Climate Change Minister James Shaw was warned emissions target was too ambitious, too expensive

Newshub can reveal the Climate Change Minister was warned his climate target was too ambitious, too expensive and could be setting New Zealand up to fail.

And Treasury warns even a less ambitious goal would lead to either higher taxes or government cuts.

It was the moment Climate Change Minister James Shaw had worked for. On the stage in Glasgow, he showed off Aotearoa's upgraded climate commitments to the world.

Glasgow was the biggest climate summit since the Paris Agreement in 2015. And just before Shaw left to attend it, he promised we'd cut our greenhouse gas emissions by 50 percent by 2030.

But the Government uses two different measures - what was used on the international stage is a 'point-year target'. That's the 50 percent by 2030.

Confusingly the government also expresses this as a multiyear budget which means that 50 percent equates to 41 percent from 2021-2030.

"We did go to the point that we felt that we were able to do," he says.

But even though the target is 41 per cent, Newshub can reveal his own officials don't think we were able to go beyond 40 percent.

In advice to Shaw, the Ministry for the Environment - the climate change experts - said cutting emissions beyond even 40 percent has significant uncertainties and risks of non-delivery.

The Treasury - the finance experts - said cutting by even 45 percent had significant fiscal and economic risk that will have to be met by higher taxes and/or the offsetting of other government expenditure.

And MBIE - the super-business ministry - was concerned there'd been insufficient analysis undertaken to understand the fiscal and social impacts of a 45 percent reduction.

Shaw believes the target is achievable. However ACT leader David Seymour disagrees.

"A 40 percent reduction is not achievable - they went out there and did 50 percent. It's just pure PR and some would say BS," he says.

Shaw said Seymour didn't understand the reduction targets.

“Our climate change targets are not just achievable, they are essential. The next decade is make or break for the planet – we need to focus all our energies on finding every way we can to lower emissions and limit warming.

“Mr Seymour's interpretation of official advice is, unsurprisingly, incorrect. When represented in like for like terms, the advice from MfE was actually very close to Cabinet's eventual decision.

“I acknowledge climate policy is complicated, but I think it's fair to say if you don't understand it, you're better off not commenting.”

Climate scientist Lauren Vargo said having ambitious targets is important.

"I think having high ambitious goals when it comes to climate change is good. Mitigating climate change is very important," she says.

But those ambitious goals come at a cost - two-thirds of our targeted emission reductions won't be achieved here in New Zealand.

Instead, we're going to have to buy overseas credits as well as reducing our own emissions to meet our goal.

"Not doing anything about this will probably be more costly in the long run," Vargo warns.

How much we cut emissions by is a political decision.

Shaw actually wanted more - 45 percent - and after months of negotiations, he got Cabinet to the 41 percent experts called unachievable.

The plan for how we achieve the supposedly impossible will be revealed in April.