With the Green Party's greatest triumph comes the biggest threat to its survival.
For 20 years, National and Labour-led Governments have bickered over climate-change policy.
Roughly, Labour Governments have wanted to do a bit more and National Governments a bit less. But, as broad-based parties, both have had to take the wider social and economic context into account.
Only the Greens have had the luxury of a purist message, ignoring the domestic economic consequences of climate-change proposals and even the fact that displacement of New Zealand food, steel, aluminium or natural gas production by dirtier foreign operations would in fact increase overall global emissions.
Such purism has been electorally advantageous. The Greens are the most secure of all the smaller parties above MMP's 5 per cent threshold despite several leadership transitions and 2017's Metiria Turei welfare scandal.
The question is whether this political success has hitherto counted for anything.
Despite Helen Clark's soaring rhetoric in 2007 about New Zealand becoming the world's first carbon neutral country by 2020 and Jacinda Ardern's call for a "nuclear-free moment", New Zealand's only genuinely effective climate-change policy this century was Tim Groser's Global Research Alliance on Agricultural Greenhouse Gases. That alliance, which Groser launched in Copenhagen in 2009, now has 61 countries involved from all regions of the world.
With last week's Zero Carbon Act, Greens co-leader James Shaw has similarly secured his place in history by building policy consensus among National, Labour, NZ First and his own party.
Of the five parties in Parliament, only Act now offers a home for those who doubt the reality of climate change, or who accept it but believe there is nothing New Zealand can or should do to mitigate it, with the best domestic priority being adaptation.
Like this week's triumph by Act's David Seymour on euthanasia, actually achieving something he genuinely believes in sets Shaw apart from most MPs and ministers, who simply take the salary and preside over the status quo.
But the problem, electorally, is that the Greens have lost their most powerful issue.
Come election time, Shaw and Ardern may wax lyrical about the new legislation and the Climate Change Commission it sets up, but Simon Bridges and Winston Peters will both be able to say, "yep, that's my policy too" and move on to immigration, infrastructure, housing or the economy.
As a former Climate Change Minister who promised National would take the issue seriously when he became leader in February 2018, it is possible Bridges is sincere.
In backing the bill, the Opposition leader has foregone the exquisite opportunity to declare Ardern's "year of delivery" a totally unmitigated failure.
National and NZ First are chasing the same provincial vote and so are joined at the hip on issues that worry farmers and agriculture support industries. Had Bridges defected from Shaw's consensus, Peters would have too, and the bill would have been defeated.
Whether out of genuine conviction, cynical political calculation or both, Bridges has therefore chosen to give Ardern a significant short-term win, but that only underlines how powerfully it is in National's interests to remove climate change from the mainstream political debate, while allowing its coalition partner Act to pick up the residual sceptical or denialist vote.
With multi-party consensus, those who worry about climate change now have no more reason to vote for the Greens than for Labour, National or NZ First.
Green activists are not unaware of this. For them, Shaw has always been in the wrong party, having even helped in National's 1996 campaign for his friend, Wellington Central candidate Mark Thomas.
Shaw was motivated to join the Greens when he came to see climate change as a genuinely existential threat while working on the subject at PricewaterhouseCoopers in London.
His life's mission is to stop climate change using any means possible, even if that means compromising with the capitalist system and adopting western science, such as genetic modification or, elsewhere, nuclear power.
This is not the outlook of the Green Party base. To them, climate change is merely the latest symptom of the twin disasters of capitalism and western science. Solving climate change without eliminating the hegemony of capitalism and science is therefore not just pointless but even counterproductive, since it will mean an even worse problem will come along soon.
Better that humankind learns its lesson about capitalism and science through a climate disaster in the next few decades than wait for whatever worse catastrophe looms over the horizon.
Some in Green Party circles believe that merely communicating this truth will grow its vote but others are more realistic, believing the party needs bourgeois environmentalists as part of a broader church to remain above 5 per cent.
To the first group, Shaw's alliance with capitalism and western science is morally reprehensible and doomed to be socially, environmentally and economically catastrophic.
To the second, his collaboration gives permission for some of the usual Green vote to float off to National, Labour and NZ First, and perhaps a handful to the new Sustainability NZ Party.
If the factions can agree on anything, it is that his compromise risks the survival of the party in Parliament.
To Shaw, who not only believes his Zero Carbon Act will eliminate New Zealand's emissions but will inspire the rest of the world to follow, the end of his own political career and ongoing parliamentary representation for the party he co-leads would be a small price to pay for saving the planet.
But to those who understand that green philosophy is not about merely solving the environmental problem of the day but realising the agrarian socialism of Henry David Thoreau, Mao Zedong and the Khmer Rouge, Shaw's deal with Ardern, Bridges and Peters marks him as the ultimate Quisling. More activists can be expected to leave the party.
- Matthew Hooton is an Auckland based public relation consultant and lobbyist.