An introduction

The Earth's climate changes. In its ~4.5 billion years, our planet has been covered in ice during Snowball Earth events more than half a billion years ago and it has been warmer than present day during the Pliocene, just to mention a couple examples.  
So, if our climate has changed so much before we even existed, why would we think that us, puny humans, are capable of causing increased average temperatures, melting of glaciers, rise of sea levels? How are we even sure it is not just natural variability, or caused by external factors? And most importantly, is everything going to freeze over the day after tomorrow? (Probably not).
I will be looking into different periods in the Earth's past and present to try to understand if we really could be behind all that is happening today. After all, the climate is changing, right?

http://xkcd.com/1321/