"Why is that?" Every take off must be performed at a higher power setting. Therefore increasing fuel burn, pollution and engine maintenance cost and larger noise footprint
Actually, the others are correct, lower thrust setting is lower temp and increased pollutants. This is why idle thrust creating less pollutants on ARR is a myth. (and why one does not see it advertised as a benefit for RNP-AR)
Increased fuel burn.... given the duration of thrust, and the altitude difference, I would not say that.
Increased noise footprint, yes a little, but duration is less, so the resultant exposure footprint is less with higher thrust setting due to the altitude difference.
the best scenario is to jump up quick and level off getting clean...more initial noise, but smaller exposure footprint, with better fuel burn (less pollutants)