How is an online article referenced if there is no obvious author?

There are probably several answers depending on the situation and on the standards in your field.

First there are papers published in journals with no authors that are referenced as:

Anonymous, yyyy. Paper title ...

In some cases an organization can be the author. this is true for, for example, governmental organizations, NGO's etc. In these cases the publications are offically published. References would be listed under the organization (often abbreviated) such as:

WMO (World Meteorological Organization), yyyy. Publication title ...

To reference online material is always a bit more complicated but I guess the anonymous author can be used and the source organization listed as the "Publisher" such as the The Guardian in your example. The point is that the source is known but not the author. If you have a lot of these sources there will of course be many "anomymous" floating around in th etext and reference list which may be awkward. In such a case you may consider using the organization as author.