Science says there is no God

Some people say that science says there is no God
how does one respond?

We should respond lovingly, carefully and prayerfully. First it should be remembered that many scientists have stated that science has drawn them closer to God. As they see the order, the magnitude, and the diversity of creation they cannot help but to see there is a God.
The Catholic Church teaches that inherently people search for God.

“The desire for God is written in the human heart, because man is created by God and for God; and God never ceases to draw man to himself. Only in God will he find the truth and happiness he never stops searching for:

The dignity of man rests above all on the fact that he is called to communion with God. This invitation to converse with God is addressed to man as soon as he comes into being. For if man exists it is because God has created him through love, and through love continues to hold him in existence. He cannot live fully according to truth unless he freely acknowledges that love and entrusts himself to his creator.[1] CCC#27
This search for God leads to the various responses and expressions that we see today. Some, unfortunately, reject a relationship with God with a decision they make. Atheism is from our perspective a relatively recent invention flowing from the enlightenment.
But this “intimate and vital bond of man to God” (GS 19 # 1) can be forgotten, overlooked, or even explicitly rejected by man.[3] Such attitudes can have different causes: revolt against evil in the world; religious ignorance or indifference; the cares and riches of this world; the scandal of bad example on the part of believers; currents of thought hostile to religion; finally, that attitude of sinful man which makes him hide from God out of fear and flee his call.[4] CCC#29

As one can see, there are many reasons why a person could reject the idea of a God. This is where we should respond as I stated above — lovingly, carefully and prayerfully, as we share our own experiences of God with those who find it difficult to believe.