The Department of Defence has spelled out clearly to a Senate enquiry that climate change is increasing demand and will create "concurrency pressures" for the Australian Defence Force as a rise in disaster relief operations continues.

"The ADF is … built around the most demanding and most complex of its roles, the warfighting role," the Defence Department told a Senate enquiry into climate change and security last month.

"Due to the nature of its capabilities it is able to make a contribution to Humanitarian Assistance and Disaster Relief (HADR), though the force is not structured around this task."

At the moment, while Australia has no large-scale war commitments, Defence says its can handle the workload.

"However, the forecast level of commitment may create concurrency pressures for Defence from as early as the middle of the next decade, or earlier if climate change-related impacts on security threats accelerate."

A graph supplied to the Senate shows the number of ADF disaster missions increasing alongside the number of disasters across the Asia-Pacific. ( Supplied: Department of Defence )

Defence said climate change could magnify regional instabilities, causing security problems for Australia.

"Climate change can act as a 'threat multiplier'."

"Climate change may also eventually contribute to greater irregular migration pressure in vulnerable countries to Australia's north, potentially becoming a substantial security threat for Australia."

The Senate report concluded that "the consensus from the evidence (is) that climate change is exacerbating threats and risks to Australia's national security".

"These include sea level rise, bushfires, droughts, extreme rainfall events, and higher-intensity cyclones".

Leading aircraftman Aaron Townsend carries supplies to be flown to the Philippines for the Typhoon Haiyan relief effort. ( Supplied: Glen McCarthy/ADF )

Currently serving senior defence figures in Australia rarely speak publicly about climate security.

"To do that would necessarily mean putting your head above the parapet, so to speak," said Associate Professor Matt McDonald from the University of Queensland.

"That's where I think there is a concern — that you don't want to be engaging in what is a toxic politics around climate change in Australia."

Admiral, Home Affairs see climate change as common threat

Contributing to the enquiry was the former head of the Australian Defence Force, Admiral Chris Barrie.

Admiral (ret.) Chris Barrie has raised the impact of a future threat of a Cape Town-style water crisis right across Asia. ( ABC News )

When he was the Defence chief, it was his job to perceive future threats to Australia.

Now retired, the Admiral worries that climate change could cause huge security issues for the nation and no longer bound by office he is free to speak his mind.

Admiral Barrie has posed the scenario of what would happen if a Cape Town-style water crisis hit right across Asia, driven by receding glaciers in the Himalayan mountains.

"I'm talking China, around the Mekong river into Burma, Bangladesh, India, Pakistan. What will billions of people be doing about that problem?" he said.

"Well, one of the scenarios of course is, I think, they'll be looking for a new home."

The former Department of Immigration and Border Protection, now called Home Affairs, has also followed the logic of threat multiplication in its Senate enquiry submission.

"Climate change is likely to exacerbate the complexity and unpredictability of existing migratory pressures around the world and for Australia," it wrote.

"In most cases, climate change-related migration will not eventuate as straightforward cause and effect, but will be shaped by the interaction of climate change with cultural, economic and political processes."

Environment's 'threat multiplier' gets on Defence radar

Military interest in the consequences of climate change can be traced back to a landmark report commissioned by the US Department of Defense in 2007.

The report, National Security and the Threat of Climate Change, was overseen by Sherri Goodman, a former deputy undersecretary of Defense.

She assembled a military advisory board of twenty retired admirals and generals who concluded that "projected climate change poses a serious threat to America's national security".

In contrast to the science, Donald Trump has said climate change was created by and for the Chinese in order to make US manufacturing uncompetitive. ( Reuters: Carlos Barria, file photo )

Ms Goodman coined the term "threat multiplier" — meaning climate change may exacerbate existing threats rather than be a threat unto itself.

She reprised her 2007 message in a submission to Australia's recent Senate enquiry, advising Government to "recognise climate change as a global existential risk, and a direct threat to the national security of Australia".

The term and the ideas in the report had already caught on in Washington.

The Trump administration's current US Defense Secretary, General James 'Mad Dog' Mattis, at his confirmation hearing, seemed out of lock step with his soon-to-be commander-in-chief, stating:

"Climate change can be a driver of instability and the Department of Defense must pay attention to potential adverse impacts generated by this phenomenon."

Mr Trump has previously said the concept of climate change was created by and for the Chinese in order to make US manufacturing uncompetitive.

Study reinforces regional climate issues

A new study led by Australian scientist Dr Andrew King from the University of Melbourne paints a stark picture of this interaction between climate change and economics among Australia's neighbours in the Asia-Pacific region.

A map produced for the paper titled The Inequality of Climate Change from 1.5 deg C to 2 deg C of Global Warming shows a sea of red to Australia's north.

It indicates that poorer, tropical countries from India to Melanesia will notice a disproportionate amount of abnormal heat as temperatures increase by more than 1.5 degrees Celsius.

Dr King's research shows poorer, tropical regions will be disproportionally affected by climate change. ( Supplied: Andrew King/University of Melbourne )

Comparatively wealthy Australia on the other hand is predicted to be once again the lucky country.

Increases in temperatures here would not be as noticeable.

"We're using a quantitative measure of local climate change and then overlaying that with population data and GDP data," Dr King said.

"What we're really showing, and this does compliment what studies have shown before, that it's the poorest who will be worst affected by climate change."