@Kashishh: 'much' is used to describe extent, intensity, or degree. It is used to modify non-countables.
1. However much he loved her, she always pulled away.
2. Much of his hostility can be attributed to his lack of friends.
In both cases, you cannot count the thing that is being modified by 'much.' 'Love' and 'hostility' therefore are non-countables. Similarly, 'agree' is not something that can be counted. "Much of scientists' agreement on plate tectonics is actually based on shaky ground (so to speak

).
With 'many', the shift becomes one from non-countables to countables.
1. Many of his friends attest to his grumpiness.
2. Many of the country's economic woes can be attributed to bureaucratic ineptitude.
In both cases, the nouns - 'friends' and 'woes' can be counted.
Thus in the original sentence, we are modifying the extent of the scientists' agreeing, so we want to use 'much.'
Hope that helps