The value of acceleration due to gravity considering the rotation of the earth is,
\[g’=g-\omega^2R\cos^2\theta\] where $\theta$ is the latitude of the given place.
[Variation of g due to the rotation of the earth]
If the rotating speed of earth increases, then $\omega$ will increase. So, the quantity $\omega^2R\cos^2\theta$ will go on increasing. Hence, the effective value of $g$ will decrease if speed of the earth increases.