The war on Iran, which may still be a long way from over, has triggered an energy challenge that highlights the world’s collective failure to face the looming threat of climate disruption. But in a most frightening way, the use of nuclear war has also been explicit and immediate.

This moment now condenses two existential threats – climate disruption and the threat of nuclear war – into one crisis, and one that will remain long after this war subsides.

For more than a decade, I have argued that climate change is not just an environmental concern but a fundamental threat to national and global security. I have pressed governments to conduct rigorous risk assessments, to treat the destabilisation of planetary systems with the same seriousness they apply to military threats, and to act with urgency while there is still time. That argument stands.

This year has seen newly created conditions for nuclear escalation that no responsible security leader can observe in silence. How else can we understand the threat by the US president that “a whole civilisation will die tonight”?

My working life was grounded in security risk assessment. Over 42 years in the Royal Australian Navy, culminating as chief of the defence force, I learned that the first duty of strategic leadership is to call threats clearly, without flinching from inconvenient conclusions. Climate change has been my focus for the past two decades, but nuclear escalation is now also at the forefront of my concerns.

The current situation has several........

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