Global warming is a big thing to worry about, but for a long time people didn't believe it was happening or that is was caused by people.

There is now lots of evidence that it is caused by humans and is affecting people right now.

This house is falling down because the frozen earth that it stood on has now melted. 

Al Gore, who was vice President of the United States, made a film called An Inconvenient Truth all about global warming. This is the trailer.