This group is loosely defined, but it is set apart by its "silent" nature. MPs have since taken to valorising such quietness in public debate.

When a group of protesters took to the streets last month to voice their views about climate change action, they were swiftly chided for not staying at work.

Children were encouraged to go to school instead. Be quiet, and get on with things, all were told.

Public servants are arguably among the quietest Australians of all, in their private lives at least. Any bureaucrat considering joining in the climate strike had to weigh up the risks it would pose to their job.

Finance Minister Mathias Cormann spoke in veiled terms to discourage them from hitting the streets, saying they knew what their "duties and responsibilities" were. Restrictions on public servant free speech remain unclear and blow a chill wind through the federal bureaucracy.

Public servants must be part of the majority of Australians who are worried about climate change, as measured in a recent Australia Institute survey.

Despite being some of the most qualified people to speak about it, their nation is unlikely to hear much from them. That's a shame.

How much of a shame? Well, 16-year-old climate change activist Greta Thunberg's landmark speech to the United Nations gives an idea.

She reminded anyone listening that the science is clear, options to stem the worst are rapidly shrinking, and the solutions governments are offering simply aren't on track to avert unacceptable temperature rises.

The burden of consequences grows larger the younger you are. No surprise that children are skipping school, and a teenager is addressing a room full of adults at the UN, to point this out.

While some are getting loud about climate action, bureaucrats are indeed getting on with things and doing their jobs.

They're quietly preparing for climate change.

A speech written for Australian Defence Force chief Angus Campbell shows the military expects the fallout from rising temperatures could stretch its capabilities in coming years.

A series of documents also shows the public service's most senior leaders have met and "war-gamed" government responses to climate change scenarios.

Public servants evidently think differently to their own government about climate change. This creates a moral conundrum for them, where their responsibilities as professionals and human beings clash or converge.

To what extent do they voice their views on climate change, to their ministers, internally to their agencies, or externally? How do they advise a government that sees the problem in different terms?

Or should they simply be executors of the government's agenda, as Prime Minister Scott Morrison has told them?

The climate change challenge shows that the public service's role is larger than this. The bureaucracy predicts, plans for and advises governments on emerging threats, security or economic. Climate change is no different.

History shows that crises eventually focus the minds of nations, a collective survival instinct kicks in and the people chuck out those not up to leading them through the challenges.

Those leaders that have been up to such jobs have relied on a well-equipped, expert public service.

Climate change, like previous threats to the nation, will make an asset of the federal bureaucracy.

It is already quietly embracing its role.