cipher - An Unfortunate Conundrum Involving Extremes

The tide recedes as I sit in the fenced garden on my roof. A jagged rock lies ready to wreck the mariner who errs. A seabird screeches somewhere to my rear. Longing, I look at the world beyond the rail. The earth is green. It is the middle of the day and I am listening to Abba. A beat of wings and the bird comes in sight - nature and I are in sync. He who renounces nature, wherever he may roam, goes nowhere.

What is my number?

Hint 1

Throw up your hands in surrender: this is one of the harder ones.

Answer

Your number is:

Thirteen.

Why?

The last word in each sentence can be transformed with Rot13 to give another English word. That word is described at the beginning of the sentence:

The tide recedes as I sit in the fenced garden on my roof — ebbs.
A jagged rock lies ready to wreck the mariner who errs — reef.
A seabird screeches somewhere to my rear — erne.
Longing, I look at the world beyond the rail — envy.
The earth is green — terra.
It is the middle of the day and I am listening to Abba — Noon.
A beat of wings and the bird comes in sight - nature and I are in sync — flap.

He who renounces nature, wherever he may roam, goes nowhere — abjurer.

Throw up your hands in surrender: this is one of the harder ones — barf.

Unfortunalely, I haven't got any good explanation for the title.