William Ruddiman

[1] Ruddiman is best known for his 'early anthropocene' hypothesis (or 'Ruddiman hypothesis'), the idea that human-induced changes in greenhouse gases did not begin in the eighteenth century with advent of coal-burning factories and power plants of the industrial era but date back to 8,000 years ago, triggered by the intense farming activities of our early agrarian ancestors.

[2] It was at that time that atmospheric greenhouse gas concentrations stopped following the periodic pattern of rises and falls that had accurately characterized their past long-term behavior, a pattern which is well explained by natural variations in the Earth's orbit known as Milankovitch cycles.

The overdue-glaciation hypothesis has been challenged on the grounds that alternative explanations are sufficient to account for the current warm anomaly without recourse to human activity, but Ruddiman challenges the methodology of his critics (see external links).

Ruddiman is also known for his hypothesis in the 1980s that the tectonic uplift of Tibet created the highly seasonal monsoonal circulation that dominates Asia today.

With his then graduate student Maureen Raymo he hypothesised that the uplift of the Himalayas and Tibetan Plateau caused a reduction in atmospheric CO2 through increases in chemical weathering and was therefore a major causal factor in the Cenozoic Cooling trend that eventually led to our most recent series of Ice Ages.