Global warming natural or man-made?

Learning about the Earth's past it is evident that there have been periods of very cold temperatures called 'Snowball Earth' followed by very hot temperatures, which have a causal relation with one another. When we talk about current 'Global Warming' a lot of scientists are of the opinion that it may be a natural phenomenon and not an outcome of some particular human activity which is causing it. Nevertheless, there are evidences to make us realize that it is more due to 'Greenhouse Effect' than the natural causes. 

Human activity on earth is inevitable for the survival of our race. In turn,it causes the forest to be replaced by towns and cultivated land. It causes the rivers and streams to be loaded with chemicals toxic for water ecosystems. It causes habitat and species endangerment leading to extinction in some cases, and most of all, our atmosphere which is a protective blanket of air above us, crucial to our existence, is getting affected. The picture and the link below will explain more how our environment is changing.    

http://www.skepticalscience.com/10-Indicators-of-a-Human-Fingerprint-on-Climate-Change.html