Noah and his family left the Ark and offered sacrifices to Hashem. In 8:21 the Torah tells us that Hashem smelled the pleasant smell (of the korban) and said to Himself He would no longer curse the land because of man.." "וַיָּרַח יְהוָה, אֶת-רֵיחַ הַנִּיחֹחַ, וַיֹּאמֶר יְהוָה אֶל-לִבּוֹ לֹא-אֹסִף לְקַלֵּל עוֹד אֶת-הָאֲדָמָה בַּעֲבוּר הָאָדָם".
The smell of meat pacified Hashem and made Him change His position on the idea of wiping out mankind? It is not like the korbanot Noah brought were a surprise and He saw the goodness of Noah that caused Him to change His mind - Noah knew (in 8:20;Rashi) that Hashem told him to bring 7 of each kosher animal specifically for the purpose of having animals for korbanot - so Hashem knew and really in essence told Noah to bring the korbanot.
So why did He change His attitude?
When the smell reached Hashem he recognized that Noah really did have the best intentions and despite the fact that man is evil from his youth (the continuation of the passuk), there is potential for good and even for greatness. That being the case, there is hope for mankind. That is what pacified Hashem. The smell of the korban caused Hashem to realize (k'v'yachol) that there is great potential in man and therefore should not be destroyed.