Sensitivity of the Indian monsoon to forcing parameters and implications for its evolution

General-circulation-model simulations used to estimate the sensitivity of the Indian monsoon to changes in orbital parameters, the orography of Tibet-Himalaya, atmospheric CO2 concentration and the extent of glacial-age surface boundary conditions show that increased elevations and increased summer solar radiation are most effective in strengthening the monsoon. Strong monsoons (similar to today's) can be induced by strong solar forcing only when the elevation is at least half that of today. These conditions may have been attained in the late Miocene.