What do you think it takes to convince an atheist that God exists

When I consult with my friends who are atheist, I often ask them why they came to that decision. Their answers tend to fit into three categorical responses:

1. I have problems believing the accounts in the Bible are factual (i.e. the creation of the world in six days, man's creation only 6,600 years ago, "human" remains that are older than what the Bible says is possible, et al.);

2. A loving and just God (as described in the Abrahamic faiths) would never allow this much violence, hate, oppression and indiscriminate suffering in the world to persist, nor would God allow religious persecution of those who follow His ways; 

3. Science has already disproven God's existence and evoltution is the true progentitor of all life. 

I would really like to know what Big Think users believe it would take to convince someone who is an atheist that God exists. If you are an atheist, what do you think it would take to convice you? Finally, if you are an atheist, how certain are you that there is no God?