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In this week's episode of Frontiers, Peter Evans meets climatologist Professor Bill Ruddiman whose views about climate change have divided scientific opinion.

Bill's argument is that 8000 years ago, Neolithic farming produced major emissions of carbon dioxide and methane. Land clearance and rice cultivation led to such large amounts of carbon dioxide and methane being released into the atmosphere that they countered the natural decreases that would otherwise have happened. Controversially, Bill suggests that these emissions averted natural global cooling and prevented an Ice Age in the northern hemisphere. Bill's hypothesis relies on climate information gleaned from ice deposits in and around Lake Vostok. He argues that if we compare our own interglacial period with similar periods up to 800,000 years ago, we find that carbon dioxide and methane trends in the late-Holocene were rising when they should have been falling. Bill suggests that these anomalous rises can only be explained by man's farming activities.

Bill was a delegate at the recent European Geosciences Union held in Vienna. He gave a paper entitled: 'The Early Anthropogenic Hypothesis - Challenges and Responses', which was criticised by many climatologists. Some of them voice their objections in the programme. Bill has recently lowered his estimate of the amount of carbon dioxide and methane produced by Neolithic man. However, his basic position - that man has affected the earth's climate for thousands of years - remains unchanged.