>> how do we govern global issues without a global government?
By consensus. By willing participation of all. By individual countries actively deciding to operate in the agreed best interests of the whole. And when countries act egregiously badly, subsets of the larger group band together to employ military force against them. Government can exist without rigid structures. The enforcement of norms by the collective is a form of government. This is what they mean when diplomats speak of threats to the "international system" even though we lack any official world government.
Well, governments also can declare wars, send chaps off to die in them, and lock people in boxes for not following rules written down by the governments. They can also collect money from people under same threat of box-locking.
Not every "enforcement of norms by the collective" (what's the collective?) can do that.
A government by definition has a monopoly on state violence. If constituent members are going to war against each other then the so-called global government is not actually a government, it's more of a voluntary association similar to the UN that doesn't actually have much real power.
By consensus. By willing participation of all. By individual countries actively deciding to operate in the agreed best interests of the whole. And when countries act egregiously badly, subsets of the larger group band together to employ military force against them. Government can exist without rigid structures. The enforcement of norms by the collective is a form of government. This is what they mean when diplomats speak of threats to the "international system" even though we lack any official world government.