18 For the wrath of God is revealed from heaven against all ungodliness and unrighteousness of men, who hold the truth in unrighteousness; 19 Because that which may be known of God is manifest in them; for God hath shewed it unto them. 20 For the invisible things of him from the creation of the world are clearly seen, being understood by the things that are made, even his eternal power and Godhead; so that they are without excuse: 21 Because that, when they knew God, they glorified him not as God, neither were thankful; but became vain in their imaginations, and their foolish heart was darkened. 22 Professing themselves to be wise, they became fools, 23 And changed the glory of the uncorruptible God into an image made like to corruptible man, and to birds, and fourfooted beasts, and creeping things. 24 Wherefore God also gave them up to uncleanness through the lusts of their own hearts, to dishonour their own bodies between themselves: 25 Who changed the truth of God into a lie, and worshipped and served the creature more than the Creator, who is blessed for ever. Amen. 26 For this cause God gave them up unto vile affections: for even their women did change the natural use into that which is against nature: 27 And likewise also the men, leaving the natural use of the woman, burned in their lust one toward another; men with men working that which is unseemly, and receiving in themselves that recompence of their error which was meet. 28 And even as they did not like to retain God in their knowledge, God gave them over to a reprobate mind, to do those things which are not convenient; 29 Being filled with all unrighteousness, fornication, wickedness, covetousness, maliciousness; full of envy, murder, debate, deceit, malignity; whisperers, 30 Backbiters, haters of God, despiteful, proud, boasters, inventors of evil things, disobedient to parents, 31 Without understanding, covenantbreakers, without natural affection, implacable, unmerciful: 32 Who knowing the judgment of God, that they which commit such things are worthy of death, not only do the same, but have pleasure in them that do them. ~Romans 1:18-32
According to verses 19 and 20, who knows God exists? That’s right, everybody. So, on the basis of the Word of God, there are no atheists; there are only people who suppress the truth that they know about God in their unrighteousness. In other words, they don’t want God to exist so they can live however they wish.
The following from Voddie Baucham will help frame our discussion.
“Three phrases in this paragraph support Paul’s conclusion that people are “without excuse” in terms of general revelation. First, the phrase, “is plain to them,” reminds us that the knowledge of God we receive from general revelation does not require unusual effort. The second phrase, “God has shown it to them,” reminds us that general revelation is not hidden or secret. The third phrase, “have been clearly perceived,” reminds us that general revelation (Rom. 1:18-31) cannot be missed by accident. Doing so requires suppression.
Put these three together and we see that God has provided a means of knowing about him that requires no special effort, is not hidden, and cannot be missed unless, of course, we want to miss it. And that is why those who “miss it” are said to be “without excuse.” Thus, the spiral begins when men reject God’s general revelation. Consequently, they continue downward and refuse to honor the God they know.” 
Many professing atheists will say there is not enough evidence to conclude the existence of God, or that God has not proven Himself to them. But the Bible says there is more than enough evidence to prove God’s existence (again, see vs. 19-20). He has demonstrated Himself through creation and the conscience. The problem is not a lack of evidence, but an unwillingness to believe. Notice the underlined portions and see that professing atheists willfully reject the truth they know about God and will therefore experience God’s judgment unless they repent. Moreover, they hate God (v. 30). They may deny it, but it’s true. Many professing atheists are “former”  Christians and began to profess atheism either after a tragedy they experienced, or in rebellion against their parents/the Church. This is evidence of their hatred toward God.
Many professing atheists say, “If God were to show me a sign, I would believe.” However, that is also false. Many people saw the signs, wonders, and miracles Jesus performed while He walked the earth, yet not everyone believed on Him.  This is further support for my claim that it’s not a problem of evidence for the supposed atheist. It’s merely a ploy to mask their unwillingness to believe.  If God showed them a sign, they would find a way to explain it away. Because they don’t want to acknowledge and submit to the God they know exists.
Incidentally, verses 19-20 also answer another common question. That is, what of the person deep in the jungle who has never heard of the Name of Jesus? Will God send them to hell, holding them accountable for what they don’t know? This is usually brought up by unbelievers in the context of questioning God’s justice. As if God would be unjust if He were to send them to hell. But according to these verses, we see God’s revelation is universal in creation; God has revealed Himself to everybody everywhere. While this revelation is not enough to save anyone, it is enough to damn them, “so that they are without excuse.” So God would be just in condemning them if they don’t acknowledge God’s revelation in creation. If, however, they go the opposite direction of the downward spiral seen in verses 21-32 and acknowledge God, then God will providentially get the Gospel to them. Moreover, as the Apostle Paul goes on to elaborate in this letter to the Romans, everybody is under sin. Therefore, God would be just in condemning them to hell, whether they heard the Gospel or not. But let’s delve deeper, and see if that’s what God will do.
In His Olivet Discourse, Jesus said, “And this gospel of the kingdom shall be preached in all the world for a witness unto all nations; and then shall the end come,”  in answering His disciples’ questions about the end of the age. In other words, Jesus will not come back until everyone has heard the Gospel. Whether from a person, or even an angel,  everyone will have the Gospel preached to them; no one will be able to say they didn’t know, or had never heard. How do I know Jesus’ words apply to everyone – that everyone will hear the Gospel? Revelation 5:9 records a song sung by those who are “redeemed…out of every kindred, and tongue, and people, and nation.” People from every clan, language, people group and ethnicity will be in heaven, so God obviously gets the Gospel to them, and some of them believe. Rather than smear God for not saving everybody, let’s praise Him for saving anybody!
So, while progressing atheists claim to not believe in the existence of God, God says in His Word that atheists don’t exist. “Let God be true, but every man a liar.”  Hence, Christian, next time you are in a discussion with someone and they claim to be an atheist, don’t believe them.
 Voddie Baucham, Expository Apologetics, p. 51, italics in original
 1 John 2:19 clearly states that there is no such thing as a “former” Christian. If they professed faith and no longer hold to that profession, then they never truly believed.
 His own disciples didn’t even believe He rose from the dead when He was standing right in front of them!
 They also have an inability to believe, since Ephesians 2:8 says faith is granted as a gift from God.
 Matthew 24:13-14
 See Revelation 14:6-7
 Romans 3:4