The phrase "are surely complex" is correct and usable in written English.
You can use it when discussing something that is undoubtedly intricate or complicated.
Example: "The issues surrounding climate change are surely complex, involving numerous factors and stakeholders."
Alternatives: "are undoubtedly intricate" or "are certainly complicated."
While the ethical issues here are surely complex, we do not believe the work of the militarized anthropologists described in your article satisfies these requirements.
The reasons for that are surely complex, but it seems to come down to maturity of age and experience: some combination of a more developed sense of self, personal requirements for partnership, and the financial stability of a few years of work after school.
His impulses at Suez were surely complex.
The full story when it comes to online social media use is surely complex.
For African-Americans, the connection between beans and fortune is surely complex.
Whatever is going on, it is surely complex, for the ultraviolet spectra of the stars tend to vary with time, implying that the wind is not steady.
"Merz's metaphysic is surely complex and open-ended but clearly interested in large questions," Wilson wrote in his review.
A person's capacity for novel-writing and the kinds of thing a novelist writes are surely no more complex or mysterious than a tendency towards jealousy or a reluctance to hug one's siblings.
Other changes have occurred in relation to pregnancy and childbirth in Latin America which affect anthropometric measures in newborns, and are surely part of the complex mix in the Chilean situation as well.
Obviously, geopolitical considerations are complex, but there are surely other options than suspending arms sales, though such a move by the United States would doubtless be welcome in other parts of the Arab world.
A captain's task is surely more complex when leading so cosmopolitan a group.
