said he was pleased with the plan, adding that it showed confidence in the city's future, planning for more people, and more growth.

But the airport in its current standard is not fit to deal with it, Mr Foster said it was important the airport is an impressive welcome for those visiting the capital.

"You actually have to make sure if you're expecting growth in passenger numbers, you're not just literally packing people in and giving them an unpleasant experience," he said.

"You want them to say: 'Wellington is a good place to visit', and the airport is often the first experience of the city and the last experience of the city."

Plan has wary locals and climate critics already

The plan, entitled "Master Plan 2040", was released today but has already attracted criticism from climate scientists.

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Professor of Physical Geography at Victoria University James Renwick said expanding the airport was not a good call.

"This is really the wrong way to be going," he said. "If we're serious about reducing greenhouse gas emissions and getting on top of climate change, doubling passenger numbers at Wellington airport or any airport really isn't sustainable."

Further to that, Dr Renwick said it was not good that both the number of people and the number of flights were increasing.

"Flying is one of the key ways people and goods are transported around the world today, so we can't just stop.

"But we do have to manage how we fly, and the number of flights that are taken, and we need to be looking at reducing flying rather than increasing."

In response, Mr Sanderson said planes were becoming more fuel-efficient; and Air New Zealand was planning to have electric-powered domestic flights by the mid to the late 2020s.

But for some who work and live near the airport, the expansion is seen as a threat to homes and jobs.

Surf and streetwear company, Backdoor, is located in the retail park to the east of the airport, and could be taken over by the development.

"I definitely would have expected there would have been more information regarding how it's going to affect the retailers", said its manager, Anahera Maaka.

Locals on Lyall Bay also had concerns about how an airport expansion would impact the immediate area.

One said she was concerned the roads would become congested, while another said he hoped it wouldn't affect his dog walks.

The airport said it wanted to hear feedback from local residents, with the consultation period open until 17 November.