I've read about snowball earth. It was about 600 million years ago and the most severe ice age the earth ever had. They think the earth was completely encapsulated in ice all the way down to the equator.

I've listened to interviews on YouTube of Robert Felix and John Casey. They are both scientists who think the earth is cooling. The interviews are very interesting and give a perspective that is never presented in mainstream media.

This is Robert Felix's website. Some pretty interesting stuff.  
iceagenow.info