Phileas Fogg and Gulfstreamaviator, my last post about lengthening the existing runway was to illustrate the madness to even concider do so.
I think it also was suggested to lengthen the runway to the south in to the sea, but then you have to struggle with water depths of more than 40 metres. The costs will be big, both for the purse and nature.
The last point this time: The aircraft types used today are among the noisiest used for passenger traffic today. With so few on board each aircraft, the exposure (the number of flights) is also very high. In other words, any change will reduce the noise levels.