When the world's scientists emerge from their labs and take to the streets there must be something very important at stake. For the most part, scientists are most unlikely activists and public figures. We've been explicitly taught, perhaps erroneously, that our profession is above politics. Yet, an unprecedented series of "marches for science" through major cities across the globe in April will bring leading scientists, including Nobel Laureates, together around both a political, and a more fundamental, challenge.

On the face of it, the planned marches, including those in Sydney, Canberra and Melbourne, are a protest against US President Donald Trump's anti-science stance on critical global issues, such as the irrefutable contribution of human activity to climate change, and his steady stream of "alternative facts".

But, there's something bigger in play. That is, the rise of a wider "post-truth" political culture in which opinion and ideology are overriding facts, and in which populism, not a credible evidence base, is informing policy-making – well beyond the new US administration. As such, we scientists find ourselves with an unfamiliar, even uncomfortable, role to play in the public arena.

But, why march in defence of a method? Science is not the only lens through which we can understand the world, nor is the scientific method immune from challenge.