First of all, asteroids aren’t caused by global warming. They’re the floor sweepings left over from the formation of the planets billions of years ago. Some of them are pretty big. Indeed, one of them, Ceres, is large enough to qualify as a dwarf planet. Most of them are tiny.
Several tons worth of the tiny asteroids collide with the Earth each day. Almost all of them burn up in the atmosphere as meteors. A few make it to the ground as meteorites. Every thousand years or so, a large meteor weighing tens of tons smacks into the ground releasing energy equivalent to a nuclear weapon. This happened in Siberia in 1908. Larger, Earth-shattering kabooms occur every few million years when an asteroid several hundred metres (or larger) in diameter hits. A large strike about 66 million years ago ended the Age of Dinosaurs.
This Friday’s asteroid will miss us. If it were to hit, the energy release would be roughly equivalent to a 2 megaton nuke, inconvenient for the local neighborhood but hardly Earth-shattering.