verbs - "were" instead of "was"

“We’re just happy our little girl is alive,” said Jessica’s father, Michael Paulsen, as though the state of being alive were itself a sufficient cause for happiness and not a prison of its own, at least in a phenomenological sense

I read this paragraph on the Onion News. I wonder, why were is used as the linking verb instead of was in the part of the sentence "... as though the state of being alive were itself a sufficient cause for..." ?