You mean the climate can change without humans being responsible?
Who can imagine such a thing? /sarcasm
I've linked to a Scientific American article on Snowball Earth several times since it was published 4 years ago. It just goes to show that climate change has been going on throughout the Earth's history, including now. The Earth has undergone many global cooling and warming cycles throughout geologic time.
Why should anyone be surprised that we are apparently undergoing another bout of warming? Why should they automatically believe that human activities must be the cause?