Karpas symbolizes springtime and the miracle of nature's renewal. 
Yehudis Cohen wrote this poem while in Israel:

The blue, blue sky was filled with
billowy, pillowy, cottony cloud- and
so too were filled the dreams of all 
who stood there. 

And the green spring grass, dancing
in the soft wind, called all to listen 
to the declaration of the passing of
winter and to bring hope that new life
would soon appear. 

haggadah Section: Karpas