To what extent is climate change caused by human activity?

Palaeoclimatic records have allowed scientists to determine that the last 2 million years climate has fluctuated between periods of warmth and cold. Global average surface temperatures have fluctuated by as much as 5C between the two climatic regimes. In the longer term i.e. the last 50 million years the Earth has become much colder. The size of the ice caps has repeatedly grown and shrunk every 100,000 years. (Figures UNFCCC 2001). At present we may be coming towards the end of the latest warmer interglacial period, although mankind’s alteration of the atmosphere through greenhouse gas pollution makes predicting the long term future of our global climate difficult….(short extract)