In Khan Sheikhoun, a rebel held town, there have been reports of a chemical attack. The reports claim that it were launched by the Syrian government.
According to the Chemical Weapons Convention the use of chemical weapons has been outlawed internationally.
If it would be proven that a chemical attack was indeed launched by the Syrian government, what could the United Nations do?
Wag their fingers.
Russia has released a statement that supports the government's stance that it did not use chemical weapons. This probably means Russia would not support any UN intervention, and as a veto country they have the power to prevent the UN from doing anything meaningful.
The OPWC is a separate treaty organization from the UN responsible for chemical weapons but it seems to have little or no direct power. It can investigate and point fingers, which may be embarrassing.
The general assembly of the United Nations could pass a resolution condemning the attack. In the past, it has passed for example Resolution 47/121 condemning ethnic cleansing of the Bosnian Muslims by the Bosnian Serbs. Such resolutions can be passed by a simple majority, or a two thirds majority if the issue is considered important. General assembly resolution by themselves do however rarely translate in to impactful actions, such as military interventions.
More effectual resolutions can be passed by the United Nations Security Council. Such resolutions have in the past lead directly to military interventions, for example Resolution 743, leading to the establishment of a peacekeeping mission in Yugoslavia under a UN banner, and Resolution 1973, leading to military intervention in Libya.
However, United Nations Security Council resolutions can be vetoed by any of the five permanent members of the Security Councils. In the case of Syria, the position of Russia as a permanent member would likely prevent any resolution that could be a grounds for anti-regime action, as Russia has vested interests in the continuation of the Assad regime.
If the attack was proven to be launched by the Syrian government, what could the United Nations do in Syria?
Regardless of who launched it, the approach would be the same: investigate the case, find the responsible party, build a coalition to punish it.
Assad is bad but not stupid. It would be irrational for him to do it now, given that he is having an upper hand in the fight, and the USA just backed down from insisting his removal as a pre requisite to the peace process there.
It almost sounded like some one is trying to derail a political solution there.
In theory they could authorize a full military intervention by member states, or send their own troops for a peacekeeping mission, or impose economic sanctions.
In practice, they will do none of that, because all of those actions require unanimous approval of the Security Council. Russia would certainly veto any such action against their only ally in the region, and China would likely do so as well (they typically have issues with the idea of the UN intervening against a UN-recognized government in a purely domestic issue). This veto from both parties has in fact already happened at least 7 and 6 times respectively.
So most likely none of those things will happen.
That only leaves toothless resolutions and condemnations as likely options. Those can be passed by simple majorities in the General Assembly. Doing so may hurt the prestige of Syria and the vetoing countries, but that's not an injury Security Council members have traditionally lost a lot of sleep over.
The UN can pass its time in doing noble things such as passing resolutions, sending representatives, and other forms of looking busy, but can do exactly nothing that really helps prevent or punish.
In geopolitics it is safe to assume that the human species is not a civilized one. It is not surprising therefore that the species currently does not possess the means or mechanisms to enforce civilized standards of warfare.
Nothing should be done to interrupt, slow, or postpone the war in Syria. Questions of right and wrong cannot be settled during a war but at most only after the war, and only in a symbolic way like the Nuremberg trials, and that too only if the Good Guys have won.
