Such soul-searching has actually been the subject of debate since the party's inception in 1990. The discussion has become almost subliminal, resurfacing periodically for another round before resettling to the default position.
The default is that sustainability isn't possible on a small planet with an ecological overshoot unless resources are shared more equitably. This requires a left-of-centre philosophical stance, albeit social-democratic in spirit rather than socialist. Within that, the argumentation tugs towards both left and centre.
The competing philosophy is that sustainability is independent of resource-sharing. This confines the meaning of the term strictly to ecological sustainability. It's possible for a society, global or national, to be unequal in socio-economic terms yet ecologically sustainable - humanity's footprint remaining within the planetary capacity.
This allows adherents to reach a soft centre-right stance and on specific issues even far-right libertarian. It distinguishes, however, between neo-liberal global corporatism and environmentally friendly, profit-making business.
It thereby avoids the Cold War snare of whether "capitalism" has a positive, neutral or negative influence on the environment.
So it essentially becomes a question of what universal belief system is right for the age. Claire Browning, for example, argued in 2012 on the 40th anniversary of the Values Party that, far from departing from core belief, Green Party principles can rest on green values that are capable of reaching out to everyone - necessarily the case for a sustainable world.
Similarly Vernon Tava, in a post-election article, calls for sustainability to become the central organising principle of the party's thought and action, while yet acknowledging that this has economic, social and cultural aspects as well as environmental.
The NZ Green Party has four principles in its charter: ecological wisdom, social responsibility, appropriate decision-making, and non-violence. The reasoning is that each principle flows with logical necessity from the previous one. This implies that sustainability is the primary principle but this is disavowed. All are claimed to be equal; each a necessary condition of a better society.
The debate is not clarified by the fact that the Global Greens have six principles in their charter: ecological wisdom, social justice, participatory democracy, non-violence, sustainability, and respect for diversity. These were adopted at the first Congress (2001) by 800 delegates from 72 countries. It has never been explained how the global and national (NZ) paradigms interrelate.
In particular, the stand-off between social justice and social responsibility is problematic. The default position is that social justice sanctions policy on the left. But as Glenys MacLellan noted in an article a few years back, social responsibility promotes individual obligation - environmental stewardship and respect for society. Social responsibility is more centrist - and politically unifying across parties.
Much of the debate - criticism from outside and the Green response - derives from different assumptions.
The response presumes the party must adhere to its base, thereby confining the reasoning to refutation and defence.
The criticism presumes the party must reach out to a broader voting niche, inviting a re-examination of its current philosophical stance.
For what it's worth, my view is that the emerging debate reflects an underlying confusion. As a new MP in '09, I advanced the thought that we lack the conceptual tools today to understand 21st century politics ("Time for a New Approach"; the Press, June 16, 2009).
I argued that exclusive reliance on the left-right axis for political analysis is outmoded and suffocating. We need a vertical sustainability axis by which we can be judged - citizens, politicians, parties, governments, countries, humanity.
This would have a dramatic impact on politics. Sustainability, the reasoning goes, is different in kind, not just degree, from the socio-economic argumentation of the left-right kind. It is a different worldview. The horizontal axis is prescriptive; it focuses on how we live, today. The vertical axis is imperative; it focuses on whether we shall live, tomorrow. The vertical axis of sustainability allows us to move more freely along the left-right axis in analysis and prescription.
I contend that the vertical axis of sustainability has to be the primary analytical tool for philosophical positioning in the 21st century, and that the left-right axis is a secondary tool.
If we continue with an excessive focus on freedom versus equality, of market efficiency versus social fairness, and we assign the imperative of sustainability to secondary status, we shall continue to degrade, and ultimately destroy, our planet.
Placing the Green Party solely on the left-right axis is intrinsically impossible. It is like a clock in a Dali painting, without depth-of-field. Only when the Green Party is positioned on the vertical axis will its "positioning" and its "future" come truly to light.
In taking my third parliamentary oath in the 51st Parliament shortly, I shall be swearing to reach across the traditional political divide to embrace colleagues from all parties in promoting green values and seeking common ground among us all. We do, after all, share the same planet.
Dr Kennedy Graham has just been re-elected as a Green list MP.
