Revelation 8:7

7 The first angel sounded, and there followed hail and fire mingled with blood, and they were cast upon the earth: and the third part of trees was burnt up, and all green grass was burnt up.

This is the first of seven trumpet judgments. The last three trumpets are also called woes with the last woe containing the seven vials of wrath from God. This first trumpet sounds and fire and brimstone are cast onto the earth. One third of the trees on earth are burned up and all green grass.

This is not nuclear warfare as some have suggested. I believe what will take place from a natural point of view in these judgments is the result of a great comet that is advancing on the earth after it travels around the sun. I think angels at times use what appears as natural events to the world to fulfill the supernatural will of God. A decade or so ago we saw a multi-headed comet hit Jupiter over a period of days. If it had hit the earth, its effects would have been just as catastrophic as what we will see in these judgments. Some of these events will be very similar to what was experienced in the plagues of Egypt but now it will be over one third of the earth's surface. As the great comet approaches the earth, the earth is first impacted by the tail and great flaming balls of fire rain upon the earth and cause this disaster by fire.