According to the Medrash, when G-d states in the Chumash that "Man's years
will be 120" (B'reishis 6:3) it refers to the time granted for Humanity to
repent before the flood. During that time, Noach worked publically on the
ark and warned the people around him of the coming Mabul [flood]. There
was also a flood in the time of Enosh(the grandson of Adam) seven
generations earlier -- a warning ignored by this later generation.
Many meforshim [commentators] rate Noach as less than Avraham because he
just did as Hashem told him without actively trying to stop the flood (as
Avraham did with S'dom). Others state that Avraham could pray for S'dom
because they were an individual group of cities, while the rest of the
world had already moved beyond such a low level. In Noach's time, since
the entire world had collapsed, there was nothing further he could do.
Hillel (Sabba) Markowitz