As the debate over the planet's shifting climate becomes ever more urgent and experts and lobbyists spar over how badly it will affect us, where it will hit hardest and when, the fine details of climate change science remain, for defence planners, largely irrelevant.

Their business is to plan for contingencies – especially the unlikely ones – and all potential catastrophes, climate-driven or otherwise, demand their attention.

However, the complex chain of events that a warming climate could set in motion makes the global security picture 30 to 50 years from now a particularly challenging one for governments and militaries to legislate for.

Nor is the worsening climate the only factor that promises to reframe the security debate: the continuing explosion in global demand for essential resources such as food, water and oil – coming just as our planet's ability to deliver many of these materials is passing its peak – threatens, in harness with the climate crisis, to pose challenges to security of an order not previously faced in modern times.

Early glimpses of the security consequences of a changing climate can already be seen. The evacuation of the 1,400 residents of Papua New Guinea's Carteret Islands - the world's first climate change refugees, according to the UN - due to rising sea levels offers a sobering vision of the future for other Pacific island nations and for coastal populations around the world.

Source: Jane's news