Charging 15c for plastic bags may make people think twice about throwing them away - but would New Zealanders like it, and what are the likely unintended consequences?
Green MP Denise Roche has drafted a bill to charge for plastic bags in a bid to reduce the vast number thrown out each year. The bill has gone into the ballot for members' bills.
The proposed levy - which would be charged on single-use plastic bags at the check-out - is a key part of the party's war on waste.
Ms Roche told RNZ's Sunday Morning that despite growing numbers of people bringing their own shopping bags, New Zealanders still use 1.6 billion single-use plastic bags a year.
But ACT party leader David Seymour said although well intended, her bill would actually cause more harm than good.
Ms Roche said 15 cents a bag was a good starting point to change people's habits.
"They're really handy, they're free, they're everywhere - and their impact on the marine environment is devastating.
"About 100,000 marine animals killed every year from plastic, and plastic bags make up a big proportion of that."
She said it was a "gateway" issue - although not the biggest item in the landfill in terms of weight, it is something people understand and a big symbol of waste.
Why not just ban plastic bags?
"People don't respond very well to bans, and with a charge you trigger people's voluntary behaviour," Ms Roche said.
She insisted retailers would be happy to introduce a charge and some had already started.
"In fact, where I live on Waiheke Island our supermarket is (charging for plastic bags). It's the first one in a chain to do that, and it's because of community pressure."
She said the major supermarket chains had told her they would be happy to charge for plastic bags, but they wouldn't do it voluntarily.
Ms Roche said competition was so stiff, they would bring in a charge only if all retailers were required to.
"If you had every supermarket doing it that would level the playing field."
Although the Grocery Council was not keen on the idea of a charge for plastic bags, Ms Roche said retailers were very supportive and increasingly saw their environmental impact as part of their marketing.
UK model 'a success'
Ms Roche noted that some Australian states had successfully introduced a plastic bag levy, but she said her bill is based on the United Kingdom's introduction of a 5 pence (8.5 cent) charge a year ago.
"They have had an 85 percent reduction in bag use in six months and have created £30 billion ($NZ51.2bn), which is donated to charity."
Recognising that in some parts of the world - such as Austin, Texas - single-use plastic bags had been replaced by even more wasteful multiple-use plastic bags, Ms Roche said she favoured those made of cloth or string.
"In New Zealand, we are more clued up around the kind of tricks the packaging industry would use to try and get us to use more plastic."
ACT - Green Party 'lazy'
David Seymour of the ACT Party said where plastic bag levies had been tried they had in some cases worked, but there were unintended consequences, which the Greens should consider.
"Okay you reduce reusable plastic bags, but what happens next?"
He said in the city of Austin, in Texas, retailers started using thicker plastic bags that were not captured by the rule but increased the amount of plastic being used.
And there were even more unfortunate consequences, he said.
"In San Diego, the George Mason University study found there was an increase in food-borne illness, and the hypothesis is that that was the result of people who wouldn't normally have reusable bags being forced to use them - leaving them in a car in a hot summer, perhaps with a little bit of chicken juice or something that had seeped out, and it actually made a lot of people sick."
Mr Seymour said to have the same environmental impact, a cotton bag would have to be used 173 times "which sounds a little ambitious".
Although Mr Seymour admitted that a levy could lead to an 80 percent reduction in their use, he suggested the overall effect would be minimal.
Plastic bags make up just 0.25 percent of plastic waste in New Zealand he said. And - based on British figures - although they made up a disproportionate amount of litter (2 percent), charging for them would not greatly influence the amount of litter either.
"Even if you have an 80 percent reduction that means you are going to go from 2 percent down to 0.4 percent."
The Green Party's Waste Minimisation (Single-use Plastic Bag) Amendment Bill was put into the ballot on 17 October.
1.6 billion plastic bags in the NZ environment
Plastic bags comprise 0.2 percent of landfill waste by weight
The Warehouse charges 10 cents per plastic bag with proceeds to charity
Pak'n'Save charges 5 cents per plastic bag
UK levy resulted in an 85 percent reduction in plastic bag use
According to the Huffington Post, the George Mason study was "harshly criticised by environmentalists, as its authors received monetary support from the American Chemistry Council, a trade group representing the interests of plastic bag manufacturers".