Demographic tectonic plates are moving beneath our feet and creating a new political landscape that our leaders don’t yet quite know how to navigate.

A decline in primary support for both the Labor and Liberal-National Coalition parties in the past three decades has a multitude of explanations, but one of them has major implications for the kind of governments that are likely to form over the next three.

The power of the majority-conservative boomer and interwar voting bloc is dying, quite literally, and being replaced on electoral rolls at-pace by younger migrants and gen Z voters. And they are voting very differently.

At the last election and in public polls since, these younger voters, and in particular those born since the late 1990s, are roughly as likely to vote for the Greens as the Liberal-National Coalition. It’s an undeniable left-right generational divide.

With millennials and gen Z on track to make up half the voting population by the end of this decade, and with concentrations of progressive voters in inner-city electorates, the likelihood of routine minority or Greens-Labor governments at both state and federal levels is increasing.

This will present as an existential challenge for all the “major” parties, Greens included, because the current playbook for how leaders handle the parliamentary and electoral contests between them will become useless.

Yes, there will be popular and unpopular leaders, major events, disruptions, and other ephemeral factors that deliver victories and defeats for all sides. But an underlying demographic handicap for conservative parties, if it is locked in, will shape every election for the next 30 years.

There is good evidence to suggest it will be. Analysis from Matthew Taylor at the Centre for Independent Studies of ANU’s election study data suggests that millennial and gen Z voters are not becoming more conservative as they age, as we might expect based on the experience of gen X and boomers.

While there is no guarantee of this continuing, a long-term strategy for understanding and harnessing it would seem an urgent priority for all political parties.

Labor and the Greens must reset their relationship. They must behave as competitors for public support, not opponents, if they are to have any hope of forming regular stable governments together.

For many in Labor, this is a highly emotional process. Certain traumas from previous Greens-Labor conflicts make trigger warnings necessary in day-to-day political conversations. Anyone care for a carbon pollution reduction scheme analysis? Definitely not.

The recent decision by Labor in Tasmania to not even attempt to form government was presumably based on the thinking that dealing with the Greens would make future majority government less achievable. But this ship may have already sailed and be impossible for a generation. This could be difficult to accept.

For the Greens, it may be even more difficult. Fundamental questions around the nature of government, mandates and models for power-sharing will challenge its platform of ambitious and urgent reforms.

Australia has already seen several examples of Greens-Labor governments via accords, agreements and even examples of Greens cabinet ministers – but most thus far have at the very least helped make the re-election of a progressive government more “complicated”.

Younger voters are by no means rusted onto the left. They can’t be taken for granted, and similar democracies around the world have shown how economic pain can translate to voting behaviour in different ways.

They will punish governments, and parties, that ignore their concerns. They will do it according to a set of criteria that is more about economic realities than ideology.

In the 1990s John Howard helped shift the identity of many blue-collar workers, who felt abandoned by Labor, into aspiring small businesspeople using conservative policies to promote individuals in the tax and property systems. Thirty years later, a similar strategy could shift younger voters away from their current trajectory.

Alternatively, self-harming behaviour on the left might be conservatives’ best chance of a turnaround.

For Labor, controlling the “sensible centre” will be self-harming if it is not combined with solutions that deliver tangible economic outcomes for younger people. For the Greens, its adjustment to a larger role in government will present various opportunities for implosion and explosion. And there is as much danger for it in resolving economic problems as there is for any other party.

The map that can help political parties navigate this new political landscape will be drawn by looking forward. The path will be based on analysis of where the demographics and the challenges of the next decades are taking us – not solely with lessons from the conflicts of the past.

Peter Stahel is a former Greens adviser and a director and co-owner of Essential, a progressive research and communications company