CANBERRA – Despite the United Nations Security Council’s belated endorsement of UN Special Envoy Kofi Annan’s peacemaking mission in Syria, confidence that Syrian President Bashar al-Assad will cooperate in any serious or sustained way remains low, and calls for external military intervention continue.

As Syria’s crisis goes from bad to worse, those urging armed force are invoking both the tragedy of inaction in Rwanda and Bosnia in the 1990’s, and the triumph of decisive international action in Libya last year. The proposals run the spectrum, from establishing no-fly zones, buffer zones, "no-kill zones,” safe-havens, and protected humanitarian corridors to arming the Free Syrian Army to fight Assad’s regime. Still others urge outright invasion to overthrow it. The agonizing question for those who believe that the international community has a responsibility to stop mass-atrocity crimes is not only whether any of these options is practically achievable, but also whether they will do more good than harm.No military option currently has any chance of support from a UN Security Council that is still largely paralyzed by a backlash against NATO’s perceived overreach of its civilian-protection mandate in Libya. The only military option that has received any practical international backing so far – reportedly from some of Syria’s Sunni Gulf neighbors – is the arming of opposition forces.That said, if some form of coercive military intervention is the right course to take in Syria, the argument should be made with passion and persistence. But is this a case in which it is right to fight? Under the responsibility to protect (R2P) principles that the UN General Assembly unanimously endorsed in 2005, coercive military action to stop atrocities should be contemplated only when peaceful means – from diplomatic persuasion to sanctions and threats of criminal prosecution – prove inadequate. Clearly the situation in Syria has reached that threshold.But contemplating military action does not mean endorsing it. Both morality and prudence demand that several criteria be satisfied before any use of force is approved. No such guidelines have yet been formally adopted by the Security Council or the General Assembly, but five criteria have emerged from the R2P debate over the last decade.The first criterion is the potential harm to civilians: is the threat of a type and scale that prima facie justifies the use of force? With more than 9,000 people already dead in Syria and the toll rising daily, this criterion certainly seems to have been satisfied, although the violence is no longer as one-sided as it was at the outset.The second test, more subjective and tricky to apply – and therefore not decisive in itself – is whether the primary purpose of any proposed military action is to halt or avert the threat to civilians. Some Gulf countries’ enthusiastic support for intervention in Syria may well be driven primarily by another agenda: anti-Iranian and pro-Sunni sentiment.Third, there is the issue of last resort: has every non-military option been explored and found unlikely to succeed? The jury is out on this, but may not be for much longer. For all of the hopes, there are no high expectations that Annan’s negotiation skills will, even now with Security Council support, succeed in defusing the Syrian crisis, as they did following Kenya’s explosive presidential election in 2008. And few are confident that even universal sanctions or other non-military pressure will stem Assad’s determination to crush his opponents.The fourth criterion concerns proportional means: are the scale, duration, and intensity of the proposed military action the minimum necessary to meet the threat in question? This was one of the most controversial aspects of the intervention in Libya. The trouble with most of the proposed "minimalist” intervention solutions – establishing buffer zones, for example – is that, in Syrian conditions, full-scale warfare will almost certainly be required to impose them. The minimum may have to be the maximum.The final, and ultimately the most crucial, criterion for intervention is the balance of consequences: will military intervention do more harm than good? This is where the argument in favor of military intervention in Syria runs into the most trouble.Any further militarization in Syria runs the risk of turning what is already a nascent civil war into a full-blown one, with casualties on a much greater scale. The Syrian military and government-backed militias are strong and will resist fiercely. Sectarian differences within Syria are profound, and there is little international confidence in either the cohesion or the democratic and human-rights credentials of the opposition. Fighting there could ignite the entire region. And, with the Arab League divided over the issue, any Western intervention is bound to be inflammatory in the wider Islamic world.With all military options appearing to be counterproductive, the only chance of halting Syria’s descent into total chaos is Annan’s political mediation. Its unstated premise is that enough senior officials in the regime can be persuaded to change course, with enough safe exits for the most divisive figures, to enable the situation to stabilize and reform to start. But, for that to happen, Russia will have to exercise its influence much more constructively than it has so far. That is a slim reed for the Syrian people to grasp, but unhappily it’s the only one around.Gareth Evans, Australia’s foreign minister for eight years and President and Chief Executive of the International Crisis Group from 2000-2009, is currently Chancellor of the Australian National UniversityCopyright: Project Syndicate