On Friday November 6th there was an asteroid near miss. This was a small asteroid that came within 14,000km of Earth. It was only spotted a short time before it made its pass at Earth.
Asteroids of a certain size could cause real problems for we Earthlings. Much bigger issue than global warming. There are people scanning the skys for Asteroids. When one is found, calculations are made to determine if they present a real danger —(I am not very confident that we are prepared to deflect the body away from Earth if it were a danger). You might be interested in some observations about the most recent miss, and a longer ranged view of the consequences of a strike.
If so, look at this one for comments about the Nov. 6th asteroid here.
This site charts the close ones every day, click here and page down to near the bottom of the site to see Near-Earth Asteroids.
And click here for a site that give some history and a cool video of the consequences of a major asteroid strike