Richard Di Natale’s address to the Lowy Institute was something of a landmark in the evolution of the Australian Greens’ policy agenda. For too long the Greens have been preoccupied with the touchy-feely end of the policy spectrum, and unwilling to dirty their hands in the polluted waters of traditional security issues.

The position outlined by Di Natale on foreign policy and defence may not have been entirely unproblematic, but it compares favourably with anything on offer from the major parties. The central message from his talk – that Australia needs a serious and extensive debate on the rationale for, and basis of, defence policy – looks irrefutable, even if it’s unlikely to be acted on.

If there’s one thing the Greens are right about, however, it’s that climate change is ultimately the biggest threat to security this country or any other will face in the long term. That, unfortunately, is the problem for parties like the Greens. Even though the consequences of climate change are becoming all too apparent, they unfold relatively slowly.

Put simply, the management of environmental problems is fundamentally at odds with democratic processes where the focus of attention is almost exclusively on the immediate and the ephemeral. One of the reasons that a serious debate about the nature of security is so difficult is that the problems are complex and unlikely to come to a head within Australia’s ludicrously truncated electoral cycle.

An added and exclusively Australian reason for the lack of debate about security is the sacrosanct nature of the alliance with the US. Even raising this as an issue not only invites accusations of strategic illiteracy, but also risks confirming the Greens’ reputation as limp-wristed liberals with no understanding of the nature of geopolitics.

The remarkably high levels of support within the Australian public for the ANZUS alliance mean this is what Sir Humphrey Appleby might have called a “very brave” policy. But given that the whole thrust of Di Natale’s address was to highlight the need for leadership and original thought on such issues, such political risks rather go with the territory he is staking out.

There is little doubt that the major parties will not respond positively to the Greens’ call for debate. It is not simply the rather brutal, point-scoring context of electoral politics that ensures this, however. Even in less politically charged times the conventional wisdom is so entrenched on defence issues that an uncritical consensus carries the day. Little wonder the general public goes along.

Predictably – and rightly – Di Natale was pressed on some suitably hot-button defence issues. What do we do about an increasingly aggressive China, came the inevitable question. The answer was not entirely convincing. Pointing out that nobody else has a good answer either was not an unreasonable observation, but one that will undoubtedly be taken out of context.

Let’s hope that Bill Shorten and Malcolm Turnbull are encouraged to answer the same sorts of questions about the rationale for, and expense of, the alliance, the way we might deal with China’s expansionist ambitions and – most importantly, perhaps – the significance of climate change as the principal threat to long-term global security.

Here the Greens are undoubtedly on surer ground, even if it is difficult to get the electorate to take it seriously as a potential vote-changer – or not until it’s too late, at least.

The other problem with this issue is that the benefits of serious policy innovation are likely to flow to people outside Australia first. Not what you would describe as a surefire vote winner.

This also applies to the Greens’ other great foreign policy weakness as far as the majority of the population seems to be concerned: asylum seekers.

There does seem to be a belated recognition among the Greens’ leadership that outside of their committed supporter base, many in Australia do not share their admirably humanitarian principles. This was true before the migration crisis in Europe forced even the civilised Swedes to abandon their generous policy stance. It is doubly so now.

The reality is that making policies that are actually likely to be implemented is difficult and always involves compromises. This is the essence of the political process, after all. Perhaps the much-decried period of power-sharing with the Gillard government actually did some good after all. The Greens know from direct experience what is involved in negotiating policy development and implementation.

Clearly the Greens are a work-in-progress, but they have developed a degree of professionalism and indeed realism that makes them as credible as their opponents, who generally seem bereft of original policies and determined to relive the debates of the last century.

To judge by the apparent thirst for alternative and creative ideas around the world, the Greens moment may have finally arrived.