He said to have sustainability built into the Parliament in the long term, an environmentally focused party would - unlike the Green Party - need to work with both sides.
"It can work, obviously, with the left and right - and should, and will have to."
"If you listen to Vernon Tava - and I support this - you have government and you have opposition and if a political party says it's only going to work with one side of that house, then you're not going to get a long-term binding genuine consensus.
"That is required in any country - including New Zealand - for effective long-term or even medium term sustainability: You need environmental philosophy to be placed in the centre and to be working with both left and right."
But this gets things exactly backwards. The problem isn't that the Greens won't work with National - they have done so in the past and have signalled their willingness to do so again. The problem is that National won't work with the Greens. On environmental fundamentals - climate change, rivers, mining - National is utterly opposed to sustainability and Green policy. And that will be the same whether that policy comes from the existing Green Party, or some imaginary "centrist" vehicle.
Until National changes and really accepts sustainability, no green party worthy of the name can support them as a government. And anyone who tells you differently is either a fool, or trying to sell you something.