Will Saunders, a British astronomer at the Anglo-Australian Observatory in Sydney, left the world in no doubt as to his feelings about the current situation in Iraq. He is one of two protesters arrested for daubing “No war” in huge red letters on the roof of Sydney Opera House (see page 366). In January, 41 Nobel laureates chose a more conventional means of making a similar point, declaring that an attack on Iraq without widespread international support “would undermine, not protect, US security and standing in the world”.

Within the broad church of the scientific community, however, there will be those who believe, with equal sincerity, that war is justified to rid the world of a regime that has repeatedly attacked its neighbours and used chemical weapons against its own people. Public statements by pro-war scientists are difficult to find, but some researchers will privately feel that the real villains of the piece are those nations that refused to lend international legitimacy to military intervention. Other scientists will be watching the hostilities unfold in unprecedented detail on their televisions, unsure what to make of it all.

Given this spectrum of opinion, bodies that represent researchers have mostly been silent, realizing that there is no single 'scientific' perspective. Nonetheless, the scientific community should recognize that it has some particular responsibilities, and a huge stake in rebuilding an international consensus. Scientists, after all, helped to develop both the high-tech armaments being used to pursue the assault on Iraq, and the weapons of mass destruction whose alleged possession by Saddam Hussein paved the road to conflict in the first place. Scientists will also play a leading role in verifying claims by the combatants about both types of weapon (see pages 362–363).

More fundamentally, science owes its rapid advancement to the free exchange of ideas and personnel between labs across the globe. Security restrictions introduced by the US administration as part of its 'war on terror' are already impeding this exchange (see Nature, 422, 96–97; 2003). If the situation is not now to deteriorate further, scientists must speak out, both to protect progress in their own disciplines and to defend a plethora of international agreements thrashed out under the auspices of the United Nations. The Kyoto Protocol on climate change, the Convention on Biological Diversity, the Chemical Weapons Convention, the Nuclear Non-Proliferation Treaty and others all owe their existence, at least in part, to international scientific collaboration.

The world has much to lose if the current conflict leaves this legal framework, like central Baghdad, in smouldering ruins. Even before the Iraqi crisis came to a head, President George W. Bush's administration had shown itself to be no lover of international agreements. Now, having split so acrimoniously from many of its traditional allies, there is a danger that the world's only superpower may decide that there is little to be gained by working with the United Nations. And that could, in turn, give rise to a highly dangerous situation in which nations and religious factions jostle freely in pursuit of their own interests.

Instead, we must hope that an international consensus can be rebuilt, if falteringly at first. Scientific organizations have not had much to contribute to the debate running up to this war. But in its aftermath, they should speak up loud and clear to press for internationalism in a world that could otherwise veer towards factionalism and further conflict.