I remember when I pulled out one of my father's books as a child. It was by Albert Einstein. I could barely read then, but I began reading about the sun. Then I read something that spooked me. He said, "The sun is slowly, but surely, burning out." Even though my parents attempted by to sooth me by telling me it would be many millions of years before this happens, it still shook me. It disrupted my worldview of permanence.
Now I've become more religious and believe we're living in the last days prior to Christ's coming. Peter wrote: "Knowing this first, that there shall come in the last days scoffers, walking after their own lusts, and saying, Where is the promise of his coming? For since the fathers fell asleep, all things continue as they were from the beginning of the creation." (1 Peter 3:3-4)
When things begin in earnest, the religious people of the earth will see it as the work of God, who often works through natural events. Others will say that it's because of man's neglect of the earth that it's happening. Prophecy states the tribulations in the earth will fail to move many to repentence. Instead, they will "curse God and die."
The purpose of the tribulation is to assist in preparing the world for the Millennium by ridding the earth of the wicked. But there will be many good, decent, honorable unbelievers who will be spared. During the battle of Armageddon, when the Beast brings his army against Jerusalem, God will not destroy the entire army, but will leave a sixth of them. The warlord and his primary divisions, however, will be destroyed by the "brightness," or glory of the Lord's coming. In other words, no man can see God and live without the protection of the Spirit of God. The honorable men of the earth will be spared, whether atheists or agnostics. Even some Unitarians will be spared! :^)