Surely vs certainly

Hi, everybody! Here are two sentences:

  1. I would [color=red]surely have noticed more if I had realized the importance of the sea to us human beings.
  2. New sources of energy can [color=red]certainly be obtained from the sea.
    It is said that each is appropriate for its sentence. But why? I’m not clear about their difference need your help.

Hi Daisy,

[color=blue]Surely in your sentence is used in a way to ask for confirmation: I would surely (wouldn’t I?) have noticed …

[color=red]Certainly in your sentence indicates that it’s clear/that it’s definite: can certainly (there is no doubt) be obtained …